temperature effect on maize germination and root elongation

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Temperature Effect on Maize Germination And Root Elongation Temperature Effect on Maize Germination And Root Elongation

Omar Nazhan Ali

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Temperature effect on maize germination and root elongation

By TITLE PAGE

Omar Nazhan Ali

A Dissertation Submitted to the Faculty of Mississippi State University

in Partial Fulfillment of the Requirements for the Degree of Doctor of Philosophy

in Agronomy in the Department of Plant and Soil Sciences

Mississippi State, Mississippi

August 2018

Copyright by COPYRIGHT PAGE

Omar Nazhan Ali

2018

Temperature effect on maize germination and root elongation

By APPROVAL PAGE

Omar Nazhan Ali

Approved:

____________________________________ W. Brien Henry

(Major Professor)

____________________________________ Richard Harkess

(Committee Member)

____________________________________ Ted Wallace

(Committee Member)

____________________________________ Bennie Keith

(Committee Member)

____________________________________ Michael S. Cox

(Committee Member and Graduate Coordinator)

____________________________________ J. Mike Phillips

(Department Head)

____________________________________ George M. Hopper

Dean College of Agriculture and Life Sciences

Name: Omar Nazhan Ali ABSTRACT

Date of Degree: August 10, 2018

Institution: Mississippi State University

Major Field: Agronomy

Major Professor: W. Brien Henry

Title of Study: Temperature effect on maize germination and root elongation

Pages in Study 66

Candidate for Degree of Doctor of Philosophy

Early planting is one technique to avoid or reduce heat and drought problems that

negatively affecting grain crop production. If producers adopt early planting, cold

temperatures may negatively affect corn yield. It is important to select hybrids that are

suited for planting earlier in the southern United States. Experiments were conducted by

imposing low temperatures during seed germination. Twenty commercially available

corn hybrids were evaluated for seed germination and root elongation. The first objective

was: 1) To determine if some hybrids germinate better at cooler temperatures than others;

and 2) Determine variation in root elongation at cold temperatures among commercially

available hybrids. Corn hybrids varied significantly for seed germination and root traits

under cold temperatures. Some hybrids have significantly surpassed others in seed

germination traits, and they germinated earlier as well having longer radicle length. Also,

there were significant differences across temperatures for all traits measured. A second

objective was: 1) To quantify the effects of cold temperature on seed germination rate; 2)

To evaluate the effects of different cold temperatures on seed germination behavior of

corn hybrids under laboratory conditions to determine how fast they germinated; and

3) To classify hybrids for response to cold temperature using cumulative seed

germination. The results showed that standard germination performance occurred at 10ºC

for all hybrids, but these hybrids performed well under other cold treatments (7.2°C and

8.6° C). There were no significant differences between early hybrids 93 to 105 RM

(Relative Maturity) and full season 115 to 120 RM in germination % and rate in both

experiments, suggesting hybrid genetics played a larger role than relative maturity (early

or late). Therefore, temperature had a major influence on seed germination parameters.

These findings are useful for hybrid selection with respect to cool soil temperature

conditions during early planting.

iii

DEDICATION

I would like to dedicate this work to my parents who guided and gave me the

encouragement to follow in what I believe.

And my loving wife and son.

I dedicate this work to all researchers and farmers. It is my hope that the contents

of this dissertation may help future agronomists with future research.

iv

ACKNOWLEDGEMENTS

I am very appreciative to my major professor Dr. Brien Henry for all of the

support before, throughout, and after of the experiments. He has been an astounding

supervisor. I would like to thank my committee members Dr. Michael Cox, Dr. Richard

Harkess, Dr. Ted Wallace, and Dr. Bennie Keith, for their expertise, knowledge, and

guidance into this research. I appreciate Mississippi State University for providing the

facilities to conduct the research. Thanks also to Dr. Raja Reddy, Dr. Brian Baldwin, and

Dr. Jac Varco for providing additional advice and support in my research. Thanks for the

seed germination lab in Mississippi State, Mr. Fabian Watts, who helped me during the

conduct of this research project. Also, I would like to thank my sponsor, the Iraqi

Ministry of Higher Education and Scientific Research for giving me a scholarship. I

would also like to thank fellow graduate students, Joey, Bryan, Salah, Firas, Abdullah,

Riadh, Chathu, and Singh for their help.

v

TABLE OF CONTENTS

DEDICATION ................................................................................................................... iii

ACKNOWLEDGEMENTS ............................................................................................... iv

LIST OF TABLES ............................................................................................................ vii

LIST OF FIGURES ........................................................................................................... ix

CHAPTER

I. TEMPERATURE EFFECT ON MAIZE GERMINATIONAND ROOT ELONGATION.........................................................................................1

Introduction ...........................................................................................................1

Importance of corn ..........................................................................................1 Planting Early..................................................................................................2

Cold Temperature ...........................................................................................3 Seed Germination............................................................................................6 Hybrids ............................................................................................................7

Literature Cited ....................................................................................................11

II. IMPACT OF SUB-OPTIMAL TEMPERATURES ON CORN ROOT ELONGATION AND DEVELOPMENT ..............................................16

Abstract: ..............................................................................................................16

Material and Methods: .........................................................................................17 Standard germination test: ............................................................................20 Measurements of germination and root traits: ..............................................20

Seed germination tests: .................................................................................21 Radicle length: ..............................................................................................21 Root length: ...................................................................................................22 Root weight: ..................................................................................................22

Field seed emergence: ...................................................................................22 Statistical analysis: ........................................................................................23

Results and Discussion: .......................................................................................23

Germination percentage of corn hybrids regarding to cold temperature: ..............................................................................................23

Impact of cold temperature on radicle length (mm) of corn hybrids: ...........32 Impact of cold temperature on root length (cm) of corn hybrids:.................34

vi

Root weight (g) differs under different cold temperatures: ..........................37

Field validation of seed emergence of corn hybrids planted in cool growing conditions: ..................................................................................39

Conclusions: ........................................................................................................43 Literature Cited: ...................................................................................................44

III. CORN HYBRIDS SEED GERMINATION RESPONSES TO COLD TEMPERATURE ...................................................................................45

Abstract: ..............................................................................................................45 Material and Methods: .........................................................................................46

Measurements of germination characteristics:..............................................48 Maximum seed germination (MSG): ............................................................48 Time to 50 % Germination (T50):..................................................................48

Seed germination rate (SGR): .......................................................................49 Germination velocity index (GVI): ...............................................................49

Statistical analysis: ........................................................................................49 Results and Discussion: .......................................................................................50

Maximum seed germination (MSG): ............................................................50 Time to 50 % Germination (T50):..................................................................55 Seed germination rate (SGR): .......................................................................56

Germination velocity index (GVI): ...............................................................58 Conclusions: ........................................................................................................60

Literature Cited: ...................................................................................................62

IV. DISSERTATION CONCLUSIONS ...................................................................64

vii

LIST OF TABLES

2.1 Twenty corn hybrids from DeKalb and Pioneer seed companies with hybrid name and relative maturity. ......................................................19

2.2 Analysis of variance across the hybrids and temperature treatments and their interaction of germination and root traits. ............................24

2.3 Effect of cold temperature treatments on seed germination percentage at 7 DAP (% SG 7) of 20 corn hybrids. ...............................................25

2.4 Effect of cold temperature treatments on seed germination percentage at 14 DAP (% SG 14) of 20 corn hybrids. ...........................................27

2.5 Effect of cold temperature treatments on seed germination percentage at 21 DAP (% SG 21) of 20 corn hybrids. ...........................................30

2.6 Effect of cold temperature treatments on radicle length (mm) after 14 days (RL 14) of 20 corn hybrids. .........................................................33

2.7 Effect of cold temperature treatments on root length (cm) after 21 days (RL 21) of 20 corn hybrids. .................................................................35

2.8 Effect of cold temperature treatments on root weight (g) after 21 days (RW 21) of 20 corn hybrids. ................................................................38

2.9 Analysis of variance across the hybrids and emergence rate treatments and their interaction for field seed emergence. ....................................41

2.10 Effect of planting early on (FSE) field seed emergence (number of seedling / row) of 20 corn hybrids. ......................................................42

3.1 Four corn hybrids from DeKalb and Pioneer seed companies with hybrid name and relative maturity. ......................................................47

3.2 Analysis of variance across the hybrids and temperature treatments and their interaction of maximum seed germination percentage (MSG %), time to 50 % Germination (T50), seed germination rate (SGR), and germination velocity index (GVI). ............................51

viii

3.3 Effect of cold temperature treatments on maximum seed germination (MSG), time to 50 % germination (T50), seed germination rate (SGR), and germination velocity index (GVI) of four corn hybrids..................................................................................................52

ix

LIST OF FIGURES

2.1 Germination percentage comparison among 20 corn hybrids under three cold temperature treatments at 7 DAP. .......................................26

2.2 Germination percentage comparison among 20 corn hybrids under three cold temperature treatments at 14 DAP. .....................................29

2.3 Germination percentage comparison among 20 corn hybrids under three cold temperature treatments at 21 DAP. .....................................31

2.4 Radicle length (mm) under three cold temperature treatments after 14 DAP......................................................................................................34

2.5 Root length (cm) under three cold temperature treatments after 21 DAP......................................................................................................36

2.6 Root weight (g) differs among corn hybrids under three cold temperature treatments after 21 DAP. .................................................39

2.7 Seed emergence rate (number of seedlings / plot) for the field validation experiment of corn hybrids planted in cool growing conditions after 14, 15, and 16 DAP. ...................................................41

3.1 Influence of cold temperature on maximum seed germination (MSG) of four corn hybrids (DeKalb 42-37, DeKalb 69-29, Pioneer 0339, and Pioneer 2089). The points are recorded MSG % and fitted lines among them. .......................................................................53

