UNIVERSITY OF HELSINKIDEPARTMENT OF PLANT PRODUCTION

Section of HorticulturePUBLICATION no. 37

Pre- and postharvest development of carrotyield and quality

Terhi Suojala

Agricultural Research Centre of FinlandPlant Production Research, Horticulture

Toivonlinnantie 518FIN-21500 Piikkiö

Finland

e-mail: terhi.suojala@mtt.fi

ACADEMIC DISSERTATION

To be presented, with the permission of the Faculty of Agriculture and Forestry of theUniversity of Helsinki, for public criticism in Viikki Infocenter, Viikinkaari 11, Auditorium 2,

on 14 April, 2000, at 12 noon.

HELSINKI 2000

Supervisors: Professor Irma VoipioDepartment of Plant ProductionUniversity of Helsinki, Finland

Professor Risto TahvonenPlant Production Research, HorticultureAgricultural Research Centre of Finland

Reviewers: Professor Olavi JunttilaDepartment of BiologyUniversity of Tromsø, Norway

Professor Aarne KurppaPlant Production ResearchAgricultural Research Centre of Finland

Opponent: Professor Erkki AuraPlant Production Research, Crops and SoilAgricultural Research Centre of Finland

Cover illustration by Inge Löök (in printed version)

ISBN 951-45-9169-0 (PDF version)

Helsingin yliopiston verkkojulkaisut, Helsinki 2000

3

Contents

Preface ...................................................................................................... 4

List of original publications...................................................................... 5

Abstract..................................................................................................... 6

1 Introduction ........................................................................................... 81.1 Vegetative development and growth of carrot ................................................... 8

1.1.1 Functions and initiation of storage root....................................................... 81.1.2 Partitioning of assimilates within a plant .................................................... 91.1.3 Climatic factors affecting total plant and storage root growth .................. 10

1.2 Changes in the quality of carrot during growing season.................................. 121.2.1 Size, shape and uniformity........................................................................ 121.2.2 Carbohydrates ........................................................................................... 131.2.3 Carotenes and colour................................................................................. 131.2.4 Sensory quality.......................................................................................... 141.2.5 Compositional changes as indicators of maturity...................................... 15

1.3 Postharvest development of carrot ................................................................... 151.3.1 Factors causing storage loss...................................................................... 161.3.2 Effect of harvest time on storage loss ....................................................... 201.3.3 Effect of mechanical injuries and healing on storage loss ........................ 201.3.4 Compositional changes during storage ..................................................... 21

1.4 Aims of the study............................................................................................. 22

2 Material and methods.......................................................................... 222.1 Field experiments in 1995–1997 (I–III, V–VI)................................................ 222.2 Experiment in 1998–1999 (IV)........................................................................ 242.3 Statistical analysis ............................................................................................ 25

3 Results and discussion ......................................................................... 253.1 Patterns and cessation of carrot growth ........................................................... 253.2 Effect of harvest time on storage performance ................................................ 283.3 Changes in soluble sugar content and composition during harvest period andstorage.................................................................................................................... 323.4 Changes in sensory quality during harvest period and storage......................... 343.5 Optimisation of harvest time............................................................................ 35

4 Conclusions .......................................................................................... 36

References............................................................................................... 38

Selostus.................................................................................................... 47

4

Preface

The work described in this thesis was carried out at the Agricultural Research Centreof Finland (MTT) during 1995–1999. It has been a pleasure to work at MTT and tohave the opportunity to utilise its excellent facilities and services. The study wasstarted as a part of the research programme “Sustainable production of high-qualityvegetables”. I wish to thank those participating in the programme for the inspiringatmosphere they provided during my first steps as a scientist. My warmest thanks aredue to my closest colleague, Raili Pessala, for her help, guidance and friendly coop-eration over the years.

My work was supervised by Professor Irma Voipio and Professor Risto Ta-hvonen. I thank them both for their encouragement and insightful criticism. I amdeeply indebted to Irma Voipio for her wise questions and ideas, which helped me tomake progress in preparing the thesis. Professor Olavi Junttila and Professor AarneKurppa are gratefully acknowledged for reviewing the manuscript and for providingvaluable comments.

This work would never have been possible without much hard work by numer-ous people. I wish to express my warmest thanks to Elvi Hellstén, Johanna Huiskala,Irma Hupila, Anneli Lilja, Pirkko Vuorio, Asko Reponen, Kimmo Oravuo and thestaff at the Vegetable Experimental Site for their patient help in handling the tonnesand tonnes of carrots and for the many congenial hours we spent together. My sincerethanks are due to the carrot growers for letting me conduct the experiments on theirfields and for their positive attitude and interest in my work. Some of the farm ex-periments were organised and carried out by Saarioisten Säilyke Ltd, a contributionthat is greatly appreciated. I also thank the staff at the Häme Research Station forgiving me the opportunity to use their carrot fields and for their help.

I am most grateful to Elise Ketoja for her assistance and advice concerning thestatistical analyses. Without her ever-ready help, I would have been much more at aloss with my data. I also thank the staff at the library of MTT for their efficient andfriendly service in acquiring literature. Most of the quality analyses were performed atMTT’s Food Research. Special thanks are due to Ulla Häkkinen and the laboratoryassistants for the sugar analyses and to Tuomo Tupasela and the other carrot panelistsfor the sensory analyses. Thank you for always being willing to taste my carrots.

I express my sincere thanks to Gillian Häkli for kindly revising the English lan-guage. The cover of this thesis was illustrated by Inge Löök, to whom I owe myheartfelt thanks.

I wish to thank my colleagues and other personnel at Piikkiö for the pleasantworking atmosphere and for the many interesting and lively discussions on a wholerange of subjects. Many thanks are due to my friends for all the agreeable momentswe spent together. Finally, I should like to express my gratitude to my parents forgiving me “gardening genes” and an interest in plants. I am grateful to my father forhis continuous encouragement and confidence in me. I also thank my brother andsister for their support and friendship.

5

List of original publications

The thesis is based on the following articles, which will be referred to in the text bytheir Roman numerals.

I Suojala, T. 2000. Growth of and partitioning between shoot and storageroot of carrot in a northern climate. Agricultural and Food Science inFinland 9: 49–59.

II Suojala, T. 1999. Cessation of storage root growth of carrot in autumn.Journal of Horticultural Science & Biotechnology 74: 475–483.

III Suojala, T. 1999. Effect of harvest time on the storage performance ofcarrot. Journal of Horticultural Science & Biotechnology 74: 484–492.

IV Suojala, T. 2000. Effect of harvest time, mechanical injuries and woundhealing on infection by Mycocentrospora acerina in stored carrots(manuscript).

V Suojala, T. 2000. Variation in sugar content and composition of carrotstorage roots at harvest and during storage. Scientia Horticulturae (inpress).

VI Suojala, T. & Tupasela, T. 2000. Sensory quality of carrots: effect ofharvest and storage time. Acta Agriculturae Scandinavica, Section B,Soil and Plant Science (in press).

The articles are reprinted with the kind permission of the publishers.

6

Abstract

Suojala, T. 1 2000. Pre- and postharvest development of carrot yield and quality.University of Helsinki. Department of Plant Production. Section of Horticulture.Publication no. 37. Helsinki. 43 p. + appendices.

1Agricultural Research Centre of Finland, Plant Production Research, Horticulture,Toivonlinnantie 518, FIN-21500 Piikkiö, Finland, e-mail: terhi.suojala@mtt.fi

Storage is a prerequisite for a year-round supply of domestic vegetables. The qualityof vegetables after long-term storage is primarily determined during the growing sea-son, and storage conditions can only help to maintain the quality as long as possible.Similarly, the quantity of the marketable yield is determined by conditions during thegrowing season, and loss during storage is affected by both pre- and postharvest fac-tors.

This study aimed to show how the quality and quantity of carrot at harvest andafter storage can be better controlled. The main emphasis was on the effects of har-vest time on yield, storability and sensory quality, with the aim of optimising thetiming of harvest. In addition, development of the carrot plant during the growingseason was investigated to characterise the determinants of yield production. Thesugar composition of carrot storage root was studied as a possible descriptor of theplant’s stage of development. Field experiments were conducted at the VegetableExperimental Site of the Agricultural Research Centre of Finland and on vegetablefarms in 1995–1998. Two cultivars, ‘Fontana’ and ‘Panther’, were used, and therewere 3–6 harvests in September–October.

Despite the large variation in average yield at different growing sites, the yieldincrease generally ceased in early October. On average, 10–36% of the total yield atthe final harvest was produced after early September, when the weather was alreadyless favourable for growth. This suggests that carrot still has considerable potentialfor yield production late in the growing season. The yield increase during the harvestperiod can be estimated on the basis of thermal time.

Delaying the harvest improved storability up to late September or early October;thereafter storability remained at the same level. Only a prolonged period of frostinjured the plants so severely that their storability declined. The effect of harvest timewas similar irrespective of cultivar, growing site, year and storage conditions.Weather conditions did not account for the improved storability. It is hypothesisedthat the concentration of antifungal substances increases at the end of the growingseason, which makes the storage roots more resistant to storage pathogens. Healing at10°C for 7 days was effective in decreasing the incidence of infections caused byMycocentrospora acerina.

Changes in sugar content and composition during the harvest period were de-pendent on the year and growing site, and do not provide evidence for the existenceof any developmental stage definable as maturity. Neither do changes during storage

7

seem to be related to storage potential. A new finding in carrot was the notable dropin the sucrose and total sugar content following frost injuries on farms in 1996. Un-expectedly, this did not have an adverse effect on the storability or sensory quality ofcarrots. Sensory quality improved slightly when harvest was delayed. The two culti-vars analysed were not found to differ in sensory aspects, and the changes duringstorage were relatively small.

The results showed that the timing of harvest is an essential factor affecting theyield, quality and storability of carrot. It is concluded that, in southern Finland, theoptimal harvest time for the carrot cultivars used in the study is early October, afterwhich no major yield increase or improvement in quality or storability is to be ex-pected; a later harvest only increases the risk of frost injuries. In large areas, harvest-ing must be started early enough to get the entire crop lifted before winter. The car-rots intended for the longest storage should, however, be harvested late to minimisestorage losses. The findings concerning optimal harvest time are likely to apply toother cultivars kept in storage, too.

Key words: Daucus carota L., development, growth, harvest time, maturity, sensoryquality, storability, storage, sugars

8

1 Introduction

Carrot (Daucus carota L. ssp. sativus(Hoffm.) Schübl. & G.Martens) originatesfrom the wild forms growing in Europe andsouthwestern Asia (Banga 1984). The west-ern type of cultivated carrot is thought to de-rive from the anthocyanin-containing formsfound in Afghanistan. Cultivation of carrotspread to Europe in the fourteenth century.The first cultivated carrot types were purpleor violet; yellow and, later, orange types werederived from this anthocyanin type by selec-tion. The orange-coloured form was selectedin the Netherlands in the early seventeenthcentury.

In 1998, 18.5 million tonnes of carrotswere produced worldwide in an area of794 000 hectares (FAO 1999). On a globalscale, carrot is only a minor crop, but innorthern countries, it is one of the major fieldvegetables. In Finland in 1995–1998, theyearly production area of carrot ranged from1650 to 1954 hectares, which makes carrotthe most common field vegetable after gar-den pea (Information Centre of the Ministryof Agriculture and Forestry 1999). The har-vested yield per year varied between 52 and68 million kilograms in 1995–1998. Due tothe short growing season, most of the yieldhas to be kept in cold storage for varyinglengths of time to supply the domestic mar-ket.

Carrot has been a subject of active re-search throughout the 20th

century. Most ofthe research has arisen out of practical prob-lems, and lacks a sound theoretical back-ground. Some areas, such as biomass parti-tioning (reviews by e.g. Hole 1996, Benjaminet al. 1997), have been studied in greater de-tail. Moreover, carrot has served as a modelplant in plant physiology and more recently inbiotechnology. In Finland, carrot has beenstudied in relation to storage diseases (Mu-kula 1957), plant nutrition (Evers 1989c,Salo 1999), the effects of soil physical prop-erties (Pietola 1995) and the development of

artificial seeds (Sorvari et al. 1997).Despite the large amount of experimental

work done on carrot, problems interferingwith the production chain still exist. Thebackground of this study was the variation inthe storage performance of carrot. It is esti-mated that in Finland the average loss duringstorage can be as high as 30% (Lehtimäki1995), which represents a considerable cost.Long storage can also impair the quality ofcarrot. Preharvest factors primarily determinethe quality of the products at harvest and afterstorage; storage conditions can only help tomaintain the quality as long as possible. Byexamining the effects of developmental stageand harvest time, this study aimed to showhow the quality and quantity of carrot afterstorage could be better controlled. Develop-ment of the carrot plant during the growingseason was investigated to characterise thedeterminants of yield production. Therefore,the whole chain – from biomass partitioningin the field to maintenance of quality at theend of storage – was covered.

1.1 Vegetative development andgrowth of carrot

1.1.1 Functions and initiation of storageroot

The major ecological function of the carrotstorage root is as a reserve of assimilates forthe production of a flowering stem after ap-propriate stimuli (Hole 1996). It also formsthe route for the translocation of photosyn-thates from shoot to fibrous roots and for thetransport of water and nutrients from fibrousroots to the shoot (Benjamin et al. 1997). Itmay further act as a water reservoir, helpingto maintain a constant supply of water to theleaves (Olymbios 1973, ref. Benjamin et al.1997).

The storage organ derives mainly fromroot tissues but, in the mature state, the hypo-cotyl makes up about one inch of the upper

9

part of the storage organ (Esau 1940). Thesecondary growth resulting in the swollentaproot begins with the initiation of the sec-ondary cambium between primary xylem andprimary phloem. The cambium is formedsimultaneously with the first leaves (Esau1940). Hole et al. (1984) observed initiationof the cambium at 11 days after sowing andcompletion of the cambial ring at 20 daysafter sowing in a controlled environment.Under field conditions, initiation and com-pletion of the cambium occurred ten dayslater (Hole et al. 1987b). Esau (1940) de-scribed the development of the secondarygrowth of carrot root. Cambial cells divide toform xylem on the inside and phloem on theoutside. Most of the secondary tissues consistof parenchyma cells, which embed the ves-sels in xylem and sieve tubes and companioncells in phloem. As a consequence of en-largement of the circumference of the root,cells of the cortex and endodermis rupture. Itis at this time that the orange colour appearsin the root. Periderm, arising from meris-tematic activity in the pericycle, forms thenew protective layer. Cell division continuesthroughout the development of the storageroot in the field together with cell expansion(Hole et al. 1987c).

1.1.2 Partitioning of assimilates within aplant

Partitioning of the carbohydrates betweenplant parts is often described by the concepts“source” and “sink”. Source is a plant partthat exports more carbon than it imports,while sink is a plant part that imports morethan it exports (Ho et al. 1989). The ability ofan organ to import assimilates, sink strength,is affected by the availability of assimilatesand distance to the source and, in particular,by the genetically determined ability of thesink to compete for assimilates (Ho 1988).During vegetative growth, the storage root isconsidered as a sink, competing with fibrousroots and shoots for the assimilates produced

by photosynthetic plant parts. The relation-ship between shoot and root can be simplydescribed by estimating the ratio of theirweights. However, the ratio is often related toplant size and age (Hole 1996). The effect onplant size can be overcome by using the ratioof logarithms of organ weights, the al-lometric ratio (Richards 1969).

Hole et al. (1983) found that late matur-ing carrot cultivars have a high shoot to rootratio. Among the cultivars used in their study,high root yields tended to be associated withlarge shoots, and the highest yielding culti-vars invested in shoot growth during earlydevelopment (Hole et al. 1987a). The differ-ences between cultivars in partitioning arisevery early, a subject which has been inten-sively studied. Timing of initiation of thestorage root did not explain cultivar differ-ences in dry matter distribution (Hole et al.1987b). Hole et al. (1987a) found that theratios of the growth rates of shoot to storageroot before and after storage root initiationwere positively correlated with the shoot toroot ratio at final harvest 125 days aftersowing. Fibrous roots may also play a role inthe control of partitioning: a cultivar with alarger proportion of storage root at maturitywas found to invest more carbohydrates infibrous roots at the time of storage root ini-tiation (Hole and Dearman 1990), and varie-tal differences in allocation between storageroot and fibrous roots occurred soon afterinitiation (Hole and Dearman 1991).

Environmental conditions modify thepartitioning between shoot and storage root.Light affects the shoot to root ratios, butmostly via the effect on plant size (Hole andSutherland 1990, Hole and Dearman 1993),since the shoot to root ratio usually declineswith time and as plant weight increases (Cur-rah and Barnes 1979). Olymbios (1973, ref.Hole 1996) found an increase in shoot to rootratio at higher temperature, which may indi-cate a true change in partitioning, since thetotal weight also increased. The effect ofdensity, like that of light, is attributed to themodification of photosynthesis and growth

10

(Barnes 1979, Hole and Dearman 1993),with a lower total weight and higher shoot toroot ratio at high density or in low light.

1.1.3 Climatic factors affecting total plantand storage root growth

Storage root growth depends on the assimi-late supply from the photosynthetic plantparts. Since partitioning to the storage root ismore or less dependent on the genotype andtotal plant weight, storage root growth can beestimated from the total growth.

The main factors determining the poten-tial crop yield are leaf area, net assimilationrate, length of growing period and utilisablefraction of the biomass (harvest index)(Forbes and Watson 1992). Leaf area index(LAI, ratio of the total area of the leaves of acrop to the ground area) determines the frac-tion of interception of light. Together withthe net assimilation rate, which refers to therate of dry matter production per unit leafarea, LAI determines the rate of dry matterproduction per area at a given time. Thelength of the growing period affects the yieldby its effects on the duration of photosynthe-sis.

In addition, the growth pattern of a plantmust fit the seasonal climatic cycle. Carrothas a slow growth rate in the early part of itsvegetative development. Salo (1999) reportedthat the dry weight of the shoot increasedrapidly from July up to the middle of August,whereas the rapid dry weight accumulationinto storage roots did not start until the mid-dle of July. Evers (1988) found that 40–68%of the final shoot weight but only 17–26% ofthe final root fresh weight was reached at 2–2.5 months after sowing, in August.Therefore, much of the early part of thegrowing season is used for constructing thegrowing potential for the later part of theseason.

