spikelet initiation of winter triticale and winter wheat in response to nitrogen fertilization

European Journal of Agronomy 11 (1999) 107–113

Spikelet initiation of winter triticale and winter wheat inresponse to nitrogen fertilization

F. Ewert a,*, B. Honermeier ba Department of Agricultural Sciences, The Royal Veterinary & Agricultural University, Agrovej 10, DK-2630 Taastrup, Denmark

b Institute of Agronomy and Plant Breeding, Justus Liebig University, Ludwigstraße 23, D-35390 Gießen, Germany

Accepted 12 February 1999

Abstract

Spikelet initiation in response to two levels of nitrogen fertilization (0 and 200 kg N ha−1 split into5×40 kg N ha−1) was investigated on the main stem and the first initiated tiller of winter triticale (TriticosecaleWITTM., cv. Grado) and winter wheat (Triticum aestivum L., cv. Taras) grown at Rostock, Germany (54.2°N) infour seasons (1987–1991). Plants were sampled every 3–10 days between plant emergence and anthesis, and thenumber of spikelet primordia, the lengths of the shoot apex and shoot were recorded. Nitrogen effects on spikeletnumber per ear were analyzed at the end of the rapid rate of spikelet initiation (EorSI) and at anthesis.

The duration of spikelet initiation was not affected by nitrogen application in both cereals. The numbers ofspikelets of both main stems and tillers were significantly increased due to nitrogen fertilization at EorSI and anthesis(2.3 and 2.6 spikelets per ear, respectively) in wheat. Nitrogen fertilization did not affect spikelet number per ear atEorSI in triticale but significantly increased spikelet number on main stems and tillers at anthesis (2.4 spikelets perear), which was explained by the continuation of spikelet initiation after EorSI in the high-nitrogen treatment andspikelet abortion in the treatment without nitrogen application. Spikelet abortion was observed in both nitrogentreatments in wheat. Main stems initiated more spikelets per ear than tillers. However, spikelet initiation on mainstems and tillers did not respond differently to nitrogen application for triticale or wheat. Variation of spikeletinitiation among years was affected by nitrogen application. In wheat, spikelet number per ear varied less amongyears when nitrogen was applied. In triticale, the variation in spikelet number increased with nitrogen application.There was a positive relationship between the duration of spikelet initiation and the nitrogen effect on spikelet numberper ear at EorSI for triticale. In both cereals, nitrogen application increased both the length of the shoot and thelength of the shoot apex, which, however, did not result in a relationship between the effects of nitrogen applicationon spikelet number and either shoot length or apex length. Spikelet initiation in response to nitrogen fertilization oftriticale and wheat is discussed with respect to differences in the developmental performance and the morphologicalcharacteristics of the apical differentiation between the two cereals. It is concluded that spikelet initiation in triticalewas better adapted to low nitrogen conditions than wheat. Our results suggest that consideration of nitrogen supplyis important when analysing the variation in spikelet inititation and relationships between growth and differentiationprocesses. © 1999 Elsevier Science B.V. All rights reserved.

Keywords: Main stem; Nitrogen fertilization; Spikelet initiation; Tiller; Triticale; Wheat

Corresponding author. Tel. : +45-3528-3377; fax: +45-3528-2175.E-mail address: [email protected] (F. Ewert)

1161-0301/99/$ – see front matter © 1999 Elsevier Science B.V. All rights reserved.PII: S1161-0301 ( 99 ) 00023-4

108 F. Ewert, B. Honermeier / European Journal of Agronomy 11 (1999) 107–113

1. Introduction

Spikelet number per ear is an important elementdetermining grain number and grain yield in cere-als. Nitrogen fertilization has often been shown toincrease the number of spikelets per ear in wheat(e.g. Langer and Liew, 1973; Whingwiri and Kemp,1980; Frank and Bauer, 1982; Darwinkel, 1983)basically, due to an increase in the rate of spikeletinitiation (Whingwiri and Kemp, 1980).