3.2 Germination time course of four corn hybrids (DeKalb 42-37, DeKalb 69-29, Pioneer 0339, and Pioneer 2089) response to three levels of cold temperatures treatment (standard 10°C, low 8.6°C, and very low 7.2°C). .................................................................54

3.3 Influence of cold temperature on time to 50 % germination / days (T50) of four corn hybrids (DeKalb 42-37, DeKalb 69-29, Pioneer 0339, and Pioneer 2089). The points are recorded T50 and fitted lines among them. ................................................................................56

x

3.4 Influence of cold temperature on seed germination rate / days (SGR) of four corn hybrids (DeKalb 42-37, DeKalb 69-29, Pioneer 0339, and Pioneer 2089). The points are recorded SGR and fitted lines among them. .......................................................................58

3.5 Influence of cold temperature on germination velocity index (GVI) of four corn hybrids (DeKalb 42-37, DeKalb 69-29, Pioneer 0339, and Pioneer 2089). The points are recorded GVI and fitted lines among them. ................................................................................60

1

CHAPTER I

TEMPERATURE EFFECT ON MAIZE GERMINATIONAND ROOT ELONGATION

Introduction

Importance of corn

Corn or maize (Zea mays L.) is one of the most important, strategic grain crops,

belonging to the Poaceae family grasses. Corn ranks third in importance for cereal crops

in row crops behind rice and wheat. It used both as a staple food for humam consumption

and for animal feed in most developing countries (Akande and Lamidi, 2006; Olakojo et

al., 2007). Corn is predominantly grown in areas with rain fall between 400 to 900 mm

and temperature of 20 to 30°C. (Poehlman, 1983). Major corn producers include the

United States, China, France, India, Canada, Argentina, Spain, Romania and Yugoslavia

(Elyounis et al., 1987). Corn is not only an important human food source and a basic

element of animal feed, but a raw material for the manufacture of many industrial

products.The Products include corn starch, corn oil, corn syrup and products of the

fermentation and distillation industries. Corn derived ethanol has recently been used as a

biofuel (Tilman et al., 2006).

Corn is a versatile crop and can grow over a wide geographic range and a variety

of climatic zones. The suitability of corn to grow in multiple environments is unmatched

by other cereal crops. It is grown in rainfall areas with 250 to 5000 mm per year, and

between 58°N to 40°S latitudes of below sea level to higher than 3000 m. (Dowswell et

2

al., 1996). Low temperature during early growth is one of the major environmental

factors limiting corn range of adaptation (Cutworth and Shaykewich, 1990). Cold soils

during germination and early growth can be a constraint, particularly under minimum

tillage management, a practice that can lower soil temperature during the planting season

by as much as 6°C (Johnson and Lowery, 1985; Graven and Carter, 1991). Germination

and growth in cold soils also allows corn to flower earlier in the summer thus potentially

avoiding droughts that frequently occur mid to late-summer months. Chilling sensitive

plants exhibit several symptoms, among which reduced germination is one of the most

important (Hodges et al., 1997).

Planting Early

Early season corn planting is one of the best strategies to stabilize corn yield by

avoiding high temperatures during the critical grain filling period throughout the US corn

production region (Lauer et al., 1999). Early planting is preferred by producers because it

allows corn plants to grow well and reduces the incidence of insects and aphids. In the

US, planting after April in the midsouth region results in a marked decrease in yield.

Yield reduction is partially attributed to disease and the pests mentioned above, but also

from heat and drought. Previous research from 1982 to 1998 indicated there is a

relationship between climate variation and the production of corn grown in the United

States. Lobell and Asner (2003) reported that every 1°C rise in temperature leads to a 17

% decrease in yield. High temperature has a negative effect on physiological plant

function. A transpiration rate increases, it reduces root activity, decreases absorption of

water, and the plants wilt. High temperature also affects flowering and pollen vitality,

reducing pollen germination rate and fertilization rate, resulting in loss of productivity.

3

Therefore, producers resort to planting early as an avoidance technique to escape the hot

summer and to have greater rainfall opportunities which help to improve plant growth

and increase production, while reducing risk.

Planting early with uniform seed germination and stand establishment would help

to attain high synchronization of the reproductive stages and to reach maturity before the

occurrence of harsh conditions (Subedi and Ma, 2005). The synchronization between

anthesis and silking is essential for success in corn hybrid production (Nagar et al., 1998).

Seed germination is affected by internal factors such as the seed coat, embryo maturity or

chemical inhibitors that induce seed dormancy (Agrawal and Dadlani, 1995). There are

several successful models or measures and criteria that have be used to measure seed

germination performance used to study the physiology of seeds. These include measuring

the maximum seed germination (MSG), seed germination rate (SGR), and time to reach

50% germination in response to cold temperature treatments for radicle emergence

among hybrids. Highly significant differences were observed for seed germination rate,

mean germination time, and germination velocity index (GVI) (Dolapo and Modi, 2015).

They showed that flat seeds germinated faster than round seeds at constant temperatures.

Small seeds had higher germination speed than large seeds. Dezfuli et al. (2008) observed

significant differences in seed germination, early growth, time to 50% germination and

final germination percentage in two corn genotypes.

Cold Temperature

Early planting may affect corn negatively. Cold soil temperatures at the time of

planting can lead to delayed seed germination, reduced seedling vigor and growth under

extreme conditions, and potential frost damage. Therefore, it is important to evalute the

4

performance of hybrids at early planting dates, so producers can select the best hybrid

characterized by its cold tolerance and high productivity to create and develop canopy to

maximize production. Temperature is a major factor that affects growth and development

processes in corn. Higher temperatures increase various biochemical and physiological

processes such as above ground biomass, below ground biomass, crop maturity,

respiration, transpiration, photosynthesis, flowering, and dormancy. Conversely, cold

temperatures reduce the activity of these processes especially during seed germination,

seedling stage, and later during tasselling. Corn is affected by high temperature

disproportionately more during reproductive stages compared to during vegetative stages.

Temperature heavily influences yields. Corn grows best at temperatures ranging from

28°C to 32°C throughout the entire season, although there seems to be variation among

germplasm and commercially available hybrids in tolerance to severe low temperatures

(Wijewardana et al., 2015). Selective breeding strategies have identified germplasm

exhibiting varying degrees of adaptation to germination at cool temperatures (Soldati et

al., 1999; Tollenaar and Lee, 2002). The adaptation of corn to early season planting

requires a higher rate of emergence and vigorous seedling growth under cold

temperatures (Stone et al., 1999). Temperature response in corn varies across hybrids.

The identification of hybrids capable of more rapid growth at low temperatures may

result in earlier canopy development and closure, and increased competition against

weeds, earlier maturity, and grain filling before the high temperatures of long days of late

summer (Pendleton and Egli, 1969). The critical temperature for corn growth depends

upon the soil temperature during early developmental stages (Richner et al., 1996) and

ranges from 10°C to 17°C depending on the hybrid trait package and the germplasm

5

(Bowen, 1991; Haldimann et al., 1996). Temperature tolerance can be verified by

screening genotypes at either low or high temperatures or both. Corn is highly susceptible

to frost damage, especially beyond V5 to V6 (~30 cm) because the growing point has

moved from below the soil surface to above-ground. According to Carter and Hesterman

(1990), the lethal damage to corn stem, leaf, and ear occurs if the temperature is below -

2.2°C for a few minutes and below 0°C for more than four hours. Conversely,

temperatures over 45°C cause irreversible damage to corn plant tissue (Sinsawat et al.,

2004).

Temperature is a major environmental factor that affects seed germination rate. It

affects three processes which are the germination process itself, seed deterioration, and

dormancy loss (Hsu et al., 1984; and Roberts, 1988). Sub-optimal soil temperatures at

seeding affects the germination rate and maximum seed germination. Using mathematical

functions to determine temperature effects on seed germination may be useful in

evaluating germination characteristics or establishment potential among hybrids (Jordan

and Haferkamp, 1989). Seed vigor is a result of final seed germination percentage and

germination rate and are both considered sensitive indicators (Ellis, 1980). Germination

can be characterized and occurs in three cardinal temperatures (minimum, maximum, and

optimum) that represents a range of germination temperatures. Because minute

differences in temperatures can cause considerable differences in germination time, the

minimum temperatures are critical for accurate phenological predictions. Gardner et al.

(1984) explained that the minimum temperature ranges in which corn seeds germinate are

8-10°C, the ideal is 32-35°C, and the maximum is 40-44°C. Germination rate of all seeds

of different crops slow down at low temperatures, as some of these types of seeds are

6

very sensitive to the low temperature, especially during saturation with water. Heyne and

Laude (1940) reported that the lowest temperature suitable for the germination of corn

seeds is 10°C. Elyounis et al. (1989) asserts that if soil temperature is between 16-18°C,

it increases the speed of germination, especially the emergence of seedlings, and when

the soil temperature is about 20°C, the emergence of the seedling takes 5-6 days after

planting the seeds. Depending on the temperature conditions, the speed of germination is

important for establishing uniform seedling stands (Dolapo and Modi, 2015).

Seed Germination

Seed germination is the restoration of the dormant embryo to its activity and

growth once appropriate conditions are available. Germination begins by imbibing the

seed with water, which leads to the softness of the seed coat and increases the embryo

size, which presses on the seed coat and tears it and the small plant emerges from outside

the seed (Bewley and Black, 1994). The seedling grows based on the food stored in the

seed until the shoot emerges and green leaves form, the roots grow enough in the soil,

and it becomes able to rely on itself to form its food. This stage of the plant life is known

as the seedling. Seedling growth begins with the appearance of the radicle, which grows

down under the influence of gravity, forming the primary root from which secondary

roots appear later (Barroco et al., 2005). In general, seed germination requires appropriate

environmental conditions before initiating germination. These include water, oxygen,

appropriate temperature, light, seed maturity, and embryo vitality. Seeds vary widely in

terms of the proper temperature for germination, and if there are no other specific factors,

seeds germinate in a particular temperature range. The seeds of temperate plants

germinate in a lower thermal range than which tropical plants germinate. Corn seeds (a

7

subtropical plant) grow between 10 - 45°C, and it is difficult to determine a certain

temperature as the optimum temperature because this degree varies according to other

prevailing environmental conditions (Ritchie et al., 1993; and Miles and Brown, 2007).