Irradiation

Irradiation is the primary factor regulatingphotosynthesis. Hole and Sutherland (1990)studied the effects of different light regimeson the growth of carrot at 20°C and obtainedhigher plant weights with a longer day andhigher photosynthetic photon flux density(PPFD). Comparison of light regimes withsimilar daily light integrals showed that along photoperiod (16 h, 300 µmol m-2s-1) wasmore effective than a short photoperiod andhigh PPFD (8 h, 600 µmol m-2s-1). The im-portance of photoperiod was also emphasisedby Rosenfeld et al. (1998c), who grewcarrrots at constant temperatures under dif-ferent light regimes during three periods oftime in a controlled climate. In October–De-cember, when day length was shortest andthe total amount of photosynthetically activeradiation (PAR) (natural + artificial light)was about one-third of that in the other twoperiods, the mean root size was 38 g. InApril–June and July–September, the averageday length and total level of PAR were thesame, but the roots were heavier in theautumn period (130 g), when day length wasdecreasing towards harvest, than in the springperiod (85 g), when day length increased.Therefore, long days and high radiation wereparticularly favourable during early growthstages.

Hole and Dearman (1993) found thatcarrot responded to decreasing PPFD in adifferent way from red beet and radish. Dif-ferent light intensities at a constant photo-period had no clear effect on shoot freshweight or leaf area in carrot, but the dryweight of shoot and the fresh and dry weightsof storage root and fibrous roots were re-duced in low light. The reduction in storageroot dry weight was much smaller in carrotthan in red beet and radish. According to theauthors, at decreasing PPFD, carrot main-tains leaf area and shoot fresh weight, and itsthus high photosynthetic capacity: storageroot growth is not therefore severely limited.They concluded that the asymptotic response

11

of carrot yield to high plant density is compa-rable to the response to low light, and there-fore light competition at high densities haslittle effect on the dry matter distribution incarrot.Temperature

Temperature affects growth mainly by con-trolling the rates of chemical reactions, andthus the usage of photosynthetic products.Knowledge of the temperature requirementsof carrot is still insufficient. Carrot is classi-fied as a cool-season crop, the minimumtemperature for growth being 5°C and theoptimum temperature 18–25°C (Krug 1997).Barnes (1936) found that the optimum tem-perature for carrot growth is 16–21°C. In thestudy of Bremer (1931), in which soil tem-peratures ranged from 12 to 28°C, the highestgrowth rate was obtained at 16°C. Rosenfeldet al. (1998b) grew carrots at constant tem-peratures of 9, 12, 15, 18 and 21°C and ob-served the highest root weight at 12 and15°C. However, light level had a moremarked effect on root weight than had tem-perature in the temperature range investi-gated (Rosenfeld et al. 1998c).

Wheeler et al. (1994) studied the effectsof temperature and CO2 enrichment on carrotgrowth in polyethylene-covered tunnels alongwhich a temperature gradient was imposed.A 1°C rise in mean soil temperature (in arange of 7.5 to 10.9°C) increased total weightby 37% and root weight by 34% at 134 daysafter sowing. At the stage of seven visibleleaves, no effects of temperature on root ortotal weight were found. Hence the effect oftemperature was caused by the advancedtiming of growth and development.

Olymbios (1973, ref. Benjamin et al.1997) found an increase in shoot weight withan increase in the temperature of shoot and/orroot environment from 15 to 25°C. Rootweight was also increased, but less so thanshoot weight and it fell when root tempera-ture was higher than shoot temperature. Onthe basis of this study and knowledge ofother species, Hole (1996) suggested that the

storage root has a lower temperature opti-mum than the shoot. The same phenomenonhad already been noted by Bremer (1931),who reported that storage root weight did notincrease when temperature rose above 20°C,whereas shoot weight was highest at thehighest temperature (24–26°C).

CO2

An increase in the concentration of carbondioxide in air generally enhances photosyn-thesis and growth. Dry matter production ofcarrot has also been reported to be enhancedby an increased CO2 concentration (Wheeleret al. 1994), especially at high temperatures(Idso and Kimball 1989). An increase in CO2

concentration promoted dry matter partition-ing to roots at an early growth stage (Wheeleret al. 1994) and raised the dry matter contentof shoot and root (Mortensen 1994). Awareof the possibly smaller effects of a higherCO2 concentration at low temperature,Mortensen (1994) studied the impact of anelevated CO2 level on the yield of eightvegetable species under field conditions inNorway. A significant increase in dry weightwas found only in lettuce, carrot and parsley.

Water

Water supply affects photosynthesis indi-rectly by inducing the stomata to close whenthere is a shortage of water. This results in adrop in the CO2 concentration in the leaf,which inhibits photosynthesis (Forbes andWatson 1992).

Carrot is not very sensitive to drought asit has a deep and dense root system. Pietola(1995) reported that the root system of a car-rot plant has a total length of 150–200 m at adepth of 0–50 cm. Soil compaction and irri-gation increased the length of fibrous roots inthe upper 30 cm of the soil profile.

Evers (1988) and Pietola (1995) foundonly slight effects of irrigation on final yield,regardless of the varying weather conditionsin the experimental years. Evers (1988) even

12

found that irrigation decreased yield in thefirst year, when a crust formed on the soilsurface due to heavy rain. Similarly,Dragland (1978) reported that a 3-week pe-riod of drought at an early stage, from the 2-true leaf stage onwards, increased the yield,but that drought in July–August or prior toharvest lowered the yield. Relying only onnatural precipitation resulted in the poorestyield. Sørensen et al. (1997) found thatdrought stress during a 3-week period at anygrowth stage reduced the total yield, thoughalways by less than 10%. Wind shelter mayincrease water use efficiency, since Taksdal(1992) reported yield increases and an im-provement in quality due to the erection ofartificial windbreaks especially in dry andsunny years.

However, larger yield losses due todrought have also been reported, particularlyin a warmer climate (Sri Agung and Blair1989, Prabhakar et al. 1991). Shortage ofwater also affects root shape, which is morepointed and conical under low moisture con-ditions (Barnes 1936, Sri Agung and Blair1989).To summarise, irradiation may be consideredthe main factor regulating carrot growth. Car-rot is, however, able to maintain its photo-synthetic capacity in low light better thansome other vegetable species, and thus it isamenable to growth at high plant density.Temperature affects mainly the rate of devel-opment. Moderate temperatures are the mostfavourable for the growth of carrot, and thestorage root seems to have a lower tempera-ture optimum than the shoot. An increase inthe CO2 concentration promotes dry matterproduction, and hence carrot is likely tobenefit from the greenhouse effect. Waterstress interferes with photosynthesis, but dueto the wide root system, irrigation has notalways proved profitable in carrot produc-tion. Consisting mostly of very fine roots, theroot system makes carrot relatively insensi-tive to nutrient availability, one of the basicrequirements of growth in addition to cli-matic factors.

The deteriorating environmental condi-tions for growth at the end of the growingseason in the north inhibit the yield produc-tion of carrot. However, little is known aboutthe vegetative development patterns of carrotcultivars in relation to the seasonal cycle in anorthern climate. The significance of the de-clining temperature, day length and irradi-ance in the latter part of the growing seasonis not clearly documented. Neither has theminimum temperature for growth and yieldproduction been reported in the literature.

1.2 Changes in the quality of carrotduring growing season

The optimal timing of harvest is influencednot only by yield quantity, but also bychanges in quality. According to Mazza(1989), the most important quality attributesfor carrot are size, shape, uniformity, colour,texture and internal aspects (sensory qualityand nutritional value, especially vitamin A).The following looks at the development ofthese quality attributes during the growingseason. In addition to the attributes men-tioned, changes in sugar content and compo-sition are discussed as possible descriptors ofmaturity.

1.2.1 Size, shape and uniformity

The size of the individual root increases withgrowing time and total plant weight and isaffected by plant density. Root size dependson the purpose for which the carrots will beused, but uniformity of size is a common de-mand. Models for estimating the mean rootsize and size distribution at different spacingswithin and between rows were developed byBenjamin and Sutherland (1992) and furthermodified by Benjamin and Reader (1998).

Root shape is primarily determined bygenotype but it changes during growth andcan be modified by environmental condi-tions. Low temperature (10–15°C) and a low

13

soil moisture content increase the root lengthrelative to width (Barnes 1936, Rosenfeld etal. 1998a). Rosenfeld (1998) found that cyl-indricity increased with growing time andwas lower in carrots grown at low tempera-tures. Similarly, root tips were more roundedafter a long growing time and at high tem-perature. Rounding of the root tips togetherwith simultaneous thickening and colouringwas defined as ripening (or maturation) ofthe fleshy root by Banga and de Bruyn(1968). Although Rosenfeld (1998) pointsout that the term maturity has little bearing oncarrot root, he found that cylindricity showedthe closest connection with chemical vari-ables and might be used, together with rootweight, as a criterion for fully developedroots.

1.2.2 Carbohydrates

Soluble sugars are the main form of storagecompounds in carrot. They account for 34–70% of the dry weight of the storage root andare stored in the vacuoles of the parenchymacells (Goris 1969a, Ricardo and Sovia 1974,Nilsson 1987a). Steingröver (1983) dividedthe development of carrot into three periods:period 1 (18–25 days after sowing at a con-stant temperature of 20°C), when no solublesugars are stored; period 2 (25–32 days aftersowing), when reducing sugars are stored;and period 3, when mainly sucrose is storedin the tap root. At 30–50 days after sowing,the concentration of sucrose starts to increasemore rapidly than does that of hexoses(fructose, glucose), resulting in a higher su-crose to hexose ratio (Steingröver 1981, Holeand McKee 1988). Therefore, sucrose is thepredominant transport and storage sugar atmaturity (Daie 1984), but its proportion isaffected by genotype and environment (Goris1969a, Phan and Hsu 1973, Ricardo and So-via 1974, Nilsson 1987a). Carrot cultivarsdiffer three-fold in their ability to accumulatesugars, and cultivars with high net assimila-tion rates have a capacity for high sugar yield

(Lester et al. 1982). The relationship betweenreducing and non-reducing sugars in a con-trolled environment also varies by cultivar(McKee et al. 1984).

The concentration of starch in carrotstorage roots is low, ranging from 1% to 10%of dry matter (Goris 1969b, Steingröver1981, Nilsson 1987a). Starch formation hasnot been extensively studied, but it has beensuggested that it may reflect the assimilationrate and contribute to the regulation of sugarstorage (Nilsson 1987a, Hole 1996).

Changes in the accumulation of reducingand non-reducing sugars have been related tothe activities of enzymes, e.g. acid and alka-line invertases and sucrose synthetase (Ri-cardo and ap Rees 1970, McKee et al. 1984),although enzyme activities have not alwaysshown a clear relationship with changes incarbohydrates (Hole and McKee 1988). Re-cently, Sturm et al. (1995) developed a de-tailed working model for the synthesis, trans-port, storage and usage of sucrose in carrot inwhich enzymes play a key role. Their modelwas supported by earlier results on the in-verse relationship between the activity of acidinvertase and sucrose accumulation (Ricardoand ap Rees 1970, Oldén and Nilsson 1992).

1.2.3 Carotenes and colour

Carotenes give carrot its characteristic orangecolour. There is a positive correlation be-tween carotene content and colour (Bradleyand Dyck 1968, Rosenfeld et al. 1997b).Skrede et al. (1997) found that a high caro-tene content results in a more reddish anddarker colour but a less intensive hue. Alfaand beta carotene account for more than 90%of all carotenoids in carrot (Simon and Wolff1987). A high growing temperature is knownto favour carotene production (Banga and deBruyn 1968, Rosenfeld 1998). Nilsson(1987b) found a strong positive correlationbetween carotene content and accumulatedday-degrees above 6°C. Carrots grown inmore southerly locations contained a higher

14

level of carotenes than did carrots fromnorthern growing sites (Balvoll et al. 1976,Skrede et al. 1997) and were a darker colourthan those produced further north (Hårdh etal. 1977, Baardseth et al. 1996, Rosenfeld etal. 1997a,b).

Carotene content increases with the ageand size of the root (Phan and Hsu 1973,Fritz and Weichmann 1979, Nilsson 1987a,b,Fleury et al. 1993, Rosenfeld 1998). Underfield conditions, the general trend is for anincrease in the carotene content during mostof the growing season to be followed by aconstant level of carotenes. In various stud-ies, the maximum content was reached at 90–130 days after sowing (Phan and Hsu 1973,Fritz and Habben 1975, 1977, Lee 1986,Nilsson 1987a). The carotene level wasclearly reduced when sowing was delayed upto July (Nilsson 1987a). In the greenhouse,carotenes continued to accumulate up to thelast harvest (Fritz and Habben 1977). In acontrolled climate (Rosenfeld 1998), themaximum carotene content had not beenreached at 100 days after sowing, when theexperiment was terminated.

1.2.4 Sensory quality

Sensory quality is an increasingly importantquality aspect. The contribution of differentcomponents to the sensory quality of rawcarrots has been studied but is still not fullyunderstood. Alabran and Mabrouk (1973)suggested that the non-volatile chemical con-stituents (sugars and amino acids) are pri-marily responsible for the taste of fresh carrotand that the contribution of volatile compo-nents is small compared with that of non-volatile compounds. Simon et al. (1980) em-phasised the importance of both sugars andvolatile terpenes in determining raw carrotflavour. Their findings implied that sweet-ness and overall preference are enhanced bysugars and diminished by volatiles, whereasharsh, turpentine-like flavours are associatedwith the presence of volatiles and a reduction

in sugars. Schaller et al. (1998) reported thatintensity of taste was positively correlatedwith essential oils and sweetness with sugarsin carrots cultivated at different levels of ni-trogen fertilisation. Howard et al. (1995)found that high sugar to terpinolene ratioswere associated with fresh carrot flavour,aroma, aftertaste and sweet taste. Heatherbelland Wrolstad (1971) noted that differences involatiles were quantitative rather than quali-tative. Habegger et al. (1996), however, em-phasised that the volatile composition andamount of each compound were also impor-tant for carrot aroma.

High sensory quality and sweetness havebeen reported to correlate with sugar content(Balvoll et al. 1976, Simon et al. 1982, How-ard et al. 1995). However, sugar content didnot predict sweet taste in the studies of Ro-senfeld et al. (1997b, 1998b). Rosenfeld et al.(1998b) found that the sweetest carrots,which were grown at low temperatures, con-tained the highest amounts of glucose andfructose and lower amounts of sucrose andtotal sugars. The discrepancy between sugarcontent and sweetness was partly explainedby the relative chemical sweetness, but otherfactors were also involved.

Results on the development of sensoryquality before harvest time are few, but someinformation on the effects of environmentalfactors is available. Rosenfeld et al. (1998b)observed that a low growing temperaturefavoured sweet taste, acidic taste, crispnessand juiciness of carrots, whereas high grow-ing temperatures resulted in bitter taste andhigh firmness of roots grown in phytotrons.Similar results were obtained in carrot varie-ties grown in the field in southern and north-ern Norway, and it was suggested that thevariation among geographical locations wasdetermined by growing temperature (Rosen-feld et al. 1997a,b). Rosenfeld et al. (1998c)found that temperature had a more markedeffect than light on sensory variables in car-rots grown in climate chambers. Differentday and night temperatures did not alter thesensory quality in comparison to a constant

15

temperature with the same mean temperature(Rosenfeld et al. 1999). In some experiments,growing season and site were more importantin explaining the variation in sensory qualitythan was the cultivar (Martens et al. 1985,Rosenfeld et al. 1997a,b). These findingsregarding the importance of environmentalfactors lead to the assumption that the timingof harvest might have a significant effect onsensory quality, as environmental conditionschange continuously during the growing sea-son.

Some information is available on thechanges in volatile components during thegrowing season. Heatherbell and Wrolstad(1971) found that the total essential oil con-tent remained relatively constant for the first20 weeks of the growing season but that theconcentrations of individual compoundschanged. At the end of the growing season,the total content of essential oils increased.Likewise, concentrations of acetaldehyde andethanol increased dramatically towards theend of the season, indicating anaerobic respi-ration. These changes may affect the flavourof carrot, but the subject was not analysed indepth in the study.

1.2.5 Compositional changes as indicatorsof maturity

According to Watada et al. (1984), physio-logical maturity, although not usually ob-served in organs like roots, foliage, stems andtubers, is the stage of development at which aplant or plant part will continue ontogeny,even if detached. They distinguish physio-logical maturity from “horticultural matur-ity”, the stage of development at which aplant or a plant part can be used for a par-ticular purpose. In carrot, maturity in thissense would require a satisfactory outer, sen-sory and nutritional quality combined with anadequate potential for storage and shelf life.

Several scientists have attempted to findindicators for maturity to optimise the harvesttime of carrot with regard to either nutritional

values, yield or storage potential. Sugar con-tent or composition has often been inter-preted as a maturity index. Goris (1969b) andPhan and Hsu (1973) defined maturity as thetime at which the concentration of solublesugars attains a constant value but the root isstill growing. Fritz and Weichmann (1979)suggested use of the sucrose to hexose ratioas the criterion of the appropriate harvestdate from the standpoint of nutritional qualitybut not of storage ability. Later, Le Dily et al.(1993) monitored compositional changes incarrot overwintering in the field and definedmaturity as the stage with the maximum su-crose to hexose ratio.

The use of sugar composition as an indi-cator of maturity has been questioned. InSweden, Nilsson (1987a) found that sucroseaccumulation continued up to the final har-vest, a finding at variance with the presenceof a real maturity stage. He concluded that“maturity” should only be considered as areduction in metabolic activity in an envi-ronment no longer favourable for growth.However, he mentioned that since the caro-tene content seemed to be influenced by theaccumulated day-degrees, the use of caroteneas an indicator variable should be furtherstudied. Rosenfeld (1998) noted that neitherthe ratio of sugars nor any other chemicalvariable indicated the presence of a definablestage of biological development that could beconsidered as maturity. He concluded that thecomputed term “cylindricity”, indicating rootshape, might be used as a criterion for fullydeveloped roots, together with root weight.