Triticale has become an interesting alternativeto wheat or barley as a feed grain at sites withunfavourable growing conditions or in low-inputsystems ( Karpenstein-Machan et al., 1994).However, information about spikelet initiation intriticale in response to nitrogen fertilization is rare.Nitrogen effects on spikelet initiation of tillers ascompared to main stems were investigated in wheat( Whingwiri and Kemp, 1980; Darwinkel, 1983).No such investigations are known for triticale.Few studies have analysed spikelet initiation intriticale in comparison with wheat (Hunt andChapleau, 1986; Ewert, 1996) and rye (Hunt and

Fig. 1. Summary of rainfall totals and average temperatures atChapleau, 1986). However, comparative studiesRostock, 1987–1991.between triticale and other cereals that have con-

sidered the effects of nitrogen fertilization on spike- split-plot design with the two cereals as main plotslet initiation are scarce. and nitrogen treatment with four replicates as

The present study analyses spikelet initiation subplots. Seeds were sown between 1 and 4on main stems and the first tiller of two cultivars October, depending on the year, by machine to aof winter triticale (cv. Grado) and winter wheat depth of 3–5 cm with 12.5 cm between rows at(cv. Taras) grown in the field with and without a density of 500 seeds m−2. Emergence variednitrogen application during four experimental sea- between 80 and 98% of seeds sown. We assumedsons (1987–1991). Since there is still a need to that spikelet initiation was not affected by theunderstand the relationships between sink develop- variation in plant emergence since additionalment and growth processes, particularly in cases experiments have shown that spikelet initiation didof nitrogen deficiency (Abbate et al., 1995), we not respond to a variation in plant density betweenalso analysed the effects of nitrogen fertilization 250 and 750 plants m−2 (Ewert, 1994). Crop man-on spikelet initiation in relation to apex and agement was consistent with local agronomic prac-shoot growth. tices (i.e. crop protection from pests and diseases

and weed control ). The plant growth regulatorCCC (chlormequat) was applied (3 l ha−1) at the2. Materials and methodsbeginning of stem elongation. Lodging did notoccur before anthesis. The weather conditions mea-2.1. Experimental detailssured from sowing to anthesis are summarised inFig. 1. A limitation of water on plant growth wasWinter triticale (cv. Grado) and winter wheatobserved in May/June 1989, just prior to anthesis.(cv. Taras) were grown in field experiments atSpikelet initiation was investigated for plantsRostock, Germany (54.2°N), a site with an annualgrown in two nitrogen treatments: 0 kg N ha−1rainfall of 600 mm, on a sandy loam soil between

1987 and 1991. Plots were arranged in form of a and 200 kg N ha−1. Nitrogen was applied as

109F. Ewert, B. Honermeier / European Journal of Agronomy 11 (1999) 107–113

calcium ammonium nitrate in 5×40 kg N ha−1amounts at the onset of spring growth and atgrowth stages 22–24, 30/31, 33/34 and 51 (Zadokset al., 1974) to give a non-limiting supply ofnitrogen throughout the growing season. Soilsamples were taken in early spring to analyse theamount of mineral nitrogen (NO3 and NH4) avail-able in two soil layers. Mineral nitrogen in the soilwas between 12 and 26 kg N ha−1 and between 10and 20 kg N ha−1 for the soil layers from 0 to30 cm and from 30 to 60 cm, respectively, depend-ing on the year.