Germination is an important and sensitive stage of the plant development, and it is

the first stage of a plant’s life cycle (De Villiers et al., 1994). Among the stages of the

plant life cycle, seed germination and emergence are major processes in the plant growth

(Hadas, 2004). Seed germination begins with imbibition of water and is considered to be

completed with the initiation of embryo growth. The embryo causes a change in seed

water content and coincides with radicle elongation (Bradford, 1990). Seeds imbibe a

certain amount of water from external sources to initiate radicle emergence. After the

emergence of the structures surrounding the embryo by the radicle, germination becomes

visible. When the equilibrium occurs between the seed water potential and its

surroundings, which is affected by various environmental and physiological factors, the

radicle emerges. The factors that control these processes include temperature, soil

moisture, seed quality, planting depth, seed size, and soil type (Lee et al., 1998; Krishnan

et al., 2011; Seepaul et al., 2012).

Hybrids

Selecting corn hybrids with high emergence potential and strong growth

characteristics in cold soils is an important objective in temperate regions (Eagles, 1990).

Cold tolerance at germination is a polygenic trait (Eagles, 1982; Eagles, 1988; Landi et

al., 1992; Kollipara et al., 2002). The identification of the main genes responsible for cold

tolerance and cold-acclimation would provide potential new information which could be

usefully integrated into a producer’s hybrid selection (Thomashow, 1999). Studies of

8

various stress tolerances suggest exposure to desiccation stress improves tolerance to

freezing (Huitema et al., 1982; Vigh et al., 1986). There are different instances in which a

reaction to a type of stress can induce tolerance to another type, such as wounding,

dehydration, low temperature and pest attack (McIntosh et al., 1998; Shinozaki and

Yamaguchi-Shinozaki, 2000). Response to different stresses is often mediated by abscisic

acid (ABA). This hormone is also partly responsible for cold acclimation (Lang et al.,

1989). Simple, consistent, and applicable methods are necessary to evaluate genetic

variability and cold tolerance in crops because temperature tolerance is a multigenic trait

(Reddy et al., 2001). A study carried out on a few corn inbred lines suggested the

presence of genetic variability for cold tolerance at germination, of seeds produced by

plants subjected to a defoliation treatment during maturation (Frascaroli and Casarini,

1999).

Hybrid genotypes typically consist of the integration of two lines. The main goal

of corn breeding is to develop high yielding hybrids. The adaptation of these corn hybrids

to temperate and early season environments is also of great significance to the producer.

The development of a new corn hybrid must consider improve ments in yield,

standability, pest resistance and suitability for cold temperature and early planting.

Producers need corn hybrids with superior cold tolerance during germination and early

growth (Hayhoe et al., 1996). Rapid and consistant emergence is needed across the field

and it is necessary for the seed industry to produce high quality corn seed that does this.

The ability to identify and select cold tolerant hybrids is an important step in this process

because germination under cold stress is influenced by the maternal parent (Queijo,

2012). Seed size and shape are also important characteristics that affect the germination

9

and growth of corn hybrids (Shashdhara et al., 1988). Hybrid germplasm has a significant

effect on the speed of seed germination, but other factors affect the speed of seed

germination under the same conditions. For example, in the experiment conducted by

Popp and Brumm (2003) on five corn hybrids graded as flat and round seeds, they found

that germination and vigor of round seed declined faster than flat seeds, this might be due

to the lower vigor of round seeds as compared to flat seeds.

Growing corn under heat and drought conditions is one of the emerging problems

in the US Mid-South. Heat and drought limit corn productivity in the state of Mississippi,

so it is important to select hybrids suited for planting earlier in the southern United States

(Wijewardana et al., 2015). By planting earlier, producers minimize the probability of

heat and drought negativly influencing the crop. The changes in projected climate in the

US Mid-South will likely increase the risk of prolonged drought conditions, thus

increasing the need for planting early to avoid this problem (Ault et al., 2014). Despite

previous research success on corn breeding and agronomy, a large gap still exists in the

research to assess the variation in response to cold temperatures among corn hybrids

germination in the US Mid-South. This has implications on corn germination and

subsequent growth and development in this region, thus warranting more research on

corn hybrids response to cold conditions. Understanding hybrid response to cold

conditions at germination would help in mitigation of the major problem of delayed and

non-uniform emergence during cold and excessive soil moisture when direct seeding

corn. Also, the identification of cold tolerant corn hybrids would help to ensure

successful seed germination and stand establishment of these commercial hybrids already

in use by producers. The objectives of this study are: 1) To determine if some hybrids

10

germinate better at cooler temperatures than others; 2) Determine variation in root

elongation at cold temperatures among commercially available hybrids; 3) To quantify

the effects of cold temperature on seed germination rate; 4) To evaluate the effects of

different cold temperatures on seed germination behavior of corn hybrids under

laboratory conditions to determine how fast they germinated; and 5) To classify hybrids

for response to cold temperature using cumulative seed germination.

11

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15

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16

CHAPTER II

IMPACT OF SUB-OPTIMAL TEMPERATURES ON CORN ROOT ELONGATION

AND DEVELOPMENT

Abstract:

Corn is a versatile crop grown over a range of agro climatic zones. If producers

adopt early planting to avoid high temperature and drought under rain fed systems, cold

temperatures may negatively affect corn yield. Experiments were conducted by imposing

treatments of low temperatures during seed germination. Twenty commercially available

corn hybrids were evaluated for seed germination and root elongation. Seeds for these

trials were obtained from two industry leading seed companies in 2015 and 2016.

Standard germination assays confirmed all seed germinated at or near 100 percent under

optimal conditions. Each temperature × hybrid treatment was replicated four times in a

completely randomized design with 50 seed per replicate and the experiment was

repeated. Seed were placed on a moistened seed germination paper, rolled, and secured

with rubber bands. The samples were monitored daily to ensure that the filter paper

remained moist. The cold germ test was modified by transferring all samples to a warm

room (20°C) to evaluate cold germination and root elongation. Because the goal is to

plant earlier into potentially wet and cold soil, seed germination at different temperatures

was evaluated with the following objectives: 1. To determine whether some hybrids

17

germinate better at cooler temperatures than others; and 2. To evalute variations in root

elongation at cold temperatures among commercially available hybrids. Corn hybrids

varied significantly for seed germination and root traits under cold temperatures. Some

hybrids significantly surpassed others in seed germination traits, germinating earlier as

well as having longer radicle lengths. Also, there were significant differences across

temperatures for all traits measured. Our data suggests that variability exists among

emergence and vigor at cold temperatures for commercially available hybrids. Producers

who plant early could select a hybrid that performs best at cool temperatures.

Keywords: Corn, Hybrids, Seed germination, Cold temperature treatment, Root

elongation, Root development, Drought avoidance, Heat avoidance.

Abbreviations:

(GP): Germination percentage. (% SG 7): Seed germination percentage after 7

days of planting date. (% SG 14): Seed germination percentage after 14 days. (% SG 21):

Seed germination percentage after 21 days. (RL 14): Radicle length (mm) after 14 days.

(RL 21): Root length (cm) after 21 days. (RW 21): Root weight (g) after 21 days. (FSE):

Field seed emergence. DAP: Days after planting day.

Material and Methods:

Seeds of twenty popular corn hybrids grown commercially in the United States

from DeKalb and Pioneer Seed Companies were used for this study (Table 2.1). This

study was conducted at the seed germination lab at Mississippi State to estimate corn

hybrids seed germination response to cold temperature. The experiment was conducted

by imposing low temperatures during seedling germination. Seeds for these trials were

18

obtained from two premier corn hybrid companies in 2015 and 2016. All seeds were kept

in cold storage to maintain seed quality prior to testing. Standard cold test germination

assays confirmed all seed germinated at or near 100 percent under optimal conditions.

Each temperature × hybrid treatment was replicated four times with 50 seed per replicate

(20 corn hybrids × 3 levels of temperature) standard 10°C, low 8.6°C, and very low

7.2°C. Seed were placed on a 3-layer distilled water-moistened seed germination paper,

rolled, and secured with rubber bands. The samples were monitored daily to ensure that

the filter paper remained moist. Replicates for each hybrid were completely randomized

within the germination chamber for each temperature in order to minimize the potential

of small temperature changes within the chambers. The cold germination test was

modified to further challenge seed at increasingly colder temperatures to evaluate cold

germination potential of commercial hybrid germplasm. After 14 days of the cold test, all

samples were transferred to a warm room (20°C) for 1 week. Germinated seeds were

counted and recorded. A seed was considered germinated with a radicle length of at least

2 mm (Dezfuli et al., 2008; and Dolapo and Modi, 2015).

19

Table 2.1 Twenty corn hybrids from DeKalb and Pioneer seed companies with hybrid name and relative maturity.