1.3 Postharvest development of carrot

The life of fruit and vegetables can be di-vided into three major physiological stagesfollowing germination: growth, maturationand senescence (Wills et al. 1998). Matura-tion usually starts before growth ceases andincludes different activities, depending on theproduct. Senescence is defined as the periodwhen catabolic (degradative) biochemical

16

processes overcome anabolic processes,leading to ageing and death of tissues. Afterharvest, the senescence gradually impairs thequality of the products and finally makesthem unusable.

Postharvest life functions cannot bestopped, but they can be slowed down bycontrolling the storage environment. Biologi-cal processes affecting the quality of vegeta-bles during storage are respiration, ethyleneproduction, compositional changes, growthand development, transpiration, physiologicalbreakdown, physical damage and pathologi-cal breakdown (Kader 1992). The relativeimportance of each factor varies largely fromone species to another.

1.3.1 Factors causing storage loss

Carrot has good physiological storability.Provided that carrots are not infected by mi-crobes causing storage diseases, they can bestored for 6–8 months without loss of qualityunder optimal storage conditions (tempera-ture 0°C and relative humidity c. 98%) (Bal-voll 1985). Carrot has low metabolic activityat low temperatures, as shown by the lowrespiration rate (Stoll and Weichmann 1987).A low storage temperature also prevents theonset of new growth. However, carrot is sen-sitive to wilting if not protected from waterloss. In commercial refrigerated stores, stor-age diseases, mainly caused by pathogenicfungi, pose the greatest risk. Ethylene in theair may impair the sensory quality by induc-ing the synthesis of phenolic compounds,which give rise to a bitter taste (Sarkar andPhan 1979, Lafuente et al. 1989, 1996).

Transpiration

Transpiration is the mass transfer of watervapour from the surface of the plant organ tothe surrounding air. The driving force is thegradient of water vapour pressure betweenthe tissue and the surrounding air, which isaffected by the relative humidity and tem-

perature of the air and the product (Ben-Yehoshua 1987). The rate of water loss ofcarrot is affected by the surface area of theroot, the water vapour pressure deficit and airvelocity (Apeland and Baugerød 1971). Thesignificance of the surface area is seen in thefact that large carrots lose less weight thansmall carrots and cylindrical carrots less thancone-shaped ones. Root tips, where the ratioof surface area to weight is high, are the mostsusceptible to water loss (Apeland andBaugerød 1971).

Water loss due to transpiration results inshrivelling, loss of bright colour and in-creased risk of post-harvest decay (van denBerg and Lentz 1973, Goodliffe and Heale1977, Den Outer 1990). An 8% weight lossis reported to make carrots unsaleable(Robinson et al. 1975). Van den Berg andLentz (1973) showed that the optimum rela-tive humidity during storage is 98% to 100%,a level that efficiently reduced postharvestdecay and moisture loss compared with stor-age at 90% to 95% RH. During storage, thin-walled cells, such as those in phellogen andoil ducts, die and form a fatty layer of deadcrushed cells, which accounts for the loss ofbright colour (Den Outer 1990). A new peri-derm is formed below to prevent furtherdesiccation, but the process is slow at lowtemperatures and cannot prevent water loss.

Shibairo et al. (1997) observed somecultivar differences in moisture loss charac-teristics during short-term storage but theywere mainly associated with the specific sur-face area of the root. Differences betweencultivars were pronounced when carrots wereharvested at a mature stage compared withthose harvested early. Preharvest water stressincreased postharvest weight loss and short-ened the shelf-life of carrots (Shibairo et al.1998a), which led the authors to recommendthat carrots should not be harvested underwater stress. They suggest that preharvestwater stress lowers the integrity of the mem-branes in the root, which enhances moistureloss during storage. Increased potassium (K)application reduced the postharvest moisture

17

loss by increasing root weight and maintain-ing tissue integrity, but the K fertilisation islikely to be of benefit only in soils with a verylow K content (Shibairo et al. 1998b).

Respiration

Storage compounds accumulating in the stor-age organ during growth and maturation areconsumed in the course of metabolic activi-tites during storage. Respiration includes theoxidative breakdown of sugars, starch andorganic acids into carbon dioxide and water,with the concurrent production of energy,heat and intermediary compounds to be usedin biochemical reactions (Wills et al. 1998).At low temperatures, the respiration rate islow, and it comprises only a minor part ofweight loss compared with transpiration(Apeland and Baugerød 1971). Apeland andHoftun (1974) found that respiration firstdecreased after harvest and later increasedwith time in store, more at 2 and 5°C than at0°C. Transfer to 5°C from a lower tempera-ture initially increased the respiration rateabove that at constant 5°C but the rate soondeclined.

The respiration intensity of carrots de-creases when they are harvested after alonger growing time (Fritz and Weichmann1979, Mempel and Geyer 1999). Accordingto Fritz and Weichmann (1979), in late ma-turing cultivars respiration increased again inthe final two harvests in October. The differ-ences between harvest dates persisted afterstorage but were smaller. Mempel and Geyer(1999) reported that the increase in respira-tion soon after harvest was larger in youngerthan in older carrots.

Mechanical loads increase the respirationrate, which may impair the quality of carrots(Mempel and Geyer 1999). Repeated dropsfrom a lower height resulted in a larger in-crease in respiration than did fewer dropsfrom a greater height. Respiration intensityalso increased with each step of packing.

Lowering the oxygen concentration or

increasing the carbon dioxide concentrationin storage air reduces the respiration rate ofcarrot (Apeland and Hoftun 1971, Robinsonet al. 1975), but the gas composition is criti-cal. Carrot is very sensitive to CO2 concen-trations of 4% or higher or to oxygen con-centrations of 8% or lower (Stoll andWeichmann 1987).

Fungal diseases

Storage diseases may cause considerablestorage losses, since roots showing even mi-nor damage must be discarded before mar-keting. Three pathogenic fungi, Mycocentro-spora acerina (Hartig) Deighton, Botrytiscinerea Pers. and Sclerotinia sclerotiorum(Lib.) de Bary, have been considered themost harmful throughout the production areaof carrot (Lewis and Garrod 1983) and theyare also the most common storage pathogensin Finland. In the investigation of Mukula(1957), the most important pathogens duringstorage were S. sclerotiorum, B. cinerea,Stemphylium radicum and Fusarium avena-ceum, with the first two fungi accounting for77% of the total decay. M. acerina spread toFinland in the 1970s (Tahvonen 1985) and,as a soil-borne pathogen, is today viewed asthe most serious storage disease of carrot. M.acerina has also been reported as one of themajor storage diseases in other Nordic coun-tries (Årsvoll 1969, Hermansen and Amund-sen 1987, Rämert 1988) and other temperateareas (Derbyshire and Crisp 1971, Le Cam etal. 1993).

Mycocentrospora acerina (Hartig) Deighton

Carrot roots attacked by Mycocentrosporaacerina are characterised by large, black andsunken lesions on their shoulders, sides andtips (Dixon 1981). In cross-section, the rottedarea is mainly black but it has a diffuse wa-ter-soaked brown margin (Snowdon 1992).The fungus is able to grow at temperatures of-3 to 27°C; the optimum temperature is 17–21°C (Gündel 1976).

18

1°C (Gündel 1976).The pathogen is soil-borne (Neergard

and Newhall 1951), and it survives for longperiods in the soil as dark thick-walledchlamydospores that germinate in the pres-ence of a host plant (Snowdon 1992). In-fected crop residues increase the pool ofchlamydospores in the soil, and passive dis-persal is possible by cultivation of the soiland by water running on the soil surface(Wall and Lewis 1980b); the role of air-dispersal from one field to another is insig-nificant (Hermansen 1992, Evenhuis et al.1997).

Germination of the spores is stimulatedby root exudates (Wall and Lewis 1980b).The main forms of the fungus on harvestedcarrots are chlamydospores and short lengthsof the mycelia that remain on senescent peti-oles and in soil particles attached to the roots(Davies et al. 1981). Although the senescentfoliage can maintain a supply of inoculum,foliar infection accounts for only a small pro-portion of the inoculum in the store (Walland Lewis 1980a). Infection is brought aboutby germination of the chlamydosporesthrough wounds (Davies and Lewis 1980,Davies et al. 1981).

M. acerina is predominantly a woundpathogen (Davies et al. 1981) as the root isusually infected via damaged lateral roots orabrasions in the periderm. An intact peridermis highly resistant to the pathogen, but theresistance diminishes gradually towards theinner tissues (Davies 1977, Davies and Lewis1981b, Davies et al. 1981). The resistance ofthe periderm involves inhibition of sporegermination and prevention of penetration(Davies and Lewis 1981b). Inhibition ofspore germination at the root surface declinesprogressively during storage, but as thespores age simultaneously, inhibition remainshigh and penetration of an intact periderm israre (Davies and Lewis 1981b). Resistance ofthe periderm is not likely to result from me-chanical obstruction alone as the periderm israrely completely intact (Davies and Lewis1981b).

At the beginning of carrot storage, infec-tions are microscopic (Davies et al. 1981).The small light brown areas of collapsedcells remain localised, and cells around thelesions accumulate suberin and lignin. Lig-nification and suberisation are, however, notregarded as being the main barriers to thespreading of the lesions (Davies et al. 1981).Garrod et al. (1982) considered that structuralbarriers directly contribute only a very smallproportion of the tissue resistance, but theymay protect the cell protoplasts until theyhave accumulated high levels of antimicro-bial substances. On the other hand, the onsetof progressive lesions may coincide with adecline in levels of antifungal compounds,which can therefore be regarded as an aspectof senescence (Davies et al. 1981).

The main antifungal compounds pro-duced by carrot roots, and which are activeagainst M. acerina, are falcarindiol (hep-tadeca-1,9-diene-4,6-diyne-3,8-diole; Garrodet al. 1978) and 6-methoxymellein (6-methoxy-8-hydroxy-3,4-dihydroisocoumarin;Davies 1977). The concentration of falcarin-diol decreases towards the inner tissues of theroot, which corresponds to the gradient in theresistance (Garrod et al. 1978). Olsson andSvensson (1996) found a negative correlationbetween the concentration of falcarindiol andthe susceptibility of a cultivar to M. acerinain 14 of 16 cultivars tested.

Garrod and Lewis (1979) showed thatfalcarindiol is present in the extracellular oildroplets found in periderm and pericyclicparenchyma in particular and, to a lesser ex-tent, in phloem parenchyma. Falcarindiol isknown to inhibit germination of the chlamy-dospores (Garrod et al. 1978) and also myce-lial growth of M. acerina (Garrod and Lewis1982). The antifungal effect is caused by dis-ruption of the membranes not specific tofungi. The extracellular location of falcarin-diol may prevent disruption of the mem-branes of the host plant (Garrod and Lewis1979).

The formation of 6-methoxymellein isenhanced by inoculation or infection by fungi

19

(Davies and Lewis 1981a). It also accumu-lates in response to other exogenous agents,such as heat-killed conidia of Botrytis cine-rea, surface freezing, ethylene or UV radia-tion (Harding and Heale 1981, Hoffman andHeale 1987, Hoffman et al. 1988, Mercier etal. 1993). The compound is also effectiveagainst B. cinerea. The potential to accumu-late 6-methoxymellein falls with time in stor-age (Goodliffe and Heale 1978).

Botrytis cinerea Pers.

The tissue colonised by Botrytis cinerea be-comes water-soaked, leathery and coveredwith grey mould and grey-brown spores(Snowdon 1992). Under cool humid condi-tions, the mould may remain white. The fun-gus survives in crop debris and in soil assclerotia. Vigorous young plants are not at-tacked, but the senescent foliage can be in-fected by air-borne spores or through contactwith soil or crop debris. Harvested rootscarry the infection in leaf debris, in soil at-tached to the roots or on the root surface. Thepathogen is usually present on stored carrots,e.g. in soil adhering to the root (van den Bergand Lentz 1968). During storage, the funguscan spread into adjacent roots by contact orover longer distances by air-borne spores(Goodliffe and Heale 1977). It is able togrow at temperatures of -0.3 to 35°C, with amaximum rate at 20°C (van den Berg andLentz 1968).

Resistance to infection declines in thecourse of storage (Goodliffe and Heale1977). The increased susceptibility has beenassociated with the decrease in the potentialto accumulate 6-methoxymellein (Goodliffeand Heale 1978). Weight loss of roots in-creases the incidence of infections: water lossof more than 5% markedly reduces the abilityof the phloem parenchyma to resist infection(Goodliffe and Heale 1977). Root tip, whichhas a high surface to weight ratio and is oftendamaged at harvest, is more easily infectedthan are other areas of the root. The ability of

the roots to resist infection varies from yearto year, due to differences in growing andstorage conditions.

Periderm is an effective barrier to infec-tion, but when carrots had lost water, a largerproportion of the surface inocula producedvisible lesions (Goodliffe and Heale 1977).Goodliffe and Heale (1977) suggested thatresistance to the pathogen might be due tothe accumulation of the 6-methoxymelleinfound in resistant lesions. Accumulation ofthis substance is triggered by various stressfactors (Hoffman et al. 1988), probably bythe action of an endogenous elicitor possiblyreleased after cell death. Hoffman et al.(1988) concluded that ethylene biosynthesisis required for resistance response to B. cine-rea and for the accumulation of 6-methoxymellein, but other ethylene-inducedcompounds may also affect the resistance.

Sclerotinia sclerotiorum (Lib.) de Bary

Sclerotinia sclerotiorum is one of the mostsuccessful and widely-spread plant patho-gens. According to information gathered byBoland and Hall (1994), 278 genera and 408species are reported as host plants of the fun-gus. Carrot tissue infected by S. sclerotiorumis soft and watery but not discoloured(Snowdon 1992). Pure white mould appearson the surface. Primary lesions usually occurin the crown region, but during storage themould may spread to adjacent roots by con-tact. The sclerotia form as irregularly shapedwhitish bodies that, after exuding drops ofliquid, dry out and turn to black resting bod-ies from 2 to 20 mm in size.

Sclerotia can persist in the soil for manyyears (Snowdon 1992). After wet weather orirrigation, the sclerotia germinate by produc-ing apothecia and ascospores. The spores areinjected into the air and foliage. Dense foli-age, which can retain water, and dying foli-age are susceptible to invasion. The primaryinfection is through leaf tissue very near to orin contact with sclerotia lying near the soilsurface (Finlayson et al. 1989a). The myce-

20

lium invading to leaf tissue is able to growdown the petiole to the upper part of the rootand so escape the mechanical barrier topenetration caused by root periderm. Symp-toms of the disease are rarely present at thetime of harvest, but roots have the incipientinfection when taken to store. In storage, thefungus does not form spores but spreads onlyby direct contact of the mycelium (Snowdon1992).

In the study of Le Cam et al. (1993), S.sclerotiorum was the most aggressive of thepathogens tested on carrot but only at tem-peratures above 5°C. Van den Berg andLentz (1968) found that the fungus growseven at 0°C and that it has a maximumgrowth rate at 20°C. Rapid cooling after har-vest is emphasised to control the spread ofthe fungus (Finlayson et al. 1989b, Pritchardet al. 1992).

1.3.2 Effect of harvest time on storage loss

Timing of harvest may affect storage lossesvia the effects of carrot age and develop-mental stage and weather conditions beforeand during harvest. Transpiration is affectedindirectly by the size and shape of carrots(Apeland and Baugerød 1971, Shibairo et al.1997) or directly by preharvest water stress(Shibairo et al. 1998a). The respiration rateof carrots during storage falls with thegrowing time (Fritz and Weichmann 1979,Mempel and Geyer 1999).

There is shortage of comprehensivestudies on the effect of harvest time on stor-age diseases. According to Mukula (1957),the longer the growing period the lower werethe amounts of Sclerotinia sclerotiorum andBotrytis cinerea. In one experiment, a slightincrease in storage losses due to these patho-gens was found again in the final harvest.The susceptibility of carrots to Stemphyliumradicinum and Fusarium rots increased withan increase in growing period.

Davies and Lewis (1980) and Villeneuveet al. (1993) observed a higher rate of Myco-

centrospora acerina in older carrots. Inyounger carrots, fewer inoculation sites be-came infected and fewer localised lesionsdeveloped into progressive infections (Daviesand Lewis 1980). The age of the root af-fected mainly the rate of development of lo-calised lesions and the development of pro-gressive infection, not the final level of in-fection. The resistance of the periderm tissuewas not affected by the age of the roots.Therefore, it was suggested that root agewould influence either susceptibility to dam-age or the wound-healing potential, and thatchanges in the periderm structure would nothave a direct effect on infection (Davies andLewis 1980). The greater potential forwound-healing in younger roots was reportedby Lewis et al. (1981), who found that thehealing potential declined after 176 days.

The significance of weather conditionsfor the post-harvest life of carrots was em-phasised by Fritz and Weichmann (1979),who found a positive correlation betweenstorage loss and rainfall and high humiditybefore harvest. They concluded that weatherconditions affect storage quality more thandoes the composition of the plant. Similarly,Villeneuve et al. (1993) suggested that highhumidity and precipitation, which increaseroot turgor, would make carrots more sus-ceptible to mechanical damage and thereby toinfection by M. acerina.

1.3.3 Effect of mechanical injuries andhealing on storage loss

Mechanical damage in harvest influencesdeterioration through weight loss and in-creased disease incidence. In addition, plantand soil debris among the roots increases thequantity of inoculum in the harvested yield(Derbyshire and Shipway 1978). Mechanicaldamage also raise the respiration rate andhence the consumption of reserve com-pounds of the roots (Mempel and Geyer1999).

Infections by all the pathogens studied

21

are enhanced by wounding (Mukula 1957,Derbyshire and Crisp 1971), and infection byM. acerina is restricted mainly to wounds(Davies et al. 1981). Therefore, higher ratesof diseases have been reported after me-chanical harvesting than after hand-lifting(Apeland 1974, Tucker 1974b). Neverthe-less, comparison between hand-lifted andmachine-harvested yields in two seasons(Geeson et al. 1988) did not show any con-sistent differences in the incidence of rottingdue to the major pathogens, Botrytis cinereaand Rhizoctonia carotae. Technical im-provements to the lifting machinery in recentdecades have probably reduced harvest dam-age, but injuries are still more likely to occurin mechanical harvesting than in manual har-vesting.