Fig. 2. General form of the three-stage linear model that wasapplied to determine rate, duration and end of the rapid rate2.2. Measurements and data analysisof spikelet primordia initiation. S, sowing; BorSI, beginning ofthe rapid rate of spikelet initiation; EorSI, end of the rapid rateSpikelet initiation was studied on eight plantsof spikelet initiation; An, anthesis. Spikelet initiation continued

sampled every 3–10 days, a frequency that at a low rate after EorSI only in triticale in the high nitrogendepended on the rate of development after seedling treatment (see text).emergence. The number of leaf and spikelet pri-mordia, the length and the developmental stage of duration of spikelet initiation. In the presentthe shoot apex, and the length of the shoot were experiment, there was no effect of nitrogen fertil-recorded on the main shoot and the first tiller. ization on the duration of spikelet initiation forSpikelet primordia were counted when they could the main stem and the first tiller in either of thebe identified under a microscope. Spikelets that cereals (data not shown). Thus, nitrogen effects onhad developed at least one floret were considered

spikelet number at EorSI were due to the effectsin the spikelet counts at anthesis. Information onof nitrogen fertilization on the rate of spikeletdevelopmental stages of main stems and tillers isinitiation.given in Ewert et al. (1996). A three-stage linear

Analyses of variance of the effects of year,model (Ewert, 1996) was used to determine thecereal, tiller group and nitrogen fertilization onbeginning, end (EorSI) and rate and duration ofthe number of spikelets per ear were performed atrapid spikelet initiation (Fig. 2). This approachEorSI and at anthesis (Table 1). Generally, spike-was found to be useful in comparing spikeletlet number per ear varied significantly among yearsinitiation between the two cereals, since the present(Table 1) and was significantly higher in triticalecultivar of triticale did not form ‘terminal spike-than in wheat at both dates (Tables 1 and 2).lets’, which morphologically determine the end ofFurther, spikelet number was higher on main stemsspikelet initiation in wheat. The spikelet numberthan on the first tillers and was significantlyper ear was analysed in detail at EorSI and atincreased by nitrogen fertilization at EorSI and atanthesis. Appropriate analyses of variance wereanthesis (Tables 1 and 2). However, there wereperformed with SPSS PC. All factors were classi-interactions between year and cereal at EorSI andfied as ‘fixed’. Treatment means were comparedanthesis and between cereal and tiller group atusing Student’s t-tests.anthesis (Table 1), which have already been ana-lysed by Ewert (1996). Interestingly, the ANOVAresults also identify a cereal×nitrogen interaction3. Resultsat EorSI and a year×cereal×nitrogen interactionat anthesis (Table 1). The number of spikelets on3.1. Nitrogen effects on spikelet numbermain stems and tillers was affected little by nitro-gen fertilization at EorSI in triticale (Table 2).Spikelet number at the end of rapid spikelet

initiation (EorSI ) is determined by the rate and However at anthesis, nitrogen fertilization signifi-


Table 1 cantly increased spikelet number on main stemsAnalyses of variance of the number of spikelets per ear at the and tillers in triticale by an average of 2.4 spikeletsend of the rapid rate of spikelet initiation (EorSI ) and anthesis

per ear (Table 2). In wheat, spikelet numbers onof the main stem and the first tiller of winter triticale and wintermain stems and tillers were significantly increasedwheat grown in two nitrogen treatments and in 4 yearsaas a result of nitrogen application at both EorSI

Source of variation DF MSQb (2.3 spikelets per ear) and anthesis (2.6 spikeletsper ear) (Table 2). Interestingly, spikelet initiationEorSI Anthesiswas observed to continue after EorSI in triticale

Main effects 6 1056.4*** 1034.6*** when nitrogen was applied (Table 2). In the highYear (Y ) 3 301.5*** 66.8*** nitrogen treatment, the spikelet number was higherCereal (C) 1 5323.7*** 4956.0*** (1.1 spikelet per ear) at anthesis than at EorSI.Tiller group (TG) 1 55.1*** 52.1**

No such increase in spikelet number was observedNitrogen fertilization (N) 1 143.5*** 170.2***in the low nitrogen treatment (Table 2). In wheat,Two-way interaction 12 17.7*** 31.2***