Brand Hybrid Relative Maturity

1 DeKalb 42-37 92

2 DeKalb 47-35 97

3 DeKalb 49-29 99

4 DeKalb 50-84 100

5 DeKalb 53-78 103

6 DeKalb 54-38 104

7 DeKalb 55-20 105

8 DeKalb 55-93 105

9 DeKalb 58-06 108

10 DeKalb 60-63 110

11 DeKalb 62-08 112

12 DeKalb 67-57 116

13 DeKalb 69-29 119

14 Pioneer 9329 93

15 Pioneer 0339 103

16 Pioneer 0636 106

17 Pioneer 0843 108

18 Pioneer 1197 111

19 Pioneer 1637 116

20 Pioneer 2089 120

20

Standard germination test:

The standard germination test is the most common test to determine the quality of

seed before planting. It reveals a lot about seed vitality and seedling vigor. The standard

germination test measures the seed’s ability to germinate, but it does not describe the

deterioration and other consequences of seed germination. Because it is conducted under

optimum conditions for seed germination and development, this test often fails to predict

the performance of a seed status under actual field conditions rarely like in the laboratory.

In this study, before the start of the experiment, the standard germination test was

conducted by germinating the 20 commercial corn hybrids used in this study. Four

replicates of 50 seeds from each hybrid were placed on three-layered germination paper

moistened with distilled water according to AOSA (2013) guidelines. The rolled papers

were put in plastic boxes and incubated in a growth chamber with temperature set at

optimum for 1 week. Germinated seeds, seed with radicle emerged greater than 2mm,

were counted and recorded. All corn seed germinated successfully at 20°C, meaning all

seed groups were good quality (Heyne and Laude, 1940; and Gardner et al., 1984). So

that we made it more challenging in this experiment to evaluate our hybrids. Standard

germination test was also conducted by (Dolapo and Modi, 2015; and Queijo, 2012).

Measurements of germination and root traits:

• Seed germination percentage at 7 DAP.



• Radicle length (mm) at 14 DAP.

• Root length (cm) at 21 DAP.

21

• Root weight (g) at 21 DAP.

• Field seed emergence.

Seed germination tests:

Seed germination tests were conducted by placing fifty seeds for each hybrid for

each treatment on a 3-layer moistened seed germination paper, rolled, and secured with

rubber bands, and then placed in plastic boxes (25 × 40 cm). Then, seeds were incubated

in germination chambers (Percival Scientific, Model No I-36LLVL., Perry, Iowa) under

three cold temperatures (7.2°C, 8.6°C, and 10°C), Each treatment was replicated four

times and the experiment was repeated. The samples were monitored daily, and the

germination percentages were calculated at 7 and 14 days after planting. After that, the

samples were transferred to a warm room (20°C) for full germination and root elongation.

The germination percentage was calculated at 21 days from planting day.

Germination percentage (GP) was calculated according to the International Seed

Testing Association (ISTA) method:

GP = Number of normally germinated seeds

Total number of seeds sown × 100 (2.1)

Radicle length:

The radicle length was measured manually by using a ruler in (mm) in the day 14

from the planting date. Ten readings were taken from each sample and the mean radicle

length of each hybrid was determined for each temperature by hybrid under the influence

of different temperatures treatment as in Sozharajan and Natarajan (2013).

22

Root length:

The root length was measured manually by using a ruler from the point of the first

cotyledonary node to the tip of the longest root (cm) in the day 21 from the planting day.

Ten seedlings were randomly selected from each sample and the roots were cut off from

their point of contact with the stem, and the root length of each hybrid was determined

for each temperature by hybrid under the influence of different temperatures treatment as

in Sivakumar and Thamizhiniyan (2012).

Root weight:

The roots were cut off and placed in paper bags and dried at 70°C in hot air oven

for 48 hours or until a stable weight. After drying, root weights were measured with an

electronic balance in (g).

Field seed emergence:

The study was conducted at Mississippi State University in the 2016 growing

season. Two factors were used for this study: 20 Hybrids planted at 35,000 plants / acre

with emergence measured over three days (14, 15 and 16 days after planting). Plots were

arranged in a randomized complete block design with four replicates. Individual plots

were four rows wide at 12.5’ × 30’, and 2 - 2.5” planting depth.

Seeds were planted in one planting date which was on March 17, representing a

very early for the region. After planting, the soil temperature was 8.6°C at 2” deep, so it

was initially cold. Field emergence data were recorded by counting the number of

emerged seedlings per row (Two middle rows per plot were counted) at 14, 15, and 16

days after planting (Queijo, 2012).

23

Statistical analysis:

The design of experiment was a completely randomized design with four

replications for each hybrid by temperature treatment. The seed parameters were

analyzed using one-way ANOVA procedure (PROC GLM, SAS 9.4, SAS Institute 2013,

Cary, NC, USA), with the hybrids and temperature considered as sources of variance.

Data were subjected to analysis of variance for seed germination percentages after 7, 14,

and 21 days, radicle length (mm) after 14 days, root length (cm) after 21 days, root

weight (g) after 21 days, and field seed emergence. Treatment means were separated

using Fisher’s Protected least significant difference test (LSD; P ˃ 0.01). The supporting

field trial was a RCBD with four replicates and was conducted a single time in 2016.

The seed germination experiment was repeated twice, and there was similarity

between the two experiments. The data were combined and analyzed together and

presented.

Results and Discussion:

Germination percentage of corn hybrids regarding to cold temperature:

With the advanced technology in seed breeding, genetic traits modification, and

crop management, the productivity of corn has been improved. As recently reported, it

would be more beneficial to plant seeds early in the Mid-south region in the US to avoid

the extreme weather conditions of summer during the grain-filing period. However, with

the unpredictable early spring weather conditions during seed germination phase, early

planting has exhibited challenges. Here in this part of the research, germination

24

percentage of 20 corn hybrids in three different cold temperature settings was tested

(7.2°C, 8.6°C, and 10°C) at 7, 14, and 21 days of germination after planting day.

The analysis of variance indicates that there were significant differences among

temperatures, among hybrids, and their interactions as well in the traits of germination

percentage 7 DAP, 14 DAP, and 21 DAP (Table 2.2).

Table 2.2 Analysis of variance across the hybrids and temperature treatments and their interaction of germination and root traits.

Source % SG 7 % SG 14 % SG 21 RL 14 RL 21 RW 21

TEMP *** *** *** *** *** ***

HYB *** *** * *** *** ***

TEMP × HYB *** *** * *** *** ***

*, **, *** Significantly different at 0.05, 0.01 and 0.001 probability levels, respectively. NS: non-significant at P > 0.05.

Table (2.3) shows that there were significant differences among corn hybrids for

% SG 7 DAP in response to cold temperature treatments. DeKalb 67-57 showed the

highest average germination percentage (95.3 %), while Pioneer 1637 gave the lowest

(35.4 %). Also, temperatures varied significantly in this trait, so that 10°C had the highest

average (98.3 %), while 7.2°C recorded the lowest average germination percentage (32.0

%). In this study, significant interactions were observed between temperatures and

hybrids. DeKalb 53-8, DeKalb 67-57, and Pioneer 1197 at 10°C showed the highest

germination percentage (100.0 %) after 7 DAP.

25

Table 2.3 Effect of cold temperature treatments on seed germination percentage at 7 DAP (% SG 7) of 20 corn hybrids.

Hybrids Temperatures

Average 7.2°C 8.6°C 10°C

DeKalb 42-37 4.5 k 86.3 cd 98.5 ab 63.1 e

DeKalb 47-35 23.8 ij 84.3 cd 97.3 abc 68.4 d

DeKalb 49-29 7.8 jk 85.0 cd 96.5 bc 63.1 e

DeKalb 50-84 48.3 h 99.5 a 99.3 a 82.3 c

DeKalb 53-78 82.8 d 98.5 ab 100.0 a 93.8 a

DeKalb 54-38 27.5 i 84.3 cd 99.8 a 70.5 d

DeKalb 55-20 84.5 cd 97.3 abc 99.8 a 93.8 a

DeKalb 55-93 71.5 e 95.3 bc 99.3 a 88.7 b

DeKalb 58-06 4.3 k 72.0 e 98.8 ab 58.3 g

DeKalb 60-63 85.3 cd 96.8 bc 99.8 a 93.9 a

DeKalb 62-08 87.3 cd 99.3 a 99.8 a 95.4 a

DeKalb 67-57 86.8 cd 99.3 a 100.0 a 95.3 a

DeKalb 69-29 10.3 j 99.3 a 99.5 a 69.7 d

Pioneer 9329 1.0 m 67.3 f 95.0 bc 54.4 h

Pioneer 0339 1.3 m 81.5 d 98.0 ab 60.3 g

Pioneer 0636 0.5 n 56.0 g 99.0 ab 51.8 i

Pioneer 0843 0.3 n 18.5 ij 97.3 abc 38.7 j

Pioneer 1197 2.8 l 83.5 d 100.0 a 62.1 ef

Pioneer 1637 3.3 l 7.0 jk 96.0 bc 35.4 k

Pioneer 2089 7.0 jk 19.5 ij 93.3 bcd 39.9 j

Average 32.0 c 76.5 b 98.3 a 69.0 Values are means of 4 replicates. Means separation within temperature or hybrid averages, and means within temperature × hybrid with the same letters are not significantly different at P > 0.01 using LSD.

26

Seed germination percentage among hybrids DKC 42-37, DKC 49-29, DKC 58-

06, DKC 69-29, PHB 9329, PHB 0339, PHB 0636, PHB 0843, PHB 1197, PHB 1637,

and PHB 2089 were lower than 10 %, followed by DKC 47-35 about 24 % and DKC 54-

38 about 28 %. Hybrids DKC 53-78, DKC 55-20, DKC 60-63, DKC 62-08, and DKC 67-

57 showed above 80 % at 7.2°C for the first 7 days. It seems that germination percentage

of the hybrids PHB 0843, PHB 1637, and PHB 2089 are more susceptible towards cold

temperature with less than 20 % germination even at 8.6°C. As for germination

percentage at 10°C, all the corn hybrids showed higher than 95 % which supports current

recommendations for 10°C as a minimum (Table 2.3 and Figure 2.1). These results are

similar to those of Queijo (2012) and Gardner et al. (1984) who reported the minimum

temperature in which corn seeds germinate is 10°C.