Wound healing is an important factor indetermining the storage potential of carrot.Davies and Lewis (1980) postulated that dif-ferences in the healing potential might alsobe related to the year-to-year variation instorage potential. Healing may be enhancedby prestorage treatments. Lewis et al. (1981)showed that healing of the wounds at 15 or25°C before storage diminished the infectionby M. acerina. On wounded phloem paren-chyma tissue, maximum resistance wasreached after 5 days’ healing. In xylem pa-renchyma, a less resistant tissue, a healingperiod as short as 6–12 hours significantlyreduced infections. Similarly, Le Cam et al.(1993) observed reduced infection by M.acerina when carrots were healed at 5–7°Cfor 12–36 hours before cold storage, andHoftun (1993) found a positive effect ofprestorage at 5°C for 2 or 3 weeks or at 10°Cfor 1 week.

Lewis et al. (1981) suggested that thebeneficial effect of healing might be attrib-uted to antifungal substances accumulatingon wound surfaces. After a 40 h healing pe-riod, Garrod and Lewis (1980) detected a 20-fold increase in the concentration of falcarin-diol in the surface layer of the wounded tis-sue, possibly due to breaking of the falcarin-diol-containing oil ducts on the wound sur-

face (Lewis et al. 1983). Lewis et al. (1983)concluded that the preformed inhibitor, falca-rindiol, is probably the main barrier to infec-tion during the first 16 h after wounding andhealing, and that its effect is reinforced by theinducible compound, 6-methoxymellein.

Most studies on wound healing havebeen conducted on artificial wounds, whichmay not fully correspond to the damagecaused by mechanical harvesting. However,in the Netherlands, it is recommended thatcarrots harvested under wet conditionsshould be given a prestorage treatment of 2–3weeks at 5°C or 1 week at 10°C to enhancethe healing process (Schoneveld and Versluis1996). When harvested under dry conditions,carrots can be taken to the store immediatelyand forced cooling is not necessary at thebeginning. The carrots should, however, beprotected from transpiration.

1.3.4 Compositional changes duringstorage

The quality of vegetables deteriorates gradu-ally during storage in response to endogenousfactors and environmental conditions. Proc-esses such as transpiration, respiration, acti-vation of growth and attacks by pathogenslead not only to quantitative losses but qualitylosses, which can destroy the marketability ofthe product or remain invisible. Composi-tional changes are usually studied only inmarketable carrots.

A common trend in sugar composition isfor the hexose content to increase and thesucrose content to decrease, especially duringthe first months of storage (Phan et al. 1973,Nilsson 1987b, Oldén and Nilsson 1992, LeDily et al. 1993). Most experiments recordonly minor changes in the total sugar content.Nilsson (1987b) found that compositionalchanges occurred irrespective of harvest dateand that the differences were maintainedthroughout storage. In natural developmentof carrot root in the field in France (Le Dilyet al. 1993), sucrose and total sugar contents

22

reached their maxima in December. The su-crose content started to decrease in mid-February and the fructose and glucose con-tents in March. In contrast to harvested andcold-stored carrots, there was no accumula-tion of hexoses. Therefore, the change incarrot composition in the post-harvest perioddiffers from that in the natural environment.

Carotene content is little affected duringstorage (Fritz and Weichmann 1979, Le Dilyet al. 1993). Phan et al. (1973) even foundthat the content increased slightly duringstorage, but when the roots started to formshoots and rootlets, the carotene content de-creased in xylem but not in phloem. The ni-trate content, which is not usually very highin carrots but may be noxious in children’sfood, decreases slightly during storage (Nils-son 1979, Kidmose and Henriksen 1994).

Changes in sensory quality during stor-age are not widely documented in the litera-ture. Evers (1989b) found that taste and tex-ture scores given after 4 or 6 months’ storagewere lower than after harvest. However, or-ganically cultivated carrots received highertaste scores after storage.

1.4 Aims of the study

Storage is a prerequisite for a year-roundsupply of domestic vegetables. The quality ofroot vegetables after long-term storage isprimarily determined during the growing sea-son. Quality is at its highest at harvest, afterwhich it can only be maintained at the sameor a lower level. The natural senescence ofproducts sets limits on the maximum periodof storage. Conditions prevailing during stor-age control the rate of postharvest changesand affect the maximum storage time. Simi-larly, the quantity of marketable yield is de-termined by conditions during the growingseason. The proportion of yield that is stillmarketable after storage is affected by bothpre- and postharvest factors.

This study aimed to show how the qual-ity and quantity of carrot after storage can be

better controlled. The main emphasis was onthe effects of harvest time, with the aim ofoptimising the timing of harvest. Criteria forthe optimal harvest time were defined as 1)high total yield, 2) low storage loss, 3) highquality of yield at harvest and 4) maintenanceof quality during storage. Development of thecarrot plant during the growing season wasinvestigated to characterise the determinantsof yield production. Evaluation of qualityconcentrated on sensory quality, which, to-gether with outer quality, is the most easilyperceptible quality characteristic in freshconsumption. The sugar composition of car-rot storage root was studied as a possibledescriptor of the plant’s stage of develop-ment.

More specific objectives were:1. to investigate the patterns of shoot andstorage root growth of carrot in a north-ern climate (I);2. to establish when the growth of carrotstorage root ceases in autumn and nofurther yield increase is gained (II);3. to determine the optimal harvest timeto minimise storage loss (III);4. to characterise the factors accountingfor changes in storability during the har-vest period (IV);5. to study changes in soluble sugarcontent and composition during the har-vest period and storage as chemical en-ergy reserves and possible descriptors ofmaturity (V); and6. to establish the optimal harvest timefor the best sensory quality at harvest andafter storage (VI).

2 Material and methods

2.1 Field experiments in 1995–1997(I–III, V–VI)

Field experiments were conducted at theVegetable Experimental Site of the Agricul-

23

tural Research Centre of Finland at Ko-kemäki and on vegetable farms. Two culti-vars were used: Panther F1 (Sluis and Groot,the Netherlands), a fresh-market varietycommonly used for storage in Finland, andFontana F1 (Bejo Zaden, the Netherlands), alate variety cultivated for the processing in-dustry. At Kokemäki, a split-plot experimentwith the two cultivars in whole plots andharvest time in subplots was conducted in1996 and 1997. There were six harvest datesat approximately 10-day intervals in Septem-ber and October (Table 1).

The experiments on farmers’ fields wereconducted:

1. to obtain a large volume of experi-mental data within three years;2. to provide insight into the variation inyield level and average storage loss be-tween farms; and3. to estimate the uniformity of the effectof harvest time under varying growingconditions.

The farm experiments were started in 1995,when the yield of cv. Fontana was harvestedfrom nine farms three times at 2-week inter-vals (Table 1). Most of the farms were lo-cated near Huittinen, two of them were nearPori and one was the Häme Research Stationat Pälkäne, which is here considered as afarm. In 1996, the experiments were contin-ued on six ‘Fontana’ farms in the Huittinenregion. Nine farms (five in the Forssa andfour in the Laitila region) with cv. Panther

were included in the study in 1996 and 1997,and there were four harvest dates at approxi-mately 2-week intervals in September andOctober.

Measurements and analyses

At the Vegetable Experimental Site, samplesfor growth analysis were taken at approxi-mately 10-day intervals starting at 43 and 54days after sowing in 1996 and 1997, respec-tively (I). The samples were analysed for thenumber of true leaves per plant (longer than0.5 cm), the length of the longest leaf, thefresh and dry weights of the leaves, themaximum thickness and length of the storageroot, and the fresh and dry weights of thestorage root. In addition, leaf area was meas-ured six times in 1996 and four times in1997. Specific leaf area (SLA) and meanrelative growth rate (RGR) were calculatedaccording to the formula given by Hunt(1990).

At each harvest date in all experiments,the variables measured were:

* total fresh and dry yield per area (noton farms in 1995) (II)* fresh weight of the shoot per plant (II)* contents of soluble sugars (fructose,glucose, sucrose) at harvest (V)* contents of soluble sugars after 2–3 du-rations of storage (only in 1995 and1996) (V)

Table 1. Harvest dates in experiments.

Coding Vegetable Experimental Site Farm experimentsof harvest cv. Fontana cv. Fontana cv. Panther cv. Panther

1996 1997 1995 1996 1996 1997H1 5 Sept 8 Sept 12 Sept 11 Sept 10–11 Sept 9–11 SeptH2 16 Sept 18 Sept 26 Sept 25 Sept 23–24 Sept 23–24 SeptH3 26 Sept 29 Sept 10 Oct 8 Oct 7–9 Oct 7–8 OctH4 7 Oct 9 Oct 22 Oct 21–22 Oct 21–22 OctH5 16 Oct 20 OctH6 28 Oct 30 OctGrowing time from sowing to H1 (d)

106 117 107–130 114–120 104–120 113–128

24

* storage losses (weight loss, proportionof diseased carrots, total loss) after 3storage durations (III).

In addition, the sensory quality of carrotsproduced at the Vegetable Experimental Siteand on 2–3 farms was analysed soon afterharvest and after 2 storage durations in 1996and 1997 (VI).

Soluble sugars were analysed at theLaboratory of Food Chemistry of the Agri-cultural Research Centre of Finland (V).Fructose, glucose and sucrose were assayedby gas-liquid chromatography (GLC) em-ploying the method of Li and Schuhmann(1980) with modifications of Haila et al.(1992). Total soluble sugars were calculatedas the sum of fructose, glucose and sucrose.

Sensory analyses were performed in co-operation with the unit for Food Chemistryand Technology of the Agricultural ResearchCentre of Finland (VI). The sensory panelhad 12 members, both people trained in sen-sory analysis and untrained vegetable spe-cialists. The attributes evaluated were juici-ness, crispness, sweetness, bitterness andoverall flavour. The first four attributes, to-gether with fruity taste, are regarded as themost important variables describing the innersensory quality of carrots by Fjeldsenden etal. (1981). Overall flavour was included todescribe the overall sensory quality of carrotsas a preference attribute. A 9-point scale wasused. For overall flavour, each integer on ascale from 1 to 9 was used but for other at-tributes, only integers 1, 3, 5, 7 and 9 wereused. Each point of the scale was given averbal description.

Storage experiments (III)

Yield samples were stored in woven poly-propylene bags (75 g m-2) in batches of ap-proximately 10 kg of carrots. Samples fromdifferent experimental sites were stored in thesame store, which differed each year. Storageconditions were as follows: in 1995–1996,temperature 0�0.5°C, relative humidity 80–85%; in 1996–1997, temperature 0�1°C, rela-

tive humidity 85–95%; in 1997–1998, tem-perature 0.5�0.5°C, relative humidity 90–100%. In the first two years, the coolingsystem comprised a refrigeration coilinstalled in the ceiling of the store. In the lastyear, an indirect cooling system with a heatexchanger cooled by outside air or bymechanical refrigeration, which maintainsthe humidity in the store, was used. In the lasttwo years, water vapour was added to the airto raise the air humidity. Storage losses wereanalysed three times during storage betweenJanuary and April.

2.2 Experiment in 1998–1999 (IV)

In 1998, carrots of cv. Panther were grown atthe Vegetable Experimental Site in a ran-domised complete block design with fourreplicate blocks. The yield was harvestedthree times (H1 = 16 September, H2 = 30September, H3 = 14 October). At each har-vest, the carrots were randomly divided intothe following treatments:

1. no mechanical treatment, storage at0.5°C2. mechanical treatment, storage at 0.5°C3. mechanical treatment + inoculationwith Mycocentrospora acerina, storageat 0.5°C4. no mechanical treatment, 7 days at10°C before storage at 0.5°C5. mechanical treatment, 7 days at 10°Cbefore storage at 0.5°C6. mechanical treatment + inoculationwith M. acerina, 7 days at 10°C beforestorage at 0.5°C.

The mechanical treatment was performed bya shaking apparatus developed in the Neth-erlands for assessing the susceptibility of po-tatoes to black spot (Meijers 1981). In treat-ments 3 and 6, the carrots were inoculatedduring shaking by adding 200 ml of coarsesand inoculated with M. acerina. Half of thecarrots (treatments 1–3) were taken straightto the cold store on the afternoon of the har-

25

vest date. Carrots from treatments 4–6 werekept for 7 days at 10°C to heal the wounds,after which they were taken to the cold store.The temperature during cold storage was0.5°C±0.5°C and relative humidity 90–100%.Storage losses were analysed on 1 Februaryand 7 April, 138 and 203 days after H1, re-spectively.

2.3 Statistical analysis

The results were analysed mainly by mixedmodels (Littell et al. 1996). In the farm ex-periments with cv. Panther, the growing area(Forssa or Laitila region) was a fixed factor,and each farm within the area was regardedas a “random” farm representing typical cul-tivation methods and conditions in that area,although the farms could not be randomlyselected (II–III, V). Therefore, it was as-sumed that results could be generalisedwithin the area, and separate farms were notof primary interest. In the experiments withcv. Fontana, all the farms represented thesame growing area, which can be regarded asthe most important production area of thiscultivar for the processing industry. When thesensory quality data from the farms wereanalysed, each farm’s data were treated sepa-rately, since only 2–3 farms were included(VI).

The models used are presented in greaterdetail in separate papers (I–IV, VI). The SASMIXED procedure (Littell et al. 1996) wasused to fit the mixed models by the restrictedmaximum likelihood (REML) estimationmethod. The effect of harvest time, whichwas the primary objective of the experiments,was further studied by estimating differencesin each response variable between harvestand the mean of following harvests.

3 Results and discussion

3.1 Patterns and cessation of carrotgrowth

Analysis of growth patterns (I) during thegrowing season showed that shoot fresh anddry weights and leaf area reached theirmaxima 90–130 days after sowing andstarted to decrease thereafter. On the otherhand, temperature and the daily sum of irra-diance remained relatively high up to ap-proximately 100 days after sowing, mid orlate August, after which they decreasedclearly. Therefore, most of the growing sea-son was used for building up the photosyn-thetic capacity, and much of the storage rootgrowth occurred under less favourable con-ditions: the storage root weight of cv.Fontana doubled and that of cv. Panther in-creased slightly less after late August. Earlierstudies on the shoot and root growth of carrotin Finland have given similar results: Salo(1999) reported that the dry weight of shootincreased up to mid August, whereas therapid growth of storage roots started in midJuly. Evers (1988) found that only 17–26%of the final root fresh weight was reached inthe middle of the growing season 2–2.5months after sowing. A slow growth rate inthe early part of vegetative growth thereforeinhibits efficient utilisation of the shortgrowing season.

Our findings on the relation between leafand storage root growth of carrot are inagreement with those of Fritz and Habben(1977), who found that, in the field, the shootweight of different cultivars declined beforethe maximum root weight was achieved. Inthe greenhouse (mean day temperature 15°C,night temperature 10°C), shoot weight startedto decrease at 100 days after emergence andunder field conditions at 130–170 days afteremergence. However, Nilsson (1987a) re-ported that the cessation of root growth at theend of September in Sweden coincided with

26

a fall in shoot weight, irrespective of sowingdate. Wheeler et al. (1994) and Habben(1972) found no decline in shoot weight upto the last harvest at 4–5 months after sow-ing. Differences in the senescence of leavesmay be related to genotype and the plant’snutritional status, but obviously maintenanceof the photosynthetic potential, even at theend of the growing season, would ensuremaximum root growth.

Hole et al. (1987a) reported that cultivarswith a high root yield tend to have high shootweights. The same was seen in our study atthe Vegetable Experimental Site, where cv.Fontana, having a high shoot weight and alarge leaf area, also produced a higher rootyield. Relative growth rates were similar inboth cultivars in relation to time from sow-ing, which shows that the differences hadarisen earlier. No clear differences in emer-gence rate of the cultivars were noticed.Therefore, the higher potential for yield for-mation in cv. Fontana seems to be deter-mined soon after emergence. Partitioning toleaf production at an early stage, resulting ina higher shoot to root ratio, apparently en-

sures a potential for high biomass productionand high root weight (Hole et al. 1987a).Hole et al. (1987a) concluded that the shootto root ratio characteristic of a given cultivarwas determined at 27–48 days from sowing.

Although the relative growth rates of thetwo cultivars were similar at a given time,they were lower in cv. Panther at a givenplant weight. This is probably due to the factthat cv. Panther reached the same plantweight later as cv. Fontana in the growingseason and therefore under less favourablegrowing conditions. The differences in rootweight between cultivars increased markedlyafter late August, suggesting that the smallerleaf area of cv. Panther was not sufficient tofully utilise the diminishing growth factors.Early development of the photosynthetic po-tential is thus crucial for achieving a highyield in a northern climate, where the shortgrowing season sets limits on growth.

Results concerning the development ofyield at the Vegetable Experimental Site andon farms (II) showed that the statisticallysignificant increase in total fresh yield gener-ally ceased in early October, despite the large

Table 2. Yield increase after different harvest dates (in comparison to final harvest). In farmexperiments, figures are means of all farms.

Vegetable Experimental Site, KokemäkiYield increase, t ha-1

(% of yield at final harvest)1996 1997

Harvest date Fontana Panther Fontana PantherH1 = 5–8 Sept 29.4 (36) 20.1 (29) 23.4 (22) 17.0 (18)H2 = 16–18 Sept 18.8 (23) 9.8 (14) 11.2 (11) 8.9 (10)H3 = 26–29 Sept 11.5 (14) 4.5 (6) 9.6 (9) 11.3 (12)H4 = 7–9 Oct 8.4 (10) -0.1 (0) -4.6 (-4) -0.2 (0)H5 = 16 Oct 3.4 (5) -1.1 (-2)Yield at final harvest 81.6 70.2 105.0 93.6

Farm experimentscv. Panther cv. Fontana1996 1997 1996

Harvest date Forssa Laitila Forssa Laitila HuittinenH1 = 9–12 Sept 14.3 (22) 4.8 (10) 16.5 (20) 19.9 (27) 6.4 (14)H2 = 23–26 Sept 5.4 (9) 1.8 (4) 5.1 (6) 6.3 (9) 4.4 (9)H3 = 7–10 Sept 3.2 (5) -1.1 (-2) -1.6 (-2) 0.9 (1) 2.6 (6)Yield at final harvest 64.0 46.6 81.9 74.3 47.0

27

variation in average yield level at differentexperimental sites. The only exceptions tothis timing were the farms at Laitila in 1996,where no yield increase was gained after thesecond harvest at the end of September. Theaverage yield gain after the first harvest was4.8–29.4 t ha-1, which corresponds to 10–36% of the total yield at the final harvest(Table 2). This means that up to one-third ofthe yield potential achieved was producedafter the first harvest in early September. How-ever, most of the yield increase was achievedbefore the end of September, and no statisti-cally significant yield gain occurred when theharvest was delayed beyond the first week ofOctober. Injuries due to night frosts on 21September and low precipitation probablypromoted leaf senescence and thereby re-duced the growth potential on farms in 1996.