Y×C 3 43.7*** 97.3*** the number of spikelets per ear was at a maximumY×TG 3 6.2 11.9 at EorSI. Spikelet abortion was observed afterY×N 3 3.3 18.5* EorSI in both nitrogen treatments (Table 2).C×TG 1 9.7 20.9*C×N 1 37.5*** 0.2TG×N 1 1.5 0.8 3.2. Variation of spikelet initiation in response toThree-way interaction 10 3.2 5.8 nitrogen fertilizationY×C×TG 3 3.7 2.5Y×C×N 3 5.9 15.5*

Variation among years in the number of spike-Y×TG×N 3 1.0 2.1lets per ear was observed to depend on the rate ofC×TG×N 1 0.2 1.4

Four-way interaction nitrogen application (Fig. 3). Nitrogen fertiliza-Y×C×TG×N 3 1.7 4.5 tion caused a small increase in the variation ofExplained 31 212.5*** 239.3*** spikelet number per ear in triticale. In contrast toResidual 165 3.2 5.2

this, nitrogen application in wheat was associatedTotal 196 36.3 42.3with a considerable decrease in the yearly variation

a DF, degrees of freedom; MSQ, mean squares. of spikelet number on both dates, EorSI andb *, **, *** Significant at p=0.05, 0.01 and 0.001, respectively. anthesis (Fig. 3). It is also worth mentioning that,

at anthesis, the variation in spikelet number waslower than that observed at EorSI for both nitro-

Table 2Spikelet number per ear of the main stem (MS) and the first tiller (T1) of winter triticale (cv. Grado) and winter wheat (cv. Taras)in response to nitrogen fertilization at the end of the rapid rate of spikelet initiation (EorSI) and anthesis

Developmental stage Treatment Triticalea Wheata

MS T1 Mean MS T1 Mean

EorSI N0 30.1 28.9 29.5 18.4 18.3 18.3N200 31.1 29.3 30.2 21.1 20.3 20.7N200–N0 1.0 0.4 0.7 2.7*** 2.0** 2.3***

Anthesis N0 30.1 27.7 28.9 17.9 16.3 17.1N200 32.5 30.2 31.3 19.8 19.5 19.6N200–N0 2.4** 2.5* 2.4** 1.9** 3.2** 2.6***

Spikelet abortion (Anthesis-EorSI ) N0 −0.1 −1.3 −0.6 −0.5 −2.0 −1.3N200 1.4 0.9 1.1 −1.3 −0.8 −1.0

a *, **, *** Significant at p=0.05, 0.01 and 0.001, respectively.


Fig. 4. Relationship between the effect of nitrogen fertilizationFig. 3. Coefficient of variation (CV ) of spikelet number per ear on spikelet number per ear (N200/N0) and the duration of thefor two levels of nitrogen fertilization (0 and 200 kg N ha−1) at rapid rate of spikelet initiation (rSI, Tb=0°C ) for main stemsthe end of the rapid rate of spikelet initiation (EorSI ) and ($) and tillers (6) of winter triticale (cv. Grado). Data areanthesis of winter triticale (cv. Grado) and winter wheat (cv. from 3 years of experimentation, 1988–1991. ** Significant atTaras, 1987–1991). Since responses were similar, values of CV p=0.01.summarize data from main stems and tillers.

gen treatments in triticale, which was the opposite gen effects on shoot length and on the length ofthe shoot apex for both triticale [Fig. 5(a)] andin wheat where the variation in spikelet number

increased with development (Fig. 3). We have wheat (data not shown). Interestingly, the effectsof nitrogen fertilization on spikelet number per earshown that nitrogen application hardly affected

the spikelet number per ear in triticale at EorSI were unrelated either to the nitrogen effect onshoot length or to the nitrogen effect on the shoot(Table 2). However, the yearly variation in spikelet

number per ear at EorSI was highest in triticale in apex length for both triticale [Fig. 5(b) and (c)]and wheat (data not shown).the high nitrogen treatment (Fig. 3). We could