Figure 2.1 Germination percentage comparison among 20 corn hybrids under three cold temperature treatments at 7 DAP.

0102030405060708090

100

% G

erm

inat

ion

Hybrids

% Germination 7 Days

7.2°C 8.6°C 10°C

27




DeKalb 42-37 94.0 ef 97.3 bcd 99.0 ab 96.8 cde

DeKalb 47-35 88.8 h 98.5 abc 99.0 ab 95.4 e

DeKalb 49-29 91.5 gh 98.8 abc 97.5 bcd 95.9 e

DeKalb 50-84 98.0 abc 99.5 ab 99.8 a 99.1 ab

DeKalb 53-78 98.5 abc 100.0 a 100.0 a 99.5 ab

DeKalb 54-38 99.5 ab 98.8 abc 100.0 a 99.4 ab

DeKalb 55-20 97.0 cde 99.0 ab 99.8 a 98.6 abc

DeKalb 55-93 100.0 a 99.3 ab 99.8 a 99.7 ab

DeKalb 58-06 89.2 h 99.8 a 100.0 a 96.3 de

DeKalb 60-63 99.0 ab 100.0 a 99.8 a 99.6 ab

DeKalb 62-08 100.0 a 99.8 a 100.0 a 99.9 a

DeKalb 67-57 100.0 a 100.0 a 100.0 a 100.0 a

DeKalb 69-29 99.5 ab 99.5 ab 99.8 a 98.0 bcd

Pioneer 9329 70.0 k 95.8 abc 99.3 ab 88.3 g

Pioneer 0339 91.8 fgh 99.5 ab 99.3 ab 96.8 cde

Pioneer 0636 55.5 l 98.0 abc 99.3 ab 84.3 h

Pioneer 0843 84.8 i 97.8 bcd 98.0 abc 93.5 f

Pioneer 1197 96.5 de 100.0 a 100.0 a 98.8 ab

Pioneer 1637 75.8 j 95.8 cde 99.0 ab 90.2 g

Pioneer 2089 85.0 i 94.8 def 98.0 abc 92.6 f

Average 90.7 b 98.6 a 99.4 a 96.1

Values are means of 4 replicates. Means separation within temperature or hybrid averages, and means within temperature × hybrid with the same letters are not significantly different at P > 0.01 using LSD.

28

At 14 DAP of cold temperature treatment (Table 2.4), there were significant

differences among corn hybrids for seed germination percentage. DKC 67-57 showed the

highest average of germination percentage (100.0 %) at 14 DAP, while hybrid Pioneer

0636 had the lowest percentage (84.3 %). The results of the same table confirmed that

there were significant deferences among the three levels of cold temperatures. The

standard (10°C) recorded a higher value of germination (99.4 %), but the very cold

treatment had (90.7 %). The factors of this study had significant interaction, so hybrids

DeKalb 55-93 and DeKalb 62-08 at 7.2°C recorded (100.0 %). DeKalb 60-63 at 8.6°C

and DeKalb 53-78 and Pioneer 1197 under both 8.6°C and 10°C recorded (100.0 %), and

DeKalb 54-38, DeKalb 58-06, and DeKalb 62-08 at 10°C gave also (100.0 %)

germination after 14 DAP. While DeKalb 67-57 had (100.0 %) at all temperature

treatments.

In this study, seed germination percentages at 14 DAP were higher than 80 %

under 7.2°C for most of the hybrids, which indicates that low temperature effects are

bridged by the length of germination period. Seed germination percentage was high at

8.6°C and 10°C after 14 DAP (Figure 2.2).

29


The effect of cold temperature treatments on seed germination percentage at 21

DAP of 20 commercial corn hybrids is shown in (Table 2.5). The % SG 21 varied

significantly among the hybrids with the exception of the LSD (P > 0.01). Temperatures

also differed significantly in this trait, and the hybrids × temperatures potential

interaction was significant as well. These results shown in this table confirmed that all

seed germinated at or near 100 percent after 21 DAP. The above results are in agreement

with observations of Wijewardana et al., (2015).

0102030405060708090

100

% G

erm

inat

ion

Hybrids


7.2°C 8.6°C 10°C

30




DeKalb 42-37 94.0 g 97.8 def 99.0 bcd 96.9 g

DeKalb 47-35 98.0 def 99.5 ab 99.8 ab 99.1 de

DeKalb 49-29 97.3 ef 99.0 bcd 99.0 bcd 98.4 ef

DeKalb 50-84 99.8 ab 100.0 a 100.0 a 99.9 ab

DeKalb 53-78 99.3 abc 100.0 a 100.0 a 99.8 bcd

DeKalb 54-38 99.5 ab 99.3 abc 100.0 a 99.6 bcd

DeKalb 55-20 98.8 bcd 99.3 abc 99.8 ab 99.3 cd

DeKalb 55-93 99.3 abc 99.3 abc 100.0 a 99.5 bcd

DeKalb 58-06 99.5 ab 99.8 ab 100.0 a 99.8 bcd

DeKalb 60-63 100.0 a 100.0 a 100.0 a 100.0 a

DeKalb 62-08 100.0 a 99.8 ab 100.0 a 99.9 ab

DeKalb 67-57 100.0 a 100.0 a 100.0 a 100.0 a

DeKalb 69-29 99.5 ab 99.5 ab 99.8 ab 99.6 bcd

Pioneer 9329 93.8 g 97.0 f 99.5 abc 96.8 g

Pioneer 0339 99.5 ab 99.8 ab 100.0 a 99.8 bcd

Pioneer 0636 100.0 a 99.3 abc 99.5 ab 99.6 bcd

Pioneer 0843 97.0 f 98.0 def 98.5 cde 97.8 f

Pioneer 1197 99.5 ab 100.0 a 100.0 a 99.8 abc

Pioneer 1637 99.3 abc 98.5 cde 99.8 ab 99.2 d

Pioneer 2089 97.3 ef 98.8 cde 99.0 bcd 98.3 f

Average 98.6 b 99.2 a 99.7 a 99.2


31

According to Figure (2.3) which shows the temperature impact on hybrids after

14 days of cold temperature treatment and then warm temperature until 21 days, seed

germination percentages were higher than 97 % for most of treatments. It can be said that

the seed germination percentage of hybrids increased greatly depending on temperature

and by the time of incubation.


0

10

20

30

40

50

60

70

80

90

100

% G

erm

inat

ion

Hybrids


7.2°C 8.6°C 10°C

32

Impact of cold temperature on radicle length (mm) of corn hybrids:

In addition to collecting the germination percentage of the corn hybrids at

different cold temperature treatments, radicle length at 14 days was also measured.

Analyses of variance of this measurement (RL 14) reflected highly significant differences

among the three cold temperature treatments, among hybrids, and their interaction (Table

2.2).

There were highly significant differences for the radicle length among hybrids.

The highest average of this trait (17.95 mm) was observed in hybrid DKC 55-93, while

hybrid PHB 1637 showed lowest average (8.95 mm), the values were recorded in (Table

2.6). These data indicate that there is greater radicle length at standard temperatures

(27.56 mm) than the cold and very cold temperature (1.68 and 10.13 mm) respectively,

possibly due to temperature effects on cell elongation. However, the hybrids varied at

radicle length under each cold temperature (Wijewardana et al. 2015). The higher

interaction was observed in the treatment of 10°C with hybrid DKC 55-93 (39.99 mm).

Results have shown that at 14 days, all the hybrids radicle length at 7.2°C were

below 5 mm and the hybrids PHB9329, PHB0339, PHB0636, PHB0843, PHB1197, and

PHB1637 had no emerged radicle. All the hybrids under the 8.6°C temperature treatment

were longer than 5 mm, whereas, at 10°C, the radical lengths were all above 18 mm

(Figure 2.4).

33

Table 2.6 Effect of cold temperature treatments on radicle length (mm) after 14 days (RL 14) of 20 corn hybrids.



DeKalb 42-37 1.42 wxy 8.61 qrs 21.72 j 10.58 f

DeKalb 47-35 1.14 xy 9.09 qrs 22.67 ij 10.97 f

DeKalb 49-29 0.79 xy 9.60 pqr 20.09 kl 10.16 fg

DeKalb 50-84 2.16 vwx 12.92 o 28.82 fg 14.63 c

DeKalb 53-78 3.28 tuv 8.85 qrs 26.22 h 12.78 de

DeKalb 54-38 3.85 tu 8.28 rs 32.61 bc 14.91 c

DeKalb 55-20 3.68 tuv 8.46 qrs 31.46 cde 14.53 c

DeKalb 55-93 3.90 tu 9.96 pqr 39.99 a 17.95 a

DeKalb 58-06 0.75 xy 8.97 qrs 18.85 lm 9.52 gh

DeKalb 60-63 2.88 uvw 11.09 p 31.62 cde 15.20 c

DeKalb 62-08 4.73 t 16.53 n 30.20 ef 17.15 ab

DeKalb 67-57 3.02 uvw 16.52 n 30.33 def 16.62 b

DeKalb 69-29 1.03 xy 10.12 pq 34.26 b 15.14 c

Pioneer 9329 0.00 y 7.97 s 29.42 fg 12.47 e

Pioneer 0339 0.00 y 9.65 pqr 30.22 ef 13.29 de

Pioneer 0636 0.00 y 8.45 qrs 31.93 cd 13.46 d

Pioneer 0843 0.00 y 9.54 pqr 23.46 i 11.00 f

Pioneer 1197 0.00 y 11.02 p 28.13 g 13.05 de

Pioneer 1637 0.00 y 8.48 qrs 18.37 m 8.95 h

Pioneer 2089 1.00 xy 8.58 qrs 20.88 k 10.15 fg

Average 1.68 c 10.13 b 27.56 a 13.12


34

Figure 2.4 Radicle length (mm) under three cold temperature treatments after 14 DAP.