The timing of cessation of growth coin-cided with earlier results, although there isprobably considerable variation between dif-ferent cultivars. In Germany, Fritz and Hab-ben (1977) found intervarietal differences inthe cessation of growth in both the green-house and the field. In the field, root growthstopped between the end of September andthe end of October. In southern Sweden, rootyield increased significantly up to 23 Sep-tember in the first year and up to 15 Octoberin the following year (Nilsson 1987b). Flønes(1973) reported that, in Norway, root growthwas slight after the beginning of October.Earlier data on yield development in the lateseason are not available for Finland.

Yield increase resulted from continuingphotosynthesis, as the dry matter yield usuallyincreased up to the same harvest as the freshyield. However, on farms in 1996, when se-vere night frosts injured the plant stands on21 September, no further accumulation of drymatter was observed. Therefore, the increasein fresh yield in that year was due to solelythe higher water content of storage roots. Thepossibility of dry matter being transportedfrom senescing leaves to storage root has notbeen studied.

These findings suggest that, despite low-

ering temperature and irradiation, carrot stillhas substantial potential for yield productionlate in the growing season if the plants re-main healthy and uninjured. The uniformtiming of cessation of growth at differentgrowing sites also suggests that the cultivarsin the study do not reach an endogenous limitfor yield production under conditions pre-vailing in Finland but that environmentalfactors determine the termination of growth.The same was noted by Rosenfeld (1998),who concluded that carrots can grow for longperiods at temperatures above those requiredfor vernalisation. Even after 3 months at atemperature as low as 9°C, carrots remainedunvernalised and continued their growth.

Development of yield could be related tothermal time from sowing to harvest. Espe-cially at Kokemäki, thermal time (TB of 0°C)produced regression models with a good fit(II, Figure 6). The results from Kokemäkisuggest that cv. Panther is able to produce,on average, 63 kg ha-1

(95% confidence in-terval (CI): 56, 70) of its root yield per oneday-degree above 0°C, and cv. Fontana ayield increase of 83 kg ha-1

(95% CI: 75, 91)per one day-degree above 0°C at the end ofthe growing season. Farm experiments withcv. Panther gave similar slope values foryield increase in response to thermal timeunless the carrot stands were injured by frosts(II, Table III). Hence, it is suggested that themodels describe the cultivar-specific re-sponse to temperature under conditions suit-able for growth. The higher response tothermal time in cv. Fontana may be due tothe larger foliage of the cultivar. Even thoughsenescence of the foliage started simultane-ously in both cultivars, the mean fresh weightof foliage remained much higher in cv.Fontana throughout the harvest season.

Since the low TB values proved success-ful in describing the yield response to tem-perature, carrot is able to utilise very lowtemperatures at the end of the growing sea-son, too. Low base temperatures have previ-ously been applied to early growth of carrot:Brewster and Sutherland (1993) obtained a

28

base temperature of 1.0°C for the seedlinggrowth of carrot. In the growth model ofBenjamin and Aikman (1995), a base tem-perature of 1.3°C was used for carrot andwhite cabbage. This was determined as thebase temperature for seed germination(Wagenvoort and Bierhuizen 1977), andBenjamin and Aikman (1995) assumed that italso applied to subsequent growth. All in all,the minimum temperature for growth anddevelopment in carrot appears to remain near0°C throughout the vegetative cycle.

Thermal time also explained the yearlydifferences in the average yield level: highyields were produced in 1997, a warm season(II). Analysis of growth showed that, in thatyear, plants invested more in leaf productionby growing a lower number of thicker andlonger leaves (I). The stronger partitioning toshoot was also seen in the linear equationsbetween shoot and root weights, where theintercepts were higher in 1997. This supportsthe suggestion that high temperature is morefavourable for shoot growth than for storageroot growth (Hole 1996). Leaf area was,however, not much higher in 1997, a findingin accordance with the data of Hole andDearman (1993), who showed that, at lowphotosynthetic photon flux density, carrotmaintains its leaf area and leaf fresh weight,but that the dry weight of leaves is dimin-ished. This limits storage root growth lessthan in red beet or radish. The maintenanceof leaf area is also seen in our results for1996, a year with less irradiance and lowertemperature, when leaf fresh and dry weightswere also reduced.

The large variation in yield level betweengrowing sites is a striking feature of the farmexperiments (II, Figure 4). The variation can-not be explained by a single factor but maybe related to difference in sowing times,drought sensitivity of the soil and otheredaphic factors. Although the levels of mac-ronutrients in soil at the time of the first har-vest and fertilisation practices were quitevariable, no clear shortage of nutrients wasobserved (data not shown). The uniformity in

yield development during the harvest perioddespite the variation in average yield suggeststhat the yield potential of a given cultivar in agiven field is determined during the early partof the growing season, e.g. by the productiv-ity of the soil and the cultivation techniqueused. In the latter part of the season, envi-ronmental conditions control the rate ofgrowth, largely irrespective of the yield al-ready produced.

3.2 Effect of harvest time on storageperformance

The timing of harvest influenced markedlythe total storage loss of carrot cvs Fontanaand Panther (III). The earliest harvests wereunfavourable for storability of the yield, anddelaying harvest decreased the storage loss.In farm experiments, the point of time afterwhich there was no further improvement instorability was H2 (25–26 September) in cv.Fontana in 1995 and 1996. In cv. Panther, theimprovement in storability continued up toH3 (7–8 October) in 1996 and up to H2 (23–24 September) in 1997. At the VegetableExperimental Site in 1996, storage loss ofboth cultivars did not decrease further afterH4 on 7 October. In 1997, storage loss wasmuch lower than the year before and itshowed a decreasing trend up to H5 on 21October, after which there was a sharp in-crease in diseases and total loss.

Even the unusually late harvest at the endof October did not increase storage loss, de-spite frost injuries and rainy weather duringthe last harvest in 1996. Only the yield fromthe very late harvest at Kokemäki on 30 Oc-tober 1997 suffered great losses. This dete-rioration in quality is easy to understand, asthe carrots were lifted from frozen soil andthe daily minimum temperatures had rangedbetween -1.0 and -12.6°C during the previ-ous 10 days.

The results from different locations showthat, under northern conditions, delaying theharvest improves storability up to the end of

29

September or beginning of October. Afterthis point in time, storability remains at aconstant level. Only a prolonged period ofvery cold weather injures the plants so se-verely that their storability is impaired.

Similar effects of harvest time have beenfound by Weichmann and Käppel (1977),who noticed that late harvesting decreasedweight loss and respiration intensity duringstorage. Only carrots from the latest harvestat the end of October had a higher weightloss and respiration intensity. Later, Fritz andWeichmann (1979) studied a larger volumeof data and found no clear relation betweenharvest time and storage loss in late maturingcultivars. The occurrence of storage diseaseswas low, and losses consisted mainly ofweight loss, which first decreased and thenincreased at the latest harvest dates. In thedata of Nilsson (1987b), the incidence ofstorage diseases fluctuated and no relation toharvest date was found.

In the present study, the effect of harvesttime was mainly due to the lower occurrenceof storage diseases in the later harvests andthe average level of diseases was higher thanin earlier studies. This may have helped re-veal the importance of harvest time. Thelargest differences between harvest dateswere observed in the yield in which diseaseinfections were common. Nevertheless, de-spite the differences in the level of diseasedcarrots in farm experiments, losses almostinvariably diminished with a later harvest(III, Figure 3).

The large between-farm variation in av-erage storage loss (III, Figure 3) cannot besatisfactorily explained. High rates of Myco-centrospora acerina were related to the fre-quent cultivation of carrot on the experimen-tal fields (Suojala and Tahvonen 1999). Thevariation in the incidence of Botrytis cinereamay be partly associated with the variation inthe mean size of the root: a negative correla-tion (r = -0.73, P = 0.042) was found be-tween mean root size and B. cinerea infec-tion on farms with cv. Panther in 1996, whenthe fungus was the major pathogen. The nu-

trient content of storage roots at differentgrowing sites did not reveal any clear rela-tionships with storage losses (data notshown). To improve the control of storability,more effort should be put into determiningstorage potential during the growing season,since the present results demonstrate that it ispossible to produce carrots with very highstorage potential.

The infection rates of both of the majorstorage pathogens, M. acerina and B. cine-rea, decreased with a later harvest. Mukula(1957) found that the amount of Sclerotiniasclerotiorum and B. cinerea decreased with alonger growing period, a finding supportedby the present results. However, the findingson M. acerina are in direct contrast to theresults of Davies and Lewis (1980) and Vil-leneuve et al. (1993), who reported a higherlevel of M. acerina in older carrots. In thestudy of Davies and Lewis (1980), theyoungest roots (127 days at harvest) were themost consistently resistant. The contradictionmight be partly explained by the age of thecarrots. Here, the age of carrots at harvestvaried between 104 and 170 days in the dif-ferent experiments and harvests and thus theplants were, on average, younger than thosestudied earlier.

Weight loss did not show any consistenttrends in relation to harvest time, but it in-creased during storage. The direct effect oftranspiration on total storage loss is usuallyvery low compared with that of storage dis-eases, provided that water loss does not leadto wilting. Indirectly, weight loss increasesstorage loss by intensifying the susceptibilityto pathogens, such as B. cinerea (Goodliffeand Heale 1977), and it may also impair theouter and sensory quality. Storage conditions(e.g. temperature, relative humidity, air cir-culation, method of cooling) affect weightloss markedly. In 1997–1998, when a storeequipped with a heat-exchanger system wasused, weight loss was much lower than in theprevious years, which may have contributedto the low total loss in that year. On the otherhand, the high incidence of B. cinerea in the

30

1996 yield may have partly resulted from therather high weight loss during storage.

The general improvement in storabilityduring the autumn was not explained byweather conditions, since the changes in pre-cipitation and air temperature were very dif-ferent in each year, whereas the changes instorability were uniform. This is in contrast tothe observations of Fritz and Weichmann(1979), who emphasised the significance ofweather conditions for the post-harvest life ofcarrots. Villeneuve et al. (1993) postulatedthat high humidity and precipitation, whichincrease root turgor, might make carrotsmore susceptible to mechanical damage andso to infection by M. acerina. This effect wasnot found in our experiments where carrotswere harvested under conditions of varyinghumidity. The significance of environmentalfactors for storability cannot, however, beexcluded. The decline in temperature of thesoil and carrot roots during the autumn has-tens the cooling of carrots when transferredto storage and so may enhance storability.Environmental conditions in late autumn mayalso be less favourable for the survival andspreading of pathogens. On the other hand, alow temperature during mechanical harvest-ing may increase the risk of harvest damageand hence provide a penetration route for thefungi to the root. All the material in the pres-ent study was hand harvested, which proba-bly resulted in a slightly lower storage lossthan in normal mechanical harvesting.

The results for 1996 and for the last har-vest in 1997 showed that carrot roots canwithstand very low temperatures without im-pairment of their storage quality. Althoughtemperatures were not measured on experi-mental fields or in the soil, recordings madenearby at ground level suggest that the tem-perature of the upper part of the root musthave fallen to -5 to -10°C. In carrots fromfarms in 1996, frost injuries were even seenas transversal cracks in the upper parts of theroots. These cracks must have been causedby ice formation in extracellular spaces, sincethe injuries did not result in disruption of the

root tissues. Tucker (1974a) studied thefreezing injuries of carrot roots by exposingoverwintered carrots to -2.5°C for 24 hours.After thawing, these roots rotted quickly.Zhang and Willison (1992) observed that,following freezing at a cooling rate of 4.8°Ch-1, carrot root samples survived temperaturesof -3 and -6°C but were partly injured at -9°C. LT50, the temperature at which half ofthe cells were killed, was as low as -12°C.The duration of the freezing stress and differ-ent stage of cold acclimation may explain thedifferences in the observed frost tolerance ofcarrot. Our observations from the field alsodemonstrate that quite a low temperature forone night is not detrimental to the storabilityof the root but that a prolonged period ofrepeated frosts, as observed between H5 andH6 at Kokemäki in 1997, does impair thestorability. A long period of frost probablyleads to some intracellular freezing and celldeath, which provides the route for thepathogens to the root.

Comparison of storage results for thedifferent years is hindered by the use of dif-ferent stores. The storage temperature wasnear optimum each year, but the variation inrelative humidity may have affected the re-sults. The polypropylene bags used in storagemitigated the effect of air humidity, but stillthe level of weight loss varied between yearsand stores. Nevertheless, preharvest condi-tions have an effect on overall storability andon the incidence of various pathogens. Pre-harvest water stress is reported to increasepostharvest weight loss (Shibairo et al.1998a), which in turn increases the suscepti-bility to B. cinerea (Goodliffe and Heale1977). Hence the low precipitation at the endof the 1996 season may partly account for thehigh occurrence of B. cinerea.

On the other hand, it has been suggestedthat high humidity and precipitation mightmake carrots more susceptible to infection byM. acerina (Villeneuve et al. 1993). Simi-larly, the infection of leaves by S. scle-rotiorum, which did not cause substantiallosses in the present study, is enhanced by

31

high humidity in the canopy (Finlayson et al.1989a, Snowdon 1992). However, changesin experimental fields and stores betweenyears do not allow in-depth analysis of thecauses for year-to year variation in averageloss; more important, the harvest time effectwas constant, irrespective of growing site,year and storage conditions.

The uniform results on the improvementin storability towards the late autumnprompted interest in the mechanisms of areduced level of infections, especially by M.acerina. Davies and Lewis (1980) suggestedthat root age influenced infections by M.acerina by affecting the susceptibility todamage or wound healing potential. McGarry(1995) showed that the tissue toughness ofcarrot storage roots increases towards the endof crop growth, making roots less susceptibleto mechanical damage and hence to storagepathogens. The contribution of mechanicaldamage and wound healing to the decrease inthe incidence of infections was studied in1998–1999 (IV).

The most important finding was that arti-ficial inoculation with M. acerina resulted infewer infections in later harvests, implyingthat the resistance of storage roots improvedin the field (IV). The mechanism of the im-proved resistance was not the lower suscepti-bility to damage, since mechanical treatmentalone did not affect the disease rate. This mayhave been caused by the low level of naturalinfection. Moreover, the method of causingmechanical damage by shaking may not havebeen effective enough. Neither could thebetter resistance to M. acerina in later har-vested carrots be attributed to the betterwound healing potential, since the relativeeffect of healing was greatest in early har-vested carrots, that is, in those with the high-est level of infections. Healing at 10°C waseffective in reducing the rate of infection byM. acerina in inoculated carrots, although theeffect was not clearly seen at the first date ofanalysis.

Combined with earlier research (Davieset al. 1981, Garrod et al. 1982), the results

led to the hypothesis that the concentration ofantifungal substances increases towards theend of the growing season, which makes thecarrots more resistant to M. acerina and pos-sibly to other storage diseases, too. The earlyharvested carrots would thus have a lowerlevel of antifungal substances, and the heal-ing period would raise their concentration,bringing it close to the level of later har-vested carrots, in which better resistancecannot be achieved. There seems to be acommon limit for resistance, probably irre-spective of the type of tissue: Lewis et al.(1981) reported that healing tended to bringinfections down to a similar level in all tis-sues despite the initial gradient in suscepti-bility. This hypothesis concerning the contri-bution of antifungal compounds needs to beassessed in future studies.

Our results suggest that infections due toM. acerina can be minimised by late har-vesting, possibly combined with a prestoragehealing treatment. Healing is especially bene-ficial for early harvested yield, which haspoor resistance to storage fungi. Preharvesthealing at 5 or 10°C, as recommended in theNetherlands for carrots harvested under wetconditions (Schoneveld and Versluis 1996),may, however, increase the risk of other dis-eases such as those caused by S. scle-rotiorum, which benefit from a higher tem-perature. In practice, temperature controlduring transport and the early phase of stor-age is dependent on many factors, such as airand soil temperature, mass of harvested yieldper day, method of storage and cooling ca-pacity. Therefore, temperature does not usu-ally drop to the recommended level very fast,which may promote healing of the woundsbut, on the other hand, may enhance thespread of S. sclerotiorum. Methods for fore-casting the quantity and species of storagediseases in the harvested yield, which havebeen tested by Hoftun (1985) and Hermansenand Amundsen (1995), would aid in opti-mising the handling of products.

As quite a short period of wound healinghas proved useful in curbing M. acerina, an

32

optimal procedure for improving the resis-tance of carrot to storage fungi could be de-veloped, possibly by combining temperaturecontrol with other methods of inducing re-sistance. The possible adverse effects ofchemical resistance agents on sensory qualityshould be kept in mind, as it is known thatsome of them, especially 6-methoxymellein(Sarkar and Phan 1979, Lafuente et al. 1989,1996) and possibly polyacetylenes (Lund1992), may import off-flavours to carrot.Proper crop rotation remains the foundationof the prevention of severe storage diseases.

3.3 Changes in soluble sugar contentand composition during harvestperiod and storage

Changes in sugar content and compositionduring the harvest period were dependent onthe year and location (V). On farms in 1995and 1997 and at the Vegetable ExperimentalSite in 1996 and 1997, the trend in sugarcomposition followed the general patternsreported in earlier studies (Goris 1969a, Phanand Hsu 1973, Ricardo and Sovia 1974,Nilsson 1987a), with an increase in the su-crose content and sucrose to hexose ratio.Fructose and glucose concentrations changedlittle during the harvest period, and anytrends found were towards lower values. Infarm experiments, the statistically significantaccumulation of sucrose continued up to H2in 1995 and up to H3 in 1997. At Kokemäki,sucrose concentrations increased statisticallysignificantly up to H4 in 1996 and up to H5in 1997.

In 1996, however, when severe frostsinjured the plants on farms on 21 September,the accumulated storage carbohydrates wereprobably used in the production of newleaves a few weeks later. Sucrose and totalsugar contents declined dramatically in bothcultivars after H2. Changes in the fructoseand glucose concentrations were small. Bydestroying part of the foliage, frost causedthe storage root to become a “source” of as-

similates. A similar effect has been noted indefoliated tap roots in which sucrose storedin vacuoles is used in the formation of newleaves (Sturm et al. 1995). Frost-injured car-rots from H6 at Kokemäki in 1997 did notstart new growth and showed no decline insugar content.

The range of total sugar content in dif-ferent harvests and years, 4.5–7.5% of freshweight, was similar to the values obtained inearlier studies conducted at northern latitudes(Balvoll et al. 1976, Evers 1989a, Hogstad etal. 1997) and at more southerly locations(Lester et al. 1982, Le Dily et al. 1993).However, higher total sugar contents andsucrose to hexose ratios have been measuredat high temperatures in a controlled climate(Rosenfeld 1998b,c) and under field condi-tions, especially after a long growing period(Weichmann and Käppel 1977, Fritz andWeichmann 1979, Le Dily et al. 1993). In thelight of of the present results and other stud-ies conducted in northern Europe (Balvoll etal. 1976, Evers 1989a, Hogstad et al. 1997),it seems likely that the relatively short andcool growing season reduces the accumula-tion of sucrose under northern conditions.

Of interest is that in farm experiments,the total sugar content and the sucrose tohexose ratio were, on average, lower in thewarm growing seasons, 1995 and 1997, thanin the cooler year, 1996, when comparing theresults for the first harvest. A high sugarcontent has previously been associated withlower temperatures (Evers 1989a, Rosenfeldet al. 1998a). Other studies, however, reporthigh sugar concentrations at higher tempera-tures (Nilsson 1987b, Hogstad et al. 1997,Rosenfeld et al. 1998b), and temperature wasfound to have a stronger influence on chemi-cal composition than light (Rosenfeld et al.1998c). These results seem to be in directcontrast to the findings of this study, at leastin terms of temperature. Note, however, thatAugust 1996 was quite warm and dry, al-though most of the growing season in thatyear was cool. The high sugar content inearly harvests in 1996 may be partly ex-

33

plained by the low precipitation in Augustand September, as drought has been reportedto increase the sucrose content of carrot(Barnes 1936, Dragland 1978).

As well as between years, the sugarcontent varied between farms. Differences inthe total sugar content at H1 could be morethan 2% units. The variation between farmswas not related to the thermal time fromsowing to harvest. The large variation in totalsugar content and composition may be due tomany environmental factors, such as micro-climate, soil type (Habben 1972), suscepti-bility of the soil to drought and differences infertilisation and other cultivation practices(Hogstad et al. 1997).

Differences between cultivars were lessdistinct than differences between growingsites and years. At the Vegetable Experi-mental Site, cv. Fontana, which is regardedas a late cultivar in Finland, had a lower su-crose to hexose ratio than had cv. Panther,the earlier cultivar. Moreover, the changesduring harvest period were slightly differentin the two cultivars. In the farm experiments,however, the sugar composition varied morebetween 1995 and 1996 in cv. Fontana thanbetween the two cultivars in 1996.

During storage, the compositionalchanges usually followed the common trend,with an increasing hexose content and a de-creasing sucrose content (Phan et al. 1973,Nilsson 1987b, Oldén and Nilsson 1992, LeDily et al. 1993). In the 1995 yield, however,the sucrose content increased once again atthe end of storage. Likewise in 1996, com-pletely opposite results were obtained for thecarrots from the last two harvests in farmexperiments. In cv. Panther in particular, thefructose and glucose concentrations de-creased and sucrose concentrations increasedduring storage.

The unusual trends observed in the lateharvests in 1996 are probably due to prehar-vest frosts which reduced the sucrose contentat harvest. The total sugar content of the in-jured carrots changed very little during stor-age, and hence most of the sucrose accumu-

lation during storage was due to the recom-bination of hexoses to sucrose. Accumulationof sucrose might be related to the ageing ofcarrot roots, which was promoted by the frostinjuries. Rutherford (1981) mentions thatsome recombination of reducing sugars tosucrose occurred after prolonged periods ofstorage, which was also observed in the 1995yield at the end of storage. Similarly, Svan-berg et al. (1997) noticed that in early culti-vars, which were more mature at the time ofharvest, sucrose increased in relation to hex-oses during storage.

The significance of the post-harvestchanges in sugar composition remains un-known. Nilsson (1987b) suggested that theaccumulation of hexoses during storage wasrelated to vernalisation and that removal offoliage and lateral roots at harvest mightstimulate the onset of hexose accumulation.This assumption was not supported by ourresults, in which the hexose accumulationoccurred after different times in storage, if atall. Compositional changes might indicatethe storage quality by affecting the behaviourof carrots after they have been taken fromstorage, an issue that has not been exten-sively studied. Changes during storage do notappear to contribute to the storage potential,since the total amount of sugars, that is thesource of energy for maintaining the metabo-lism of the plant, does not decrease muchduring cold storage and storage losses usuallyincrease linearly with time (III).

Despite the large variation in sugar com-position observed in the experimental data,changes during the harvest period do notprovide evidence for the existence of eitherphysiological or horticultural maturity, asalready noted by Rosenfeld (1998). As theroots were still growing, when the contentsof total sugar and sucrose decreased in 1996,the results do not show a clear relation be-tween root growth and sucrose accumulation.Even under “normal” growing conditions,neither the changes in the sucrose or totalsugar content nor those in the sucrose to hex-ose ratio coincided with the cessation of

34

growth (V, Table 3). Similarly, compositionalchanges do not seem to be related to stor-ability, as each year the later was the harvestthe better was the storability, with the excep-tion of the very late harvest, H6, at Kokemäkiin 1997 (III). Therefore, the compositionalchanges cannot be used to predict the storageroot growth or storage perfomance of theyield.

3.4 Changes in sensory quality duringharvest period and storage

The sensory quality of carrot was slightlyaffected when harvest was delayed (VI). AtKokemäki, the effect of harvest time wasstatistically significant in all sensory attrib-utes in 1996 and in sweetness in 1997 whichreceived higher scores for intensity in thelater harvests. Similarly, the preference at-tribute overall flavour achieved higher scoresin later harvests. No differences were foundin the sensory quality of the two cultivars,and the harvest time effect was not dependenton cultivar in either of the years. On farms,the effect of harvest time was not so clear: in1996, changes in sensory quality were statis-tically significant only on one of the threefarms, where juiciness was higher in the laterharvests. On the same farm in 1997, scoresfor all attributes except bitterness increasedafter H1 and H2. On the other farm, no cleareffects of harvest time were found in thatyear either.

The attributes most affected were juici-ness, crispness and sweetness. Harvest timeinfluenced bitterness only at Kokemäki in1996. The scores for the preference attributeoverall flavour increased with increasingjuiciness, crispness and sweetness and withdecreasing bitterness. Therefore, the carrotsfrom the later harvests seemed to have ahigher sensory quality.

The changes in sensory quality continuedup to different time points in 1996 and 1997.The risk of obtaining low sensory scores wasparticularly marked when the harvest was too

early, as were H1 and H2 at Kokemäki andH1 on farm 2. On the two other farms, noclear effect of harvest time was found. Thedependence of the harvest time effect on lo-cation may be partly related to the age of thecarrots, since the growing time from sowingto harvest was shorter on farm 2 and at Ko-kemäki than on the other farms. Therefore,the more advanced developmental stage ofcarrots from farms 1 and 3 in 1996 and fromfarm 3 in 1997 might explain the similarity inthe sensory quality of carrots harvested ondifferent dates.

Of interest is that the sensory scoresgiven for carrots from the latest harvests wereat least as high as those given for earlier har-vested carrots. Thus even the severe froststhat caused visible frost injuries to carrots onfarms in September 1996 and at Kokemäki inlate October 1997 (II) did not affect thequality. Neither did the notable decline intotal sugar content, which was on average5.9% of fresh weight in H1, 6.2% in H2 and4.8% in H3 and H4 in the yield used for sen-sory analyses in 1996 (V, Fig. 4), interferewith the sensory quality. Other factors musthave exceeded the contribution of sugarcontent to carrot flavour. This finding is incontrast to many earlier studies reporting apositive correlation between sensory qualityand sugar content (Balvoll et al. 1976, Simonet al. 1982, Schaller et al. 1998). However,Rosenfeld et al. (1997b, 1998a) showed thatsugar content did not predict sweet taste. Thesweetest carrots, which were grown at lowtemperatures, contained the highest amountsof glucose and fructose and a lower amountof sucrose and total sugars (Rosenfeld et al.1998a).

Changes in the sensory quality of mar-ketable carrots during storage were relativelysmall and therefore the sensory quality re-mained high. Only the attributes related totexture showed some decline: at Kokemäki,scores given for crispness decreased duringstorage in 1996 and those for juiciness in1997. On farm 2 in 1996, crispness decreasedduring storage. Other effects of storage time

35

were not statistically significant at the 5%level. The effect of storage is, however, diffi-cult to determine, as the evaluations wereperformed at intervals of a few months andthe panelists’ usage of the evaluation scalemay have changed with time. The harvesttime effect did not usually depend on thetime of evaluation. On farm 2 in 1997, thedifferences between harvest times werefound only after storage, not in autumn. Insome cases, the ranking of harvest timeschanged during storage (bitterness on farm 1in 1996 and juiciness on farm 3 in 1997). Onthe whole, the differences found shortly afterharvest still existed at the end of storage.

The improvement in sensory quality witha later harvest may be related to low tem-peratures at the end of the growing season,since Rosenfeld et al. (1998a) observed that alow growing temperature favoured positivesensory attributes in carrots, whereas highgrowing temperatures resulted in a bitter tasteand high firmness of roots grown in phyto-trons. The variation in sensory quality be-tween geographical locations was tentativelyattributed to growing temperature (Rosenfeldet al. 1997a,b). At the end of the growingseason, day length and the daily light integraldecrease together with temperature, but Ro-senfeld et al. (1998b) found that temperaturewas more important than light in explainingthe variation in sensory variables in carrotsgrown in climate chambers.

The two cultivars used at Kokemäkiwere not found to differ in sensory aspects.This is a somewhat surprising finding, sincethe cultivars are used for different purposes,cv. Fontana for processing and cv. Panthermainly for fresh consumption. However,Martens et al. (1985) and Rosenfeld et al.(1997a,b) showed that the variation in sen-sory quality was largely related to the grow-ing season and growing site, only a smallerpart being explained by the cultivar. There-fore, if we assume that the effect of harvesttime, like that of growing site, arises from thelowering temperature, we should expect theeffect of harvest time to exceed that of culti-

var. Since only two cultivars were used in thestudy and since both were cultivated in thesame experiment only at Kokemäki, firmconclusions cannot be drawn about the fac-tors determining sensory quality.

3.5 Optimisation of harvest time

Data on the development of marketable yieldand the average storage losses at differentharvest dates show that a later harvest tendsto produce a higher marketable yield and alower storage loss. This results in a higherquantity of marketable yield per cultivatedarea after storage and reduces the averagecost of storage per marketed kg of carrots.Timing the harvest to the very end of the sea-son, which turned out also to be favourablefor yield quality and its maintenance, is there-fore recommended. Too early a harvest wasparticularly unfavourable for the quality as-pects evaluated, that is sugar content andcomposition and sensory quality. A statisti-cally significant yield increase or improve-ment in storability usually continued up tolate September or early October.

In terms of total yield, quality and stor-age performance, harvesting in early Octoberis therefore more advantageous than an ear-lier harvest in the cultivars used in the study.Delaying harvest until after mid October in-creases the risk of frost injuries, which mayinterfere with mechanical harvesting, eventhough yield storability and quality may notsuffer. Moreover, in large areas, harvestinghas to be started early enough to be sure thatthe entire yield is harvested before winter.Root size requirements may also necessitatean earlier harvest. However, the yield in-tended for the longest storage should be har-vested late to minimise storage losses. Ob-servations on some other cultivars let us as-sume that the present findings are likely to bevalid for other cultivars used for storage, too.This optimal time of harvest applies to south-ern Finland, where most of the carrot culti-vation is located.

36

4 Conclusions

The yield potential of carrot is determinedduring early stages of growth. A large leafarea and high shoot weight developing earlyenough are the basic factors determining thepotential for high root yield, especially in anorthern climate where a slow growth ratecannot be compensated for by a longergrowing period. Maintenance of high shootweight permits the better utilisation of di-minishing growth factors at the end of thegrowing season, when decreasing tempera-ture and irradiation control the cessation ofgrowth, irrespective of plant size and yieldlevel.

In the present data, 10–36%, on average,of the total yield at the final harvest was pro-duced after early September, when theweather conditions were already less favour-able for growth. The statistically significantincrease in yield generally ceased in earlyOctober. Thus carrot still has substantial po-tential for yield production late in the grow-ing season as long as plants remain healthyand uninjured. The yield increase during theharvest period can be estimated on the basisof thermal time.

Delaying the harvest improves storabilityup to the end of September or beginning ofOctober under northern conditions, whetherthe risk for storage diseases is high or not.After this point in time, storability remains atthe same level. Only a prolonged period offrost injures the plants so severely that theirstorability is impaired. The effect of harvesttime was similar irrespective of cultivar,growing site, year and storage conditions.Weather conditions did not account for theimproved storability. The better resistance toMycocentrospora acerina could be attributedneither to the lower susceptibility to damagenor to the better potential for wound healing.It is hypothesised that the concentration ofantifungal substances increases at the end ofthe growing season, which improve the re-sistance of storage roots to storage patho-gens. Healing at 10°C was effective in miti-

gating infections by M. acerina, which mayalso be due to the accumulation of antifungalsubstances.

Changes in sugar content and composi-tion were dependent on the year and growingsite; they do not provide evidence for the ex-istence of physiological or horticultural ma-turity. Neither do changes during storageseem to be related to storage potential. A newfinding, not earlier reported in carrot, was thenotable drop in the sucrose and total sugarcontent following frost injuries. Unexpect-edly, this did not have an adverse effect onthe storability or sensory quality of carrots.

Sensory quality improved slightly whenharvest was delayed. It is concluded thatavoiding too early a harvest ensures the bestsensory quality of carrot. The two cultivarsanalysed were not found to differ in sensoryaspects, and the changes during storage wererelatively small. Therefore, high sensoryquality could be maintained up to the end ofstorage.

Combining the results on the trends inyield level, quality and storability, it is con-cluded that the optimal harvest time for thecarrot cultivated in southern Finland is earlyOctober, after which no major yield increaseor improvement in quality or storability isreached. A later harvest increases the risk offrost injuries, which may interfere with me-chanical harvesting and, after long duration,may be detrimental to storability and quality.However, over large areas, harvesting has tobe started early enough to be sure that theentire yield is harvested before winter, butcarrots intended for the longest storageshould be harvested late to minimise storagelosses. The results are likely to be valid forother cultivars used for storage, too.

The objective of this study was toachieve a better control of the quality andquantity of carrot after storage. It was shownthat the timing of harvest is an essential fac-tor affecting the yield, quality and storabilityof carrot yield, both at an experimental siteand on commercial farms. Conducting a sub-stantial part of the research on farms proved

37

successful in that a large volume of experi-mental data was obtained from a variety ofexperimental conditions and in verifying theapplicability of the results. The large varia-tion between growing sites in the averagestorage quality of carrots stresses the need forfurther studies on the determination of stor-age potential during the growing season andfor the development of methods to forecaststorability and improve the resistance to stor-age diseases.

38

References

Alabran, D.M. & Mabrouk, A.F. 1973.Carrot flavour, sugars and free nitrogenouscompounds in fresh carrots. Journal of Agri-cultural and Food Chemistry 21: 205–208.Apeland, J. 1974. Storage quality of carrotsafter different methods of harvesting. ActaHorticulturae 38: 353–357.– & Baugerød, H. 1971. Factors affectingweight loss in carrots. Acta Horticulturae 20:92–97.– & Hoftun, H. 1971. Physiological effectsof oxygen on carrots in storage. Acta Hor-ticulturae 20: 108–114.– & Hoftun, H. 1974. Effects of tempera-ture-regimes on carrots during storage. ActaHorticulturae 38: 291–308.Baardseth, P., Rosenfeld, H.J., Sundt,T.W., Skrede, G., Lea, P. & Slinde, E.1996. Evaluation of carrot varieties for pro-duction of deep fried carrot chips – II. Sen-sory aspects. Food Research International 28:513–519.Balvoll, G. 1985. Lager og lagring. Land-bruksførlaget, Oslo. 112 p.–, Apeland, J. & Auranaune, J. 1976.Chemical composition and organolepticquality of carrots grown in South- and North-Norway. Forsking og forsøk i landbruket 27:327–337.Banga, O. 1984. Carrot. In: Simmonds,N.W. (ed.). Evolution of crop plants. 3th ed.Longman, London. p. 291–293– & De Bruyn, J.W. 1968. Effect of tem-perature on the balance between proteinsynthesis and carotenogenesis in the roots ofcarrot. Euphytica 17: 168–172.Barnes, A. 1979. Vegetable plant part rela-tionships. II. A quantitative hypothesis forshoot/storage root development. Annals ofBotany 43: 487–499.Barnes, W.C. 1936. Effects of some envi-ronmental factors on growth and color ofcarrots. Cornell University, Agricultural Ex-periment Station. Memoir 186. 36 p.Benjamin, L.R. & Aikman, D.P. 1995. Pre-dicting growth in stands of mixed species

from that in individual species. Annals ofBotany 76: 31–42.–, McGarry, A. & Gray, D. 1997. The rootvegetables: beet, carrot, parsnip and turnip.In: Wien, H.C. (ed.). The Physiology ofVegetable Crops. CAB International,Wallingford. p. 553–580.– & Reader, R.J. 1998. A dynamic modelfor simulating edge effects in carrot crops.Journal of Horticultural Science & Biotech-nology 73: 737–742.– & Sutherland, R.A. 1992. Control ofmean root weight in carrots (Daucus carota)by varying within- and between-row spacing.Journal of Agricultural Science 119: 59–70.Ben-Yehoshua, S. 1987. Transpiration, wa-ter stress, and gas exchange. In: Weichmann,J. (ed.). Postharvest physiology of vegetables.Dekker, New York. p. 113–170.Boland, G.J. & Hall, R. 1994. Index ofplant hosts of Sclerotinia sclerotiorum. Ca-nadian Journal of Plant Pathology 16: 93–108.Bradley, G.A. & Dyck, R.L. 1968. Carrotcolor and carotenoids as affected by varietyand growing conditions. Proceedings of theAmerican Society for Horticultural Science93: 402–407.Bremer, A.H. 1931. Temperature and plantgrowth III. Carrot. Meldinger fra Norgeslandbrugshøgskole 11: 55–100.Brewster, J.L. & Sutherland, R.A. 1993.The rapid determination in controlled envi-ronments of parameters for predicting seed-ling growth rates in natural conditions. An-nals of Applied Biology 122: 123–133.Currah, I.E. & Barnes, A. 1979. Vegetableplant part relationships. I. Effects of time andpopulation density on the shoot and storageroot weights of carrot (Daucus carota L.).Annals of Botany 43: 475–486.Daie, J. 1984. Characterization of sugartransport in storage tissue of carrot. Journalof the American Society for HorticulturalScience 109: 718–722.Davies, W.P. 1977. Infection of carrot rootsin cool storage by Centrospora acerina. An-nals of Applied Biology 85: 163–164.

39

– & Lewis, B.G. 1980. The inter-relationshipbetween the age of carrot roots at harvest andinfection by Mycocentrospora acerina instorage. Annals of Applied Biology 95: 11–17.– & Lewis, B.G. 1981a. Antifungal activityin carrot roots in relation to storage infectionby Mycocentrospora acerina (Hartig)Deighton. New Phytologist 88: 109–119.– & Lewis, B.G. 1981b. Behaviour of Myco-centrospora acerina on periderm andwounded tissues of carrot roots. Transactionsof the British Mycological Society 77: 369–374.–, Lewis, B.G. & Day, J.R. 1981. Observa-tions on infection of stored carrot roots byMycocentrospora acerina. Transactions ofthe British Mycological Society 77: 139–151.Den Outer, R.W. 1990. Discolourations ofcarrot (Daucus carota L.) during wet chillingstorage. Scientia Horticulturae 41: 201–207.Derbyshire, D.M. & Crisp, A.M. 1971.Vegetable storage diseases in East Anglia.Proceedings of 6th

British Insecticide andFungicide Conference, Brighton. p. 167–172.– & Shipway, M.R. 1978. Control of post-harvest deterioration in vegetables in the UK.Outlook on Agriculture 9: 246–252.Dixon, G.R. 1981. Vegetable crop diseases.MaxMillan Publishers, Salisbury. 404 p.Dragland, S. 1978. Nitrogen- og vassbehovhos gulrot. Forskning og forsøk i landbruket29: 139–159.Esau, K. 1940. Developmental anatomy ofthe fleshy storage organ of Daucus carota.Hilgardia 13: 175–226.Evenhuis, A., Verdam, B. & Zadoks, J.C.1997. Splash dispersal of conidia of Myco-centrospora acerina in the field. Plant Pa-thology 46: 459–469.Evers, A.-M. 1988. Effects of different fer-tilization practices on the growth, yield anddry matter content of carrot. Journal of Agri-cultural Science in Finland 60: 135–152.– 1989a. Effects of different fertilizationpractices on the glucose, fructose, sucrose,taste and texture of carrot. Journal of Agri-cultural Science in Finland 61: 113–122.

– 1989b. Effects of different fertilizationpractices on the quality of stored carrot.Journal of Agricultural Science in Finland61: 123–134.– 1989c. The role of fertilization practices inthe yield and quality of carrot (Daucus carotaL.). Journal of Agricultural Science in Fin-land 61: 323–360.FAO 1999. FAOSTAT statistics database.Available at: http://apps.fao.org/default.htm.Finlayson, J.E., Pritchard, M.K. & Rim-mer, S.R. 1989a. Infection of carrots bySclerotinia sclerotiorum. Canadian Journalof Plant Pathology 11: 242–246.–, Pritchard, M.K. & Rimmer, S.R. 1989b.Electrolyte leakage and storage decay of fivecarrot cultivars in response to infection bySclerotinia sclerotiorum. Canadian Journalof Plant Pathology 11: 313–316.Fjeldsenden, B., Martens, M. &Russwurm, H. Jr. 1981. Sensory qualitycriteria of carrots, swedes and cauliflower.Lebensmittel-Wissenschaft und -Technologie14: 237–241.Fleury, A., Roger-Estrade, J. & Tremblay,M. 1993. La teneur en carotene de la carotteen arriere saison: etude de quelques facteursde variation. Acta Horticulturae 354: 215–219.Flønes, M. 1973. Avling og kvalitet på gulrotved forskjellige høstetider. Nordisk Jord-brugsforskning 55: 301–303.Forbes, J.C. & Watson, R.D. 1992. Plantsin agriculture. University Press, Cambridge.355 p.Fritz, D. & Habben, J. 1975. Determinationof ripeness of carrot (Daucus carota L.).Acta Horticulturae 52: 231–238.– & Habben, J. 1977. Einfluß des Erntezeit-punktes auf die Qualität verschiedenerMöhrensorten. Gartenbauwissenschaft 42:185–190.– & Weichmann, J. 1979. Influence of theharvesting date of carrots on quality andquality preservation. Acta Horticulturae 93:91–100.Garrod, B. & Lewis, B.G. 1979. Locationof the antifungal compound falcarindiol in

40

carrot root tissue. Transactions of the BritishMycological Society 72: 515–517.– & Lewis, B.G. 1980. Probable role of oilducts in carrot root tissue. Transactions of theBritish Mycological Society 75: 166–169.– & Lewis, B.G. 1982. Effect of falcarindiolon hyphal growth of Mycocentrosporaacerina. Transactions of the British Myco-logical Society 78: 533–536.–, Lewis, B.G., Brittain, M.J. & Davies,W.P. 1982. Studies on the contribution oflignin and suberin to the impedance ofwounded carrot root tissue to fungal inva-sion. New Phytologist 90: 99–108.–, Lewis, B.G. & Coxon, D.T. 1978. Cis-heptadeca-1,9-diene-4,6-diyne-3,8-diol, anantifungal polyacetylene from carrot roottissue. Physiological Plant Pathology 13:241–246.Geeson, J.D., Browne, K.M. & Everson,H.P. 1988. Storage diseases of carrots in EastAnglia 1978–82, and the effects of some pre-and post-harvest factors. Annals of AppliedBiology 112: 503–514.Goodliffe, J.P. & Heale, J.B. 1977. Factorsaffecting the resistance of cold-stored carrotsto Botrytis cinerea. Annals of Applied Biol-ogy 87: 17–28.– & Heale, J.B. 1978. The role of 6-methoxymellein in the resistance and susceptibility ofcarrot root tissue to the cold-storage patho-gen Botrytis cinerea. Physiological PlantPathology 12: 27–43.Goris, A. 1969a. Les sucres de la racine decarotte cultivée (variéte Nantaise demi-longue): variations climatiques et saison-nières, répartition dans les tissus, modifica-tion au cours du stockage. Qualitas Plan-tarum et Materiae Vegetabilis 18: 283–306.– 1969b. Métabolism glucidique de la racinede carotte cultivée (variété Nantaise demi-longue) au cours du cycle végétatif de laplante. Qualitas Plantarum et MateriaeVegetabilis 18: 307–330.Gündel, L. 1976. Untersuchungen zur Bi-ologie von Mycocentrospora acerina (Har-tig) Deighton im Zusammenhang mit derAufklärung schorfartiger Erkrankungen an

Knollensellerie. Zeitschrift für Pflanzenk-rankheiten und Pflanzenschutz 83: 591–605.Habben, J. 1972. Einfluß einiger Standort-faktoren auf Ertrag und Qualität der Möhre(Daucus carota L.). Gartenbauwissenschaft37: 345–359.Habegger, R., Müller, B., Hanke, A. &Schnitzler, W.H. 1996. GeruchsgebendeInhaltsstoffe im ätherischen Öl von verschie-denen Möhrensorten. Gartenbauwissenschaft61: 225–229.Haila, K., Kumpulainen, J., Häkkinen, U.& Tahvonen, R. 1992. Sugar and organicacid contents of vegetables consumed inFinland during 1988–1989. Journal of FoodComposition Analysis 5: 100–107.Harding, V.K. & Heale, J.B. 1981. Theaccumulation of inhibitory compounds in theinduced resistance response of carrot rootslices to Botrytis cinerea. Physiological PlantPathology 18: 7–15.Heatherbell, D.A. & Wrolstad, R.E. 1971.Carrot volatiles. 2. Influence of variety, ma-turity and storage. Journal of Food Science36: 225–227.Hermansen, A. 1992. Mycocentrosporaacerina in carrots: Host range, epidemiologyand prediction. Agricultural University ofNorway. Doctor Scientarum Theses 1992:7.– & Amundsen, T. 1987. Lag-ringssjukdommer på gulrot. Aktuelt fraStatens fagtjenesten for landbruket 4: 257–267.– & Amundsen, T. 1995. Two methods forthe prediction of Mycocentrospora acerinainfection on stored carrots. Annals of Ap-plied Biology 126: 217–233.Ho, L.C. 1988. Metabolism and compart-mentation of imported sugars in sink organsin relation to sink strength. Annual Reviewof Plant Physiology and Molecular Biology39: 355–378.–, Grange, R.I. & Shaw, A.F. 1989.Source/sink regulation. In: Baker, D.A. &Milburn, J.A. Transport of photoassimilates.Longman, Harlow. p. 306–343.Hoffman, R.M. & Heale, J.B. 1987. 6-Methoxymellein accumulation and induced

41

resistance to Botrytis cinerea Pers. ex Pers.,in carrot root slices treated with phytotoxicagents and ethylene. Physiological Plant Pa-thology 30: 67–75.–, Roebroeck, E. & Heale, J.B. 1988. Ef-fects of ethylene biosynthesis in carrot rootslices on 6-methoxymellein accumulationand resistance to Botrytis cinerea. Physiolo-gia Plantarum 73: 71–76.Hoftun, H. 1985. Testing av lagringsevnehos gulrot. Meldinger fra Norges Land-brukshøgskole 64: 1–11.– 1993. Nedkjøling av gulrot. Verknad pålagringsevne og kvalitet. Norsk land-bruksforsking 7: 147–155.Hogstad, S., Risvik, E. & Steinsholt, K.1997. Sensory quality and chemical compo-sition in carrots: a multivariate study. ActaAgriculturae Scandinavica, Section B, Soiland Plant Science 47: 253–264.Hole, C.C. 1996. Carrots. In: Zamski, E. &Schaffer, A.A. (eds.). Photoassimilate distri-bution in plants and crops. Marcel Dekker,New York. p. 671–690.–, Barnes, A., Thomas, T.H., Scott, P.A. &Rankin, W.E.F. 1983. Dry matter distribu-tion between the shoot and storage root ofcarrot (Daucus carota L.). I. Comparison ofvarieties. Annals of Botany 51: 175–187.– & Dearman, J. 1990. Partition of 14C as-similate between organs and fractions ofcontrasting varieties of carrot during initia-tion of the storage root. Journal of Experi-mental Botany 41: 557–564.– & Dearman, J. 1991. Carbon economy ofcarrots during initiation of the storage root incultivars contrasting in shoot:root ratio atmaturity. Annals of Botany 68: 427–434.– & Dearman, J. 1993. The effect of photonflux density on distribution of assimilate be-tween shoot and storage root of carrot, redbeet and radish. Scientia Horticulturae 55:213–225.– & McKee, J.M.T. 1988. Changes in solu-ble carbohydrate levels and associated en-zymes of field-grown carrots. Journal ofHorticultural Science 63: 87–93.–, Morris, G.E.L. & Cowper, A.S. 1987a.

Distribution of dry matter between shoot andstorage root of field-grown carrots. I. Onsetof differences between cultivars. Journal ofHorticultural Science 62: 335–341.–, Morris, G.E.L. & Cowper, A.S. 1987b.Distribution of dry matter between shoot andstorage root of field-grown carrots. II. Rela-tionship between initiation of leaves andstorage roots in different cultivars. Journal ofHorticultural Science 62: 343–349.–, Morris, G.E.L. & Cowper, A.S. 1987c.Distribution of dry matter between shoot andstorage root of field-grown carrots. III. De-velopment of phloem and xylem parenchymaand cell numbers in the storage root. Journalof Horticultural Science 62: 351–358.– & Sutherland, R.A. 1990. The effect ofphoton flux density and duration of the pho-tosynthetic period on growth and dry matterdistribution in carrot. Annals of Botany 65:63–69.–, Thomas, T.H. & McKee, J.M.T. 1984.Sink development and dry matter distributionin storage root crops. Plant Growth Regula-tion 2: 347–358.Howard, L.R., Braswell, D., Heymann, H.,Lee, Y., Pike, L.M. & Aselage, J. 1995.Sensory attributes and instrumental analysisrelationships for strained processed carrotflavor. Journal of Food Science 60: 145–148.Hunt, R. 1990. Basic growth analysis. Un-win Hyman, London. 112 p.Hårdh, J.E., Persson, A.R. & Ottosson, L.1977. Quality of vegetables cultivated at dif-ferent latitudes in Scandinavia. Acta Agri-culturae Scandinavica 27: 81–96.Idso, S.B. & Kimball, B.A. 1989. Growthresponse of carrot and radish to atmosphericCO2 enrichment. Environmental and Ex-perimental Botany 29: 135–139.Information Centre of the Ministry of Ag-riculture and Forestry 1999. HorticulturalEntreprise Register 1998 (Puutarhayritys-rekisteri 1998). Agriculture and Forestry1999:2. 108 p.Kader, A.A. 1992. Postharvest biology andtechnology: an overview. In: Kader, A.A.Postharvest technology of horticultural crops.

42

2nd ed. University of California, Oakland,CA. p. 15–20.Kidmose, U. & Henriksen, K. 1994.Ernæringsmæssig kvalitet af gulerødder, – irelation til kvælstoftilførsel og lagring.Statens Planteavlsforsøg 2: 75–81.Krug, H. 1997. Environmental influences ondevelopment, growth and yield. In: Wien,H.C. (ed.). The Physiology of VegetableCrops. CAB International, Wallingford. p.101–180.Lafuente, M.T., Cantwell, M., Yang, S.F.& Rubatzky, V. 1989. Isocoumarin contentof carrots as influenced by ethylene concen-tration, storage temperature and stress condi-tions. Acta Horticulturae 258: 523–534.–, López-Gálvez, G., Cantwell, M. & Yang,S.F. 1996. Factors influencing ethylene-induced isocoumarin formation and increasedrespiration in carrots. Journal of the Ameri-can Society for Horticultural Science 121:537–542.Le Cam, B., Rouxel, F. & Villeneuve, F.1993. Analyse de la flore fongique de la ca-rotte conservée au froid: prépondérance deMycocentrospora acerina (Hartig) Deighton.Agronomie 13: 125–133.Le Dily, F., Villeneuve, F. & Boucaud, J.1993. Qualité et maturité de la racine de ca-rotte: influence de la conservation au champet au froid humide sur la composition bio-chimique. Acta Horticulturae 354: 187–199.Lee, C.Y. 1986. Changes in carotenoid con-tent of carrots during growth and post-harvest storage. Food Chemistry 20: 285–293.Lehtimäki, S. 1995. Puutarhatuotteidenvarastointikustannukset Suomessa. (Storagecosts of horticultural products in Finland). (InFinnish). Puutarhaliitto, Helsinki. Puu-tarhaliiton julkaisuja nro 284. (Publicationsof the Central Organization for Finnish Hor-ticulture no. 284). 62 p.Lester, G.E., Baker, L.R. & Kelly, J.F.1982. Physiology of sugar accumulation incarrot breeding lines and cultivars. Journal ofthe American Society for Horticultural Sci-ence 107: 381–387.

Lewis, B.G. , Davies, W.P. & Garrod, B.1981. Wound-healing in carrot roots in rela-tion to infection by Mycocentrosporaacerina. Annals of Applied Biology 99: 35–42.– & Garrod, B. 1983. Carrots. In: Dennis,C. (ed.). Post-harvest pathology of fruits andvegetables. Academic Press, London, p. 103–124.–, Garrod, B. & Sullivan, C. 1983. Accu-mulation of antifungal compounds on woundsurfaces of carrot root tissue. Transactions ofthe British Mycological Society 80: 183–184.Li, B. & Schuhmann, P. 1980. Gas-liquidchromatographic analysis of sugars in ready-to-eat breakfast cereals. Journal of Food Sci-ence 45: 138–141.Littell, R.C, Milliken, G.A., Stroup, W.W.& Wolfinger, R.D. 1996. SAS®

System forMixed Models. SAS Institute Inc, Cary, NC.633 p.Lund, E.D. 1992. Polyacetylenic carbonylcompounds in carrots. Phytochemistry 31:3621–3623.Martens, M., Rosenfeld, H.J. &Russwurm, H. Jr. 1985. Predicting sensoryquality of carrots from chemical, physical andagronomical variables: a multivariate study.Acta Agriculturae Scandinavica 35: 407–420.Mazza, G. 1989. Carrots. In: Eskin, N.A.(ed.). Quality and Preservation of Vegetables.CRC Press, Boca Raton. p. 75–119.McGarry, A. 1995. Cellular basis of tissuetoughness in carrot (Daucus carota L.) stor-age roots. Annals of Botany 75: 157–163.McKee, J.M.T., Thomas, T.H. & Hole,C.C. 1984. Growth regulator effects on stor-age root development in carrot. Plant GrowthRegulation 4: 203–211.Meijers, C.P. 1981. Diseases and defectsliable to affect potatoes during storage. In:Rastovski, A. et al. Storage of potatoes. Post-harvest behaviour, store design, storagepractice, handling. Centre for AgriculturalPublishing and Documentation, Wageningen.p. 138–166.Mempel, H. & Geyer, M. 1999. Einflußmechanischer Belastungen auf die Atmung-

43

saktivität von Möhren. Gartenbauwissen-schaft 64: 118–125.Mercier, J., Arul, J., Ponnampalam, R. &Boulet, M. 1993. Induction of 6-methoxymellein and resistance to storagepathogens in carrot slices by UV-C. Journalof Phytopathology 137: 44–54.Mortensen, L.M. 1994. Effects of elevatedCO2 concentrations on growth and yield ofeight vegetable species in a cool climate. Sci-entia Horticulturae 58: 177–185.Mukula, J. 1957. On the decay of storedcarrots in Finland. Acta Agriculturae Scandi-navica. Supplementum 2. 132 p.Neergard, P. & Newhall, A.G. 1951. Noteson the physiology and pathogenicity of Cen-trospora acerina (Hartig) Newhall. Phyto-pathology 41: 1021–1033.Nilsson, T. 1979. Yield, storage ability,quality and chemical composition of carrot,cabbage and leek at conventional and organicfertilizing. Acta Horticulturae 93: 209–223.– 1987a. Growth and chemical compositionof carrots as influenced by the time of sowingand harvest. Journal of Agricultural Science(Camb.) 108: 459–468.– 1987b. Carbohydrate composition duringlong-term storage of carrots as influenced bythe time of harvest. Journal of HorticulturalScience 62: 191–203.Oldén, B. & Nilsson, T. 1992. Acid and al-kaline invertase activities in carrot duringroot development and storage. Swedish Jour-nal of Agricultural Research 22: 43–47.Olsson, K. & Svensson, R. 1996. The influ-ence of polyacetylenes on the susceptibilityof carrots to storage diseases. Journal ofPhytopathology 144: 441–447.Olymbios, C.M. 1973. Physiological studieson the growth and development of carrot,Daucus carota L. PhD thesis, University ofLondon. Ref. Benjamin et al. 1997, Hole1996.Phan, C. & Hsu, H. 1973. Physical andchemical changes occurring in the carrot rootduring growth. Canadian Journal of PlantScience 53: 629–634.

–, Hsu, H. & Sarkar, S.K. 1973. Physicaland chemical changes occurring in the carrotroot during storage. Canadian Journal ofPlant Science 53: 635–641.Pietola, L. 1995. Effect of soil compactnesson the growth and quality of carrot. Agricul-tural Science in Finland 4: 139–237.Prabhakar, M., Srinivas, K. & Hegde,D.M. 1991. Efffect of irrigation regimes andnitrogen fertilization on growth, yield, N up-take, and water use of carrot (Daucus carotaL.). Gartenbauwissenschaft 56: 206–209.Pritchard, M.K., Boese, D.E. & Rimmer,S.R. 1992. Rapid cooling and field-appliedfungicides for reducing losses in stored car-rots caused by cottony soft rot. CanadianJournal of Plant Pathology 14: 177–181.Ricardo, C.P.P. & ap Rees, T. 1970. In-vertase activity during the development ofcarrot roots. Phytochemistry 9: 239–247.– & Sovia, D. 1974. Development of tuber-ous roots and sugar accumulation as relatedto invertase activity and mineral nutrition.Planta 118: 43–55.Richards, F.J. 1969. The quantitative analy-sis of plant growth. In: Stewards, F.C. et al.(eds.). Plant Physiology. V A. Analysis ofgrowth: behaviour of plants and their organs.Academic Press, New York, London. p. 3–76.Robinson, J.E., Browne, K.M. & Burton,W.G. 1975. Storage characteristics of somevegetables and soft fruits. Annals of AppliedBiology 81: 399–408.Rosenfeld, H.J. 1998. Maturity and devel-opment of the carrot root (Daucus carota L.).Gartenbauwissenschaft 63: 87–94.–, Risvik, E., Samuelsen, R.T. & Rødbot-ten, M. 1997a. Sensory profiling of carrotsfrom northern latitudes. Food Research In-ternational 30: 593–601.–, Baardseth, P. & Skrede, G. 1997b.Evaluation of carrot varieties for productionof deep fried carrot chips. IV. The influenceof growing environment on carrot raw mate-rial. Food Research International 30: 611–618.

44

–, Samuelsen, R.T. & Lea, P. 1998a. Rela-tionship between physical and chemicalcharacteristics of carrots grown at northernlatitudes. Journal of Horticultural Science &Biotechnology 73: 265–275.–, Samuelsen, R.T. & Lea, P. 1998b. Theeffect of temperature on sensory quality,chemical composition and growth of carrots(Daucus carota L.) I. Constant diurnal tem-perature. Journal of Horticultural Science &Biotechnology 73: 275–288.–, Samuelsen, R.T. & Lea, P. 1998c. Theeffect of temperature on sensory quality,chemical composition and growth of carrots(Daucus carota L.) II. Constant diurnal tem-peratures under different seasonal light re-gimes. Journal of Horticultural Science &Biotechnology 73: 578–588.–, Samuelsen, R.T. & Lea, P. 1999. Theeffect of temperature on sensory quality,chemical composition and growth of carrots(Daucus carota L.) III. Different diurnaltemperature amplitudes. Journal of Horticul-tural Science & Biotechnology 74: 196–202.Rutherford, P.P. 1981. Some biochemicalchanges in vegetables during storage. Annalsof Applied Biology 98: 538–541.Rämert, B. 1988. Lagringssjukdomar påmorötter. Sveriges Lantbruksuniversitet,Uppsala. Växtskyddsrapporter. Trädgård 5.44 p.Salo, T. 1999. Effects of band placement andnitrogen rate on dry matter accumulation,yield and nitrogen uptake of cabbage, carrotand onion. Agricultural and Food Science inFinland 8: 157–232.Sarkar, S.K. & Phan, C.T. 1979. Naturally-occurring and ethylene induced phenoliccompounds in the carrot root. Journal ofFood Protection 42: 526–534.Schaller, R.G., Broda, S. & Schnitzler,W.H. 1998. Chemische, chemosensorischeund humansensorische Untersuchungen zuGeschmack und Aroma von Möhren.Nahrung 42: 400–405.Schoneveld, J.A. & Versluis, H.P. 1996.Natmaken, drogen en helen van peen enwitlofwortels. Proefstation voor de Akker-

bouw en de Groenteteelt in de Vollegrond,Lelystad. Verslag nr. 221.Simon, P.W., Peterson, C.E. & Lindsay,R.C. 1980. Correlations between sensory andobjective parameters of carrot flavor. Journalof Agricultural and Food Chemistry 28: 559–562.–, Peterson, C.E. & Lindsay, R.C. 1982.Genotype, soil, and climate effects on sen-sory and objective components of carrot fla-vour. Journal of the American Society forHorticultural Science 107: 644–648.– Wolff, X.Y. 1987. Carotenes in typicaland dark orange carrots. Journal of Agricul-tural and Food Chemistry 35: 1017–1022.Shibairo, S.I., Upadhyaya, M.K. &Toivonen, P.M.A. 1997. Postharvest mois-ture loss characteristics of carrot (Daucuscarota L.) cultivars during short-term stor-age. Scientia Horticulturae 71: 1–12.–, Upadhyaya, M.K. & Toivonen, P.M.A.1998a. Influence of preharvest water stresson postharvest moisture loss of carrots (Dau-cus carota L.). Journal of Horticultural Sci-ence & Biotechnology 73: 347–352.–, Upadhyaya, M.K. & Toivonen, P.M.A.1998b. Potassium nutrition and postharvestmoisture loss in carrots (Daucus carota L.).Journal of Horticultural Science & Biotech-nology 73: 862–866.Skrede, G., Nilsson, A., Baardseth, P., Ro-senfeld, H.J., Enersen, G. & Slinde, E.1997. Evaluation of carrot varieties for pro-duction of deep fried carrot chips – III. Ca-rotenoids. Food Research International 30:73–81.Snowdon, A.L. 1992. Color atlas of post-harvest diseases & disorders of fruits &vegetables. Vol 2. Vegetables. Wolfe Pub-lishing, Aylesbury. 416 p.Sørensen, J.N., Jørgensen, U. & Kühn,B.F. 1997. Drought effects on the marketableand nutritional quality of carrots. Journal ofthe Science of Food and Agriculture 74:379–391.Sorvari, S., Toldi, O., Ahanen, K., Vii-namäki, T., Hakonen, T. & Tahvonen, R.1997. Using polysaccharides and galacto-

45

mannans as gelling agents in capsule forma-tion of artificial seeds. Journal of the Ameri-can Society for Horticultural Science 122:878–883.Sri Agung, I.G.A.M. & Blair, G.J. 1989.Effects of soil bulk density and water regimeon carrot yield harvested at different growthstages. Journal of Horticultural Science 64:17–25.Steingröver, E. 1981. The relationship be-tween cyanide-resistant root respiration andthe storage of sugars in the taproot in Daucuscarota L. Journal of Experimental Botany 32:911–919.– 1983. Storage of osmotically active com-pounds in the taproot of Daucus carota L.Journal of Experimental Botany 34: 425–433.Stoll, K. & Weichmann, J. 1987. Rootvegetables. In: Weichmann, J. (ed.). Posthar-vest physiology of vegetables. Dekker, NewYork. p. 541–553.Sturm, A., Sebková, V., Lorenz, K.,Hardegger, M., Lienhard, S. & Unger, C.1995. Development- and organ-specific ex-pression of the genes for sucrose synthaseand three isoenzymes of acid 8-fructofuranosidase in carrot. Planta 195:601–610.Suojala, T. & Tahvonen, R. 1999. Effect ofcrop rotation on storage diseases of carrot.In: Hägg, M. et al. (eds.). Agri-Food QualityII. Quality management of fruits and vegeta-bles. The Royal Society of Chemistry, Cam-bridge. p. 76–77.Svanberg, S.J.M., Nyman, E.M.G., An-dersson, R., Nilsson, T. 1997. Effects ofboiling and storage on dietary fibre and di-gestible carbohydrates in various cultivars ofcarrot. Journal of the Science of Food andAgriculture 73: 245–154.Tahvonen, R. 1985. The prevention of Bo-trytis cinerea and Sclerotinia sclerotiorum oncarrots during storage by spraying the topswith fungicide before harvesting. AnnalesAgriculturae Fenniae 24: 89–95.

Taksdal, G. 1992. Windbreak effects on thecarrot crop. Acta Agriculturae Scandinavica.Section B. 42: 177–183.Tucker, W.G. 1974a. Freezing injury in car-rots. Journal of Horticultural Science 49: 29–35.– 1974b. The effect of mechanical harvestingon carrot quality and storage performance.Acta Horticulturae 38: 359–374.van den Berg, L. & Lentz, C.P. 1968. Theeffect of relative humidity and temperatureon survival and growth of Botrytis cinereaand Sclerotinia sclerotiorum. Canadian Jour-nal of Botany 46: 1477–1481.– & Lentz, C.P. 1973. High humidity stor-age of carrots, parsnips, rutabagas and cab-bage. Journal of the American Society forHorticultural Science 98: 129–132.Villeneuve, F., Bosc, J-P. & Luneau, C.1993. La conservation en chambre froide:étude de quelques facteurs. Acta Horticultu-rae 354: 221–232.Wagenvoort, W.A. & Bierhuizen, J.F.1977. Some aspects of seed germination invegetables. II. The effect of temperaturefluctuation, depth of sowing, seed size andcultivar, on heat sum and minimum tem-perature for germination. Scientia Horticultu-rae 6: 259–270.Wall, C.J. & Lewis, B.G. 1980a. Infectionof carrot leaves by Mycocentrosporaacerina. Transactions of the British Myco-logical Society 75: 163–164.– & Lewis, B.G. 1980b. Survival of chlamy-dospores and subsequent development of Mycocentrospora acerina in soil. Transac-tions of the British Mycological Society 75:207–211.Watada, A.E., Herner, R.C., Kader, A.A.,Romani, R.J. & Staby, G.L. 1984. Termi-nology for the description of developmentalstages of horticultural crops. HortScience 19:20–21.Weichmann, J. & Käppel, R. 1977. Har-vesting dates and storage-ability of carrots(Daucus carota L.). Acta Horticulturae 62:191–196.Wheeler, T.R., Morison, J.I.L., Ellis, R.H.

46

& Hadley, P. 1994. The effects of CO2, tem-perature and their interaction on the growthand yield of carrot (Daucus carota L.). Plant,Cell and Environment 17: 1275–1284.Wills, R., McGlasson, B., Graham, D. &Joyce, D. 1998. Postharvest. An introductionto the physiology & handling of fruit, vegeta-bles & ornamentals. 4th

ed. CAB Interna-tional, Wallingford. 262 p.

Zhang, M.I.N. & Willison, J.H.M. 1992.Electrical impedance analysis in plant tissues:The effect of freeze-thaw injury on the elec-trical properties of potato tuber and carrotroot tissues. Canadian Journal of Plant Sci-ence 72: 545–553.Årsvoll, K. 1969. Pathogens on carrots inNorway. Meldinger fra Norges Land-brukshøgskole 48 (2). 55 p.

47

Selostus

Porkkanasadon määrän ja laadun muuttuminen kasvukaudella ja varastoinninaikana

Kotimaisten vihannesten ympärivuotinen tarjonta edellyttää varastointia. Vihannesten laatu va-rastoinnin jälkeen määräytyy suurelta osin jo kasvukauden aikana, ja varasto-oloilla voidaan vainpyrkiä säilyttämään laatu mahdollisimman pitkään. Kasvukauden aikaiset tekijät ratkaisevatmyös sadon määrän. Varastoinnin aikaiseen määrälliseen hävikkiin vaikuttavat sekä kasvukau-den että varastoinnin aikaiset tekijät.

Tämän tutkimuksen tavoitteena oli parantaa porkkanan varastoinnin jälkeistä laatua ja pie-nentää varastohävikkiä. Tutkimuskohteena oli erityisesti sadonkorjuun ajoittumisen vaikutussadon määrään, varastokestävyyteen ja aistittavaan laatuun, tavoitteena korjuuajan optimointi.Lisäksi tutkittiin kasvin kehitystä kasvukaudella ja kasvumuuttujien yhteyttä sadontuottoon.Porkkanan varastojuuren sokerikoostumusta tutkittiin mahdollisena kehitysvaiheen kuvaajana.Kenttäkokeet tehtiin MTT:n vihanneskoepaikalla Kokemäellä ja vihannestiloilla vuosina 1995–1998. Kokeissa käytettiin lajikkeita ‘Fontana’ ja ‘Panther’, ja satoa korjattiin 3–6 kertaa syys–lo-kakuussa

Sadon määrä kasvoi yleensä lokakuun alkupuolelle asti huolimatta keskisadon suurestavaihtelusta koepaikkojen välillä. Keskimäärin 10–36 % viimeiseen korjuukertaan mennessä tuo-tetusta sadosta syntyi syyskuun alun jälkeen, jolloin sääolot olivat jo vähemmän otolliset kasvul-le. Tämä osoittaa, että porkkanalla on huomattava sadontuottokyky vielä kasvukauden lopulla.Sadonlisäys korjuukaudella voidaan arvioida lämpösumman perusteella.

Sadonkorjuun siirtäminen syyskuun loppuun tai lokakuun alkuun paransi varastokestävuuttä.Tätä myöhäisempikään korjuu ei heikentänyt säilyvyyttä. Vasta pitkään jatkunut pakkasjaksovaurioitti porkkanoita niin, että niiden säilyvyys heikkeni. Sadonkorjuuajan vaikutus oli saman-lainen lajikkeesta, kasvupaikasta, vuodesta ja varasto-oloista riippumatta. Sääolot eivät selittä-neet säilyvyyden muutoksia. Varastotautien kestävyyden lisääntymisen arvellaan johtuvan anti-fungaalisten aineiden kertymisestä porkkanan juureen. Sadonkorjuuta seurannut viikon mittainenesijäähdytys 10 °C:n lämpötilassa vähensi porkkananmustamädän aiheuttamia varastotappioitaverrattuna suoraan kylmävarastointiin.

Varastojuuren sokeripitoisuuden ja -koostumuksen muutokset sadonkorjuukaudella vaihteli-vat vuosien ja kasvupaikkojen välillä, joten ne eivät näytä soveltuvan kehitysvaiheen kuvaajaksi.Myöskään varastoinnin aikaiset muutokset sokereiden määrissä tai suhteissa eivät näytä liittyvänvarastokestävyyteen. Porkkanoiden aistittava laatu parani hieman, kun sadonkorjuuta siirrettiinmyöhempään. Kahden tutkitun lajikkeen välillä ei havaittu eroja aistittavassa laadussa. Aistittavalaatu ei myöskään muuttunut selvästi varastoinnin aikana.

Tulosten mukaan sadonkorjuun ajoittuminen vaikuttaa oleellisesti porkkanasadon määrään,laatuun ja varastokestävyyteen. Tutkittujen lajikkeiden optimaalinen korjuuaika Etelä-Suomessaon lokakuun alkupuoli, jonka jälkeen ei ole odotettavissa merkittävää sadonlisäystä tai varasto-kestävyyden ja aistittavan laadun paranemista. Myöhäinen korjuu lisää pakkasvaurioiden riskiä.Suurilla viljelyaloilla sadonkorjuu on aloitettava ajoissa ennen talven tuloa, mutta pitkään varas-toitavat erät olisi syytä korjata myöhään varastotappioiden minimoimiseksi. Korjuuajan vaikutuslienee samanlainen myös muilla varastointiin soveltuvilla lajikkeilla.

Avainsanat: aistittava laatu, Daucus carota L., kasvu, kehitys, sadonkorjuuaika, sokerit, varas-tointi, varastokestävyys