establish a positive relationship between the dura-tion of the rapid rate of spikelet initiation and thenitrogen effect on spikelet number at EorSI 4. Discussion(Fig. 4). No such relationship was found forwheat. The variation among years in terms of the The effects of low and high nitrogen supply (0

and 200 kg N ha−1) on spikelet initiation wereeffect of nitrogen fertilization on the number ofspikelets at anthesis could not be explained, con- investigated on the main stem and the first tiller

of triticale and wheat. Although we consideredsidering yearly differences in temperature anddevelopment for both cereals (data not shown). only two cultivars, our results have shown general

differences in the response mechanisms of spikeletinitiation to nitrogen fertilization between triticale3.3. Relationships between nitrogen effects on

spikelet number, shoot and shoot apex length and wheat that were related to the phenologicalperformance and morphological characteristics ofapex differentiation of the two cereals.The relationships between nitrogen effects on

spikelet number, shoot and shoot apex length were The spikelet number per ear in wheat wassignificantly increased due to nitrogen fertilizationanalysed at EorSI. We observed significant

increases in the lengths of the shoot and shoot at EorSI and at anthesis (Table 2). However, intriticale, a significant effect of nitrogen applicationapex due to nitrogen fertilization for both cereals

(data not shown). Not surprisingly, there were on spikelet number was observed only at anthesis(Table 2). Ewert (1996) showed that spikelet initia-significant positive relationships between the nitro-


spring in the low nitrogen treatment than wheatplants. An earlier start of development associatedwith earlier utilization of soil water and nitrogenin spring can be advantageous for triticale com-pared to wheat in adaptation to environmentallymarginal conditions (Gawlik and Seiffert, 1990;Karpenstein-Machan and Heyn, 1992).

Spikelet abortion was observed after EorSI inboth nitrogen treatments of wheat and in the lownitrogen treatment of triticale, whereas spikeletinitiation continued at a low rate after EorSI inthe high nitrogen treatment of triticale (Table 2).In wheat, the date of EorSI is close to the stageof development of ‘terminal spikelet’ when themaximum number of spikelets per ear is set.Similar to rye, no such development stage wasobserved for the present cultivar of triticale.Clearly, under the present conditions, nitrogenapplication was more important for the late periodthan for the early period of spikelet initiation intriticale. Honermeier et al. (1989) reported fortriticale (cv. Grado) that late N applications undergood growing conditions promoted assimilatedeposition, especially to distal spikelets, andincreased the grain number per spike.

Less spikelets were initiated on tillers than onmain stems (Table 2). However, no significantdifferences in the effects of nitrogen fertilizationon spikelet number between the two tiller groupswere observed for triticale or wheat (Table 1). Thisis consistent with other results ( Whingwiri andKemp, 1980; Frank and Bauer, 1982) reportingthat nitrogen effects were similar on main stemsand tillers in wheat.

Nitrogen fertilization effects on the variation inspikelet initiation were different for the two cereals(Fig. 3). The spikelet number per ear was moststable in triticale in the treatment without anyadditional nitrogen application (Fig. 3), whichsupports the view that triticale is advantageous inFig. 5. Relationships between the effects of nitrogen fertilization

(N200/N0) on (a) shoot apex length and shoot length, (b) spikelet low-input systems ( Karpenstein-Machan et al.,number per ear and shoot length and (c) spikelet number per 1994). From our results (Table 2, Fig. 3) we con-ear and apex length at EorSI for main stems ($) and tillers (6) clude that spikelet initiation in triticale was betterof winter triticale (cv. Grado). Data are from 4 years of experi-

adapted to low nitrogen conditions than in wheat.mentation 1987–1991. ** Significant at p=0.01.However, our results also indicate that nitrogenapplication can increase the spikelet number intion started earlier in triticale than in wheat. This

might explain the fact that triticale plants could triticale. This, however, strongly depends on theseason (Fig. 4) and, thus, demands flexible man-make better use of the soil nitrogen available in


Darwinkel, A., 1983. Ear formation and grain yield of winteragement of the timing and rate of nitrogenwheat as affected by time of nitrogen supply. Neth. J. Agric.fertilization.Sci. 31, 211–225.