Impact of cold temperature on root length (cm) of corn hybrids:

The cell division and elongation result in growth, whereas development consists

of new roots initiation and develop into tissues. The results of the statistical analysis

showed that there were significant differences among temperatures, hybrids, and their

interactions as well as for root length (cm) which are presented in the table (2.2).

The root length in general showed variation across treatments. The maximum

average was noted in hybrid PHB 1637 and showed (22.5 cm) after 21 days. The

minimum value was recorded in hybrid Pioneer 9329 and gave the lowest root length

(16.4 cm) (Table 2.7).

0

5

10

15

20

25

30

35

40

Rad

icle

Len

gth

(mm

)

Hybrids

Radicle Length (mm) 14 Days

7.2°C 8.6°C 10°C

35

Table 2.7 Effect of cold temperature treatments on root length (cm) after 21 days (RL 21) of 20 corn hybrids.



DeKalb 42-37 14.2 ef 17.9 d 23.4 ab 18.5 fg

DeKalb 47-35 13.8 f 15.4 e 20.7 bc 16.6 h

DeKalb 49-29 15.1 e 17.7 d 22.1 b 18.3 g

DeKalb 50-84 17.7 d 20.1 bc 24.6 a 20.8 d

DeKalb 53-78 17.7 d 18.5 cd 20.9 bc 19.0 ef

DeKalb 54-38 19.4 c 19.7 c 24.0 ab 21.0 cd

DeKalb 55-20 18.3 cd 18.6 cd 21.1 b 19.3 e

DeKalb 55-93 18.6 cd 19.6 c 24.0 a 20.7 d

DeKalb 58-06 17.3 d 17.9 d 18.5 cd 17.9 g

DeKalb 60-63 18.1 cd 18.6 cd 19.1 c 18.6 fg

DeKalb 62-08 17.6 d 18.4 cd 19.1 c 18.4 fg

DeKalb 67-57 16.9 de 18.2 cd 19.8 c 18.3 g

DeKalb 69-29 18.6 cd 18.9 cd 20.57 bc 19.4 e

Pioneer 9329 15.1 e 16.3 de 17.9 d 16.4 h

Pioneer 0339 19.2 c 20.0 c 22.8 b 20.6 d

Pioneer 0636 19.7 c 20.5 bc 21.5 b 20.6 d

Pioneer 0843 20.1 bc 20.3 bc 22.7 b 21.0 cd

Pioneer 1197 21.3 b 21.8 b 23.8 ab 22.3 ab

Pioneer 1637 21.6 b 21.9 b 24.0 ab 22.5 a

Pioneer 2089 20.3 bc 20.6 bc 24.0 a 21.6 bc

Average 18.0 c 19.0 b 21.7 a 19.6


36

Root length increased at standard temperature and reduced significantly at low

and very low temperature conditions, so the values were (21.7, 19.0, and 18.0 cm)

respectively. Also, significant interaction was noted for temperatures × hybrids, so that

DeKalb 50-84 at 10°C had the longest root average (24.6 cm), while DeKalb 47-35

recorded (13.8 cm). Root length is affected by environmental conditions and by genetics

(Yoshida and Hasegawa, 1982). The root length increase by cell division and elongation,

whereas development controls the period of growth and initiation of new roots (Imran et

al., 2013).

Figure (2.5) shows the root length (cm) under three different cold temperature

treatments after 21 DAP. There were differences identified in root length among corn

hybrids under different temperature. At cold and very cold treatments, the root length of

some hybrids reached to (22 cm), but at 10°C the root length exceeded (24 cm).

Figure 2.5 Root length (cm) under three cold temperature treatments after 21 DAP.

0

5

10

15

20

25

Roo

t Len

gth

(cm

)

Hybrids

Root Length (cm) 21 Days

7.2°C 8.6°C 10°C

37

Root weight (g) differs under different cold temperatures:

Growth and development are two temperature-dependent procedures that

contribute to root system enlargement according to (Imran et al., 2013). Analyses of

variance of root weight (g) measurement after 21 DAP reflected highly significant

differences among the 20 hybrids, all the three cold temperature treatments, and the

interaction (Table 2.2). According to the study of (Wijewardana et al., 2015), root dry

weight varied significantly among the corn hybrids.

Among the hybrids, Pioneer 1637 had the highest value of root weight and

showed (0.365 g), while DeKalb 62-08 had the lowest averages recorded and showed

(0.200 g) according to the results of the table (2.8). Temperature has been shown impact

on root initiation and growth. Therefore, here we also measure the root weight to uncover

temperature effects on overall roots development. Dry root weight was measured at 21

days of growth. There were highly significant differences among cold temperature

treatments, so 10°C had the highest value of root weight (0.331 g), while 7.2°C recorded

(0.217 g). In addition, there were significant interactions for this trait readings viewed in

the table (2.8). Hybrids DeKalb 62-08 at 10°C showed greater averages of dry root

weight (0.469 g).

The following figure (2.6) illustrates the influence of temperature treatments on

root weight (g) of twenty commercial corn hybrids after 21 DAP. Interestingly, hybrids

DKC 58-06, DKC 60-63 and DKC 62-08 which are susceptible to coldness did not show

great differences in root weight among the three cold temperature treatments after 21

days of growth. Unlike the above hybrids, DKC 42-37, DKC 47-35, DKC 49-29, DKC

38

50-84, DKC 53-78, and DKC 54-38 displayed great differences among each temperature

treatment with the same duration of growth.

Table 2.8 Effect of cold temperature treatments on root weight (g) after 21 days (RW 21) of 20 corn hybrids.



DeKalb 42-37 0.133 l 0.190 jk 0.375 cd 0.233 h

DeKalb 47-35 0.120 l 0.181 jk 0.347 de 0.216 ij

DeKalb 49-29 0.128 l 0.221 hi 0.406 c 0.252 f

DeKalb 50-84 0.159 k 0.244 gh 0.469 a 0.291 e

DeKalb 53-78 0.287 f 0.325 e 0.439 b 0.350 b

DeKalb 54-38 0.239 h 0.267 fg 0.417 c 0.308 d

DeKalb 55-20 0.228 hi 0.242 gh 0.299 ef 0.257 f

DeKalb 55-93 0.225 hi 0.241 gh 0.312 ef 0.259 f

DeKalb 58-06 0.206 ij 0.213 i 0.215 i 0.211 jk

DeKalb 60-63 0.214 i 0.231 h 0.234 h 0.226 hi

DeKalb 62-08 0.203 ij 0.197 j 0.202 ij 0.200 k

DeKalb 67-57 0.222 hi 0.247 gh 0.273 fg 0.248 fg

DeKalb 69-29 0.225 hi 0.253 g 0.299 ef 0.259 f

Pioneer 9329 0.184 jk 0.200 j 0.227 hi 0.204 jk

Pioneer 0339 0.300 ef 0.368 d 0.383 cd 0.350 b

Pioneer 0636 0.211 i 0.224 hi 0.221 g 0.230 h

Pioneer 0843 0.214 i 0.219 i 0.278 fg 0.237 gh

Pioneer 1197 0.290 f 0.323 e 0.339 de 0.317 cd

Pioneer 1637 0.291 ef 0.350 de 0.453 ab 0.365 a

Pioneer 2089 0.251 g 0.325 e 0.409 c 0.329 c

Average 0.217 c 0.253 b 0.331 a 0.267


39

Figure 2.6 Root weight (g) differs among corn hybrids under three cold temperature treatments after 21 DAP.

Field validation of seed emergence of corn hybrids planted in cool growing

conditions:

To study the effects of cold temperature on seed germination among different

corn hybrids in the field, field seed emergence test was conducted in the growing season

of 2016 at Mississippi State University. The germination rate was recorded after 14, 15,

and 16 days after planting with the same treatment to each corn hybrid. Results have

indicated that the ability to resist cold temperature among corn hybrids varies, and these

variations related to the lab experiments results. Statistical analysis has confirmed that the

germination rate among each hybrid, the germination rate for the same hybrid among

0

0.05

0.1

0.15

0.2

0.25

0.3

0.35

0.4

0.45

0.5

Roo

t Wei

ght (

g)

Hybrids

Root Weight (g) 21 Days

7.2°C 8.6°C 10°C

40

different days after planting, and the interaction between hybrids and dates were all

highly significant (Table 2.9).

Hybrid PHB 1637 is very susceptible to low temperature with (36.5 plant / row)

of germination rate, and it can be said that this is a late hybrid, whereas DKC 54-38 had

(70.6 plant / row) of field seed emergence (Table 2.10). Also, 16 days after planting

recorded highest number of seedling / row (69.7) compare with 14 DAP had only (52.9

plant / row). The interaction also varied significantly in field seed emergence, so (74.1

plant / row) were emerged after 16 DAP for hybrid DeKalb 60-63, while Pioneer 1637 ×

14 DAP had only (17.5 plant / row).

In general, according to the results of Figure (2.7), most Pioneer hybrids gave

lowest registered germination rate (number of seedlings) after 14 DAP compared with the

DeKalb hybrids, which recorded higher germination rate at the same time. There was a

large variation observed among the hybrids after 14, 15, and 16 DAP. Corn seed

germination is often affected by the temperature at early planting date leading to

disruption of seedling emergence and development. Laboratory and field cold

germination tests were performed on 20 commercial corn hybrids. Results of field

emergence were compared with the lab tests obtained from the same seed lots, and the

results were similar. Similar findings were reported by (Queijo, 2012) in cold tolerance

studies in maize.

41

Table 2.9 Analysis of variance across the hybrids and emergence rate treatments and their interaction for field seed emergence.

Source FSE

BLK **

HYB ***

DAP ***

HYB × DAP **

*, **, *** Significantly different at 0.05, 0.01 and 0.001 probability levels, respectively.

Figure 2.7 Seed emergence rate (number of seedlings / plot) for the field validation experiment of corn hybrids planted in cool growing conditions after 14, 15, and 16 DAP.

0

10

20

30

40

50

60

70

80

Num

ber o

f see

dlin

g / p

lot

Hybrids

Field Seed Emergence

14-DAP 15-DAP 16-DAP

42

Table 2.10 Effect of planting early on (FSE) field seed emergence (number of seedling / row) of 20 corn hybrids.

Hybrids Temperatures Average 14 DAP 15 DAP 16 DAP

DeKalb 42-37 59.4 e * 68.1 abc 70.8 ab 66.1 abc

DeKalb 47-35 59.3 e 67.5 abc 70.0 ab 65.6 abc

DeKalb 49-29 59.6 e 68.6 abc 71.3 a 66.5 abc

DeKalb 50-84 63.8 d 69.4 ab 70.9 ab 68.0 a

DeKalb 53-78 68.6 abc 69.9 ab 70.8 ab 69.8 a

DeKalb 54-38 66.6 c 72.1 a 73.1 a 70.6 a

DeKalb 55-20 64.5 cd 69.6 ab 70.8 ab 68.3 a

DeKalb 55-93 65.6 c 68.0 abc 70.0 ab 67.9 ab

DeKalb 58-06 64.8 cd 70.4 ab 72.5 a 69.2 a

DeKalb 60-63 63.9 d 72.4 a 74.1 a 70.1 a

DeKalb 62-08 43.4 h 64.9 cd 71.1 a 59.8 dc

DeKalb 67-57 22.6 k 52.6 fg 65.4 c 46.9 f

DeKalb 69-29 60.0 e 63.5 d 72.0 a 65.2 abc

Pioneer 9329 60.9 de 68.4 abc 71.0 a 66.8 abc

Pioneer 0339 42.3 hi 58.6 e 66.6 c 55.8 ed

Pioneer 0636 41.8 i 64.8 cd 72.0 a 59.5 dc

Pioneer 0843 29.0 j 54.4 f 65.9 c 49.8 ef

Pioneer 1197 43.4 h 65.5 c 72.6 a 60.5 bcd

Pioneer 1637 17.5 l 41.3 i 50.9 g 36.5 g

Pioneer 2089 61.1 de 70.9 ab 72.9 a 68.3 a

Average 52.9 c 65.1 b 69.7 a 62.6

Values are means of 4 replicates. Means separation within hybrid or emergence averages, and means within hybrid × emergence with the same letters are not significantly different at P > 0.01 using LSD. * Seed rate was near 35,000 plants per acre so that after emergence and stand counts plants were thinned to 65 plants per 30’ row in a given plot.

43

Conclusions:

The main idea of this study is to test the 20 commercial corn hybrids for the

ability to germinate under cold conditions. As a result, growers will select hybrids which

suitable for planting early and can be planted when soil temperatures are near 10°C

(Queijo, 2012). The reason for planting earlier is to avoid heat and drought during the

reproductive phases. The twenty commercial corn hybrids showed significant

variabilities in their responses to cold temperature for germination traits, radicle length,

root length, root weight and field seed emergence. The three temperature treatments

significantly affected corn germination and growth traits measured. Also, the interactions

between temperatures and hybrids were highly significant for most of the measured traits.

The hybrids (DKC 53-78, DKC 55-20, DKC 60-63, DKC 62-08, and DKC 67-57)

showed a significantly higher percentage of germination than most hybrids under 7.2°C

after 7 DAP. Based on this study combined, these hybrids can be used for early planting.

It can be said that the corn producers could select the hybrids for planting early in order

to optimize corn production in the field. The selected hybrids may perform better than

other hybrids planted early under cold growing conditions. In order to evaluate the

performance of the hybrids before recommending them to the producers, these results

have to be validated under field conditions to accomplish the maximum benefit of early

season seeding. Many more factors throughout the season contribute to yield, but uniform

germination and emergence is critically important.

44

Literature Cited:

AOSA. 2013. Rules for testing seeds. Association of Official Seed Analysts, Ithaca, NY.

Dezfuli, P. M., F. Sharif-Zadeh, and M. Janmohammadi. 2008. "Influence of priming techniques on seed germination behavior of maize inbred lines (Zea mays L.)." Journal Of Agricultural And Biological Science 3, no. 3:22-25.


Gardner, F.B., R.B. Pearce and R.L. Mitchell. 1984. Physiology of crop plants. 1st Edition, Published by Iowa State Pr (1984).

Heyne, E.G. and H. H. Laude. 1940. Resistant of corn seedlings to high temperature in laboratory tests. J.Am. Soc.Agron. 32:83 – 104.

Imran, M., Mahmood, A., Romheld, V., and Neumann, G. 2013. Nutrient seed priming improves seedling development of maize exposed to low root zone temperatures during early growth. Eur. J. Agron. 49:141–148.

International Rules for Seed Testing. 2008. International Seed Testing Association Chapter5: germination test. pp.1-57.

Queijo Marcelo, 2012. Cold Tolerance Studies in Maize. A dissertation Submitted to Michigan State University. pp.19.

SAS Institute. 2013. The SAS System for Windows. Release 6.1. SAS Inst., Cary, NC.

Sivakumar P.V. and P. Thamizhiniyan. 2012. Enhancement in growth and yield of tomato by using AM fungi and Azospirillum. International Journal of Environmental Biology. 2(3): 137-141.

Sozharajan, R. and S. Natarajan. 2013. "Germination and Seedling Growth of Zea mays L. Under Different Levels of Sodium Chloride Stress". International Letters of Natural Sciences. ISSN: 2300-9675.

Wijewardana, C., Hock, M., Henry, W. B., and Reddy, K.R. 2015. Screening corn hybrids for cold tolerance using morphological traits for early season seeding. Crop Sci. 19:75–78.

Yoshida, S., and S. Hasegawa. 1982. The rice root system: Its development and function In: Drought resistance in crops with emphasis on rice. Int. Rice Res. Inst., Manila, Philippines. pp.97–114.

45

CHAPTER III

CORN HYBRIDS SEED GERMINATION RESPONSES TO COLD TEMPERATURE

Abstract:

The aim of this study is to determine the effect of different levels of cold

temperature on germination characteristics of DKC 42-37, DKC 69-29, P 0339, and P

2089 hybrids (Zea maize L.). A laboratory study was conducted in controlled temperature

incubators in the Plant and Soil Sciences Department at Mississippi State University

2016. A factorial experiment arranged in completely randomized design with four

replications was used. Each temperature × hybrid treatment was replicated four times

with 50 seed per replicate at 3 levels of temperature: standard 10°C, low 8.6°C, and very

low 7.2°C. Standard germination assays confirmed all seed germinated at or near 100

percent under optimal conditions. Seeds were placed in plastic trays (25 × 35 cm) with

three layers of moistened seed germination paper. The samples were monitored daily to

ensure that the filter paper remained moist. The trays were examined at 2 hour intervals

following incubation. MSG, T50, SGR, and GVI increased significantly with increasing

temperature among all the corn hybrids. The present study investigated the corn hybrids

seed germination responses to cold temperature. The results of this study are expected to

be beneficial to the farmers elsewhere and the information obtained could be useful for

other corn hybrids. The objectives of this study are: 1. To quantify the effects of cold

46

temperature on seed germination rate. 2. To evaluate the effects of different cold

temperature on seed germination behavior of corn hybrids under laboratory conditions to

find out how fast they germinated. 3. Classify hybrids for response to cold temperature

using cumulative seed germination. There were no significant deferences among hybrids

for T50 %. The interactions between temperatures and hybrids were highly significant for

most of the measured traits. P0339 germinated faster. The results showed that standard

germination performance occurred at 10ºC for all hybrids, but these hybrids performed

well under other cold treatments. Therefore, the temperature had a major influence on

seed germination parameters. These findings are useful for selection of hybrids and

determination of soil temperature conditions for early planting.

Keywords:

Corn hybrids, Germination, Cold temperature test, Maximum germination,

Germination rate, Velocity index.

Abbreviations:

(MSG): Maximum seed germination. (T50): Time to 50 % Germination. (SGR):

Seed germination rate. (GVI): Germination velocity index.

Material and Methods:

The study was conducted in controlled temperature incubators in the laboratory of

the Plant and Soil Sciences Department at Mississippi State University. Seeds of four

corn hybrids from DeKalb and Pioneer Seed Companies were used for this study to

evaluate corn hybrids seed germination response to cold temperature. These hybrids

(DKC 42-37, DKC 69-29, P 0339, and P 2089) (Table 3.1) were selected depending on

the results of a prior, related experiment. One of these hybrids was full season and one

47

short season for each company. All seeds were new and kept in cold storage to maintain

seed quality prior to testing. Standard germination assays confirmed all seed germinated

at or near 100 percent under optimal conditions. Each temperature × hybrid treatment was

replicated four times with 50 seed per replicate (4 corn hybrids × 3 temperature levels)

standard 10°C, low 8.6°C, and very low 7.2°C. The experiment was then repeated. The

germination of corn seeds was performed according to the rules described by the

Association of Official Seed Analyst (AOSA, 2013). Seeds were placed in plastic trays

(25 × 35 cm) with three layers of seed germination paper moistened with distilled water,

two in the bottom and one on the top. The trays were then incubated in germination

chambers at the three constant levels cold temperatures. Replicates for each hybrid were

completely randomized within the germination chamber for each temperature in order to

minimize the potential of small temperature changes within the chambers. The samples

were monitored daily to ensure that the filter paper remained moist. The trays were

examined at 2 hour intervals following incubation. Germinated seeds were counted and

recorded over time. A seed was considered germinated with a radicle length of at least 2

mm (Dezfuli et al., 2008; and Dolapo and Modi, 2015) and were subsequently discarded.

Table 3.1 Four corn hybrids from DeKalb and Pioneer seed companies with hybrid name and relative maturity.

Brand Hybrid Relative Maturity

1 DeKalb 42-37 92

2 DeKalb 69-29 119

3 Pioneer 0339 103

4 Pioneer 2089 120

48

Measurements of germination characteristics:

SigmaPlot 11 (Systat Software, 2008) was used to estimate: -

• Maximum seed germination (MSG).

• Time to 50 % Germination (T50).

• Seed germination rate (SGR).

• Germination velocity index (GVI).

Maximum seed germination (MSG):

Maximum seed germination response to temperature was analyzed using

quadratic model functions Equation (3.1) for all hybrids (Kakani et al., 2002).

MSG = a + bx + cx2 (3.1)

where:

(x) is the temperature treatment, and (a) and (b) are hybrids-specific quadratic

equation constants generated using regression function in SigmaPlot 11.

Time to 50 % Germination (T50):

The time to 50 % germination was calculated according to the following formula

of Coolbear et al. (1984) modified by Farooq et al. (2005):

T50 = ti + {(𝑁/2) − 𝑛𝑖} (𝑡𝑖−𝑡𝑗)

𝑛𝑖−𝑛𝑗 (3.2)

where:

(N) is the final number of germination and (ni , nj) are cumulative number of

seeds germinated by adjacent counts at times (ti and tj ) when ni< N / 2 < nj.

49

Seed germination rate (SGR):

The germination rate was calculated according to ISTA method (3.3):

SGR = ∑ 𝑛𝑖/ 𝐷𝑖𝑗

𝑖=1 (3.3)

where:

(n) is the number of seeds emerged on (ith) day and (Di) is the number of days

counted from the beginning of the experiment. (j) is set to 10 days in this experiment.

Germination velocity index (GVI):

Germination velocity index (GVI) which measures the speed of seed germination

was calculated according to Maguire (1962) formulae (3.4):

GVI =𝐺1

𝑁1+

𝐺2

𝑁2+ ⋯

𝐺𝑛

𝑁𝑛 (3.4)

where:

G1, G2…Gn = number of germinated seeds in the first, second… last count.

N1, N2…Nn = number of days after sowing at the first, second… last count.

Statistical analysis:

The design of experiment was a completely randomized design laid out with a

factorial arrangement of treatments. Each hybrid × temperature treatment was replicated

four times. The seed parameters were analyzed using one-way ANOVA procedure

(PROC GLM, SAS 9.4) in SAS 9.4. (SAS Institute 2013, Cary, NC, USA), and the

hybrids and temperature considered as sources of variance. Data were presented to the

50

analysis of variance for maximum seed germination (MSG), time to 50 % Germination

(T50), seed germination rate (SGR), and germination velocity index (GVI) for each hybrid

using SigmaPlot 11. Treatments means were compared using least significant test (LSD)

at the (P > 0.01) level of probability. The cumulative seed germination time course data

were recorded at two hour intervals and fitted using Excel to generate estimates of MSG,

time to reach 50% germination (T50), and velocity seed germination (GVI).

The experiment was repeated twice, and there was a similarity between the two

experiments. The data were combined and analyzed appropriately.

Results and Discussion:

Maximum seed germination (MSG):

The analysis of variance revealed that there were significant differences (P ˃

0.01) among temperatures, hybrids, and their interactions for the MSG percentage trait

(Table 3.2).

Table (3.3) shows the effect of cold temperature treatments on maximum seed

germination (MSG) for the four commercial corn hybrids evaluated. The MSG

percentages varied significantly among the hybrids at the exception of the LSD (P >

0.01). Pioneer 2089 hybrid had the greatest average of MSG (93.7 %), while hybrid

DeKalb 42-37 had the lowest percentage (88.5 %). Temperatures also differed

significantly in this trait, and the percentages ranged from (88.9 %) at 7.2°C to (94.1 %)

at 10°C. Hybrids × temperatures potential interaction was also significant for MSG, so a

higher percentage (97.3 %) was observed for hybrid Pioneer 0339 at 10°C, while (84.5

%) was the lower MSG at 7.2°C.

51

Figure (3.1) shows the maximum seed germination percentage for four corn

hybrids under three deferent cold temperatures. The MSG increased linearly with

increasing of temperature for all hybrids, which may be due to the germination process

itself and extent hybrids response of temperature, seed deterioration, and dormancy loss

(Hsu et al., 1984 and Roberts, 1988). Several seed germination studies on different crops

observed that MSG is affected by temperature changes and genotypes (Bisoondat et al.,

2011). However, the present study provides the new concept of MSG to determine the

response these hybrids to cold treatment.

Table 3.2 Analysis of variance across the hybrids and temperature treatments and their interaction of maximum seed germination percentage (MSG %), time to 50 % Germination (T50), seed germination rate (SGR), and germination velocity index (GVI).

Source MSG % T50 SGR GVI

TEMP *** *** *** ***

HYB *** NS *** ***

TEMP × HYB * * *** **

*, **, *** Significantly different at 0.05, 0.01 and 0.001 probability levels, respectively. NS: non-significant at P > 0.05.

52

Table 3.3 Effect of cold temperature treatments on maximum seed germination (MSG), time to 50 % germination (T50), seed germination rate (SGR), and germination velocity index (GVI) of four corn hybrids.

Traits Hybrids Temps.

DeKalb 42-37

DeKalb 69-29

Pioneer 0339

Pioneer 2089 Average

MSG % 7.2°C 84.5 e

88.4 de

91.1 bcd

91.6 bcd

88.9 b

8.6°C 89.2 cd

91.9 bcd

92.8 bc

94.0 ab

92.0 a

10°C 91.8 bcd

92.6 bc

97.3 a

94.7 ab

94.1 a

Average 88.5 c

91.0 b

93.7 a

93.4 a

91.4

T50 7.2°C 12.27 a

12.29 a

12.30 a

12.32 a

12.28 a

8.6°C 11.32 a

11.35 a

11.31 a

11.33 a

11.33 b

10°C 7.68 b

7.53 b

7.71 b

7.65 b

7.66 c

Average 10.42 a

10.39 a

10.44 a

10.43 a

10.42

SGR 7.2°C 0.082 f

0.081 f

0.082 f

0.081 f

0.082 c

8.6°C 0.089 e

0.088 e

0.089 e

0.088 e

0.088 b

10°C 0.118 d

0.137 c

0.157 b

0.177 a

0.147 a

Average 0.096 d

0.102 c

0.109 b

0.115 a

0.106

GVI 7.2°C 18.9 h

20.3 fgh

21.7 ef

19.8 gh

20.2 c

8.6°C 21.0 fg

20.7 fgh

23.3 de

23.9 d

22.2 b

10°C 36.0 bc

35.4 c

38.4 a

37.6 ab

36.8 a

Average 25.3 b

25.4 b

27.8 a

27.1 a

26.4

Values are mean of 4 replicates. Means with the same letters are not significantly different at P > 0.01 level of significance according to LSD.

53

Figure 3.1 Influence of cold temperature on maximum seed germination (MSG) of four corn hybrids (DeKalb 42-37, DeKalb 69-29, Pioneer 0339, and Pioneer 2089). The points are recorded MSG % and fitted lines among them.

Germination time course is best describing and illustrating of the corn seed

germination and time series data for all the hybrids studied (Figure 3.2). Germination

time response differed among the four hybrids. Most corn hybrids were germinated at or

after 11 days under 7.2°C and 8.6°C, however, seed germination in most of the hybrids

began on or before the seventh day from incubation at 10°C. Time series analysis showed

a rapid rise in (MSG) of each hybrid with increasing temperature. Differences in MSG

response slopes among the hybrids indicated that may be attributed to seed dormancy,

although seeds were stratified as per AOSA recommendations. Differences in MSG

response slopes among the hybrids indicated that might be attributed to seed

84.00

86.00

88.00

90.00

92.00

94.00

96.00

98.00

7.2°C 8.6°C 10°C

Max

imum

seed

ger

min

atio

n %

Temperature, C°

Maximum seed germination (MSG)

DKC 42-37 DKC 69-29 P 0339 P 2089

54

Figure 3.2 Germination time course of four corn hybrids (DeKalb 42-37, DeKalb 69-29, Pioneer 0339, and Pioneer 2089) response to three levels of cold temperatures treatment (standard 10°C, low 8.6°C, and very low 7.2°C).

0102030405060708090

100

7 7.5 8 8.5 9 9.5 10 10.5 11 11.5 12 12.5 13 13.5 14 14.5 15 15.5Cum

ulat

ive

seed

ger

min

atio

n (%

)

7.2°C

0102030405060708090

100

7 7.5 8 8.5 9 9.5 10 10.5 11 11.5 12 12.5 13 13.5 14 14.5 15 15.5Cum

ulat

ive

seed

ger

min

atio

n (%

) 8.6°C

0102030405060708090

100

7 7.5 8 8.5 9 9.5 10 10.5 11 11.5 12 12.5 13 13.5 14 14.5 15 15.5Cum

ulat

ive

seed

ger

min

atio

n (%

)

Days

10°C

DKC 42-37 DKC 69-29 P 0339 P 2089

55

dormancy, although seeds were stratified as per AOSA recommendations. These results

are supported by the findings of (Seepaul et al., 2012).

Time to 50 % Germination (T50):

According to the analysis of variance in table (3.2), significant variation for cold

temperature treatments occurred in the trait of time to 50 % emergence. Although there

were no significant differences among the hybrids studied, there was a significant

interaction between the temperature and hybrids. Results indicate that