In the present experiment, the shoot length and Ewert, F., 1994. Ertragsphysiologische Untersuchungen anapex length of triticale and wheat varied among Wintertriticale (Triticosecale Wittmack) und Winterweizen

(Triticum aestivum L.) unter besonderer Berucksichtigungyears and nitrogen treatments. We could establishder Ausbildung von Ertragsanlagen — ein Beitrag zura relationship between the effect of nitrogen fertil-Ertragsmodellierung bei Getreide. Dissertation, Universityization on the length of the shoot apex and theof Rostock.

nitrogen effect on shoot length for triticale Ewert, F., 1996. Spikelet and floret initiation on tillers of winter[Fig. 5(a)] and wheat (data not shown). This is triticale and winter wheat in different years and sowing

dates. Field Crops Res. 47, 155–166.consistent with Abbate et al. (1995), who reportedEwert, F., Porter, J., Honermeier, B., 1996. Use of AFRC-that responses of spike growth rate to nitrogen

WHEAT2 to predict the development of main stem andsupply in wheat were related to responses of croptillers in winter triticale and winter wheat in North East

growth rate to nitrogen supply. However, no such Germany. Eur. J. Agron. 5, 89–103.relationships were observed between nitrogen Frank, A.B., Bauer, A., 1982. Effect of temperature and fertil-

izer N on apex development in spring wheat. Agron.effects on grain number and spike growth (AbbateJ. 74, 504–509.et al., 1995). Our results [Fig. 5(b) and (c)] provide

Gawlik, J., Seiffert, M., 1990. Entwicklungsverlauf ausgew-evidence that apex differentiation on the one handahlter Wintertriticaleformen im Vergleich zu Winterweizen-

and apex and shoot growth on the other hand und Winterroggensorten. Arch. Acker-Pflanzenbaudiffer in their response to nitrogen fertilization. Bodenkd. 34, 337–345.

Honermeier, B., Seiffert, M., Ewert, F., 1989. Zum Einfluß derThus, the supply of nitrogen should be consideredStickstoffernahrung auf die Ahrenausbildung von Winter-when analysing and establishing relationshipstriticale. Wiss. Z. Univ. Rostock 38 (3), 9–10.between growth and differentiation processes.

Hunt, L.A., Chapleau, A.M., 1986. Primordia and leaf pro-duction in winter wheat, triticale and rye under field condi-tions. Can. J. Bot. 64, 1972–1976.

Karpenstein-Machan, M., Heyn, J., 1992. Yield structure of theAcknowledgements winter cereals wheat and triticale at climatically marginal

sites in north Hessen. Agribiol. Res. 45, 88–96.Karpenstein-Machan, M., Honermeier, B., Hartman, F., 1994.F. Ewert thanks Mrs Gulzow for the dissections

Triticale. Production Aktuell. DLG-Verlag, Frankfurt/of plants. This research was funded by theMain. 144 ppUniversity of Rostock, Germany.

Langer, R.H.M., Liew, F.K.Y, 1973. Effects of varying nitrogensupply at different stages of the reproductive phase on spike-let and grain production and on grain nitrogen in wheat.Aust. J. Agric. Res. 24, 647–656.

References Whingwiri, E.E., Kemp, D.R., 1980. Spikelet development andgrain yield of the wheat ear in response to applied nitrogen.Aust. J. Agric. Res. 31, 637–647.Abbate, P.E., Andrade, F.H., Culot, J.P., 1995. The effects of

radiation and nitrogen on number of grains in wheat. Zadoks, J.C., Chang, T.T., Konzak, C.F., 1974. A decimal codefor the growth stages of cereals. Weed Res. 14, 415–421.J. Agric. Sci., Camb. 124, 351–360.

spikelet initiation of winter triticale and winter wheat in response to nitrogen fertilization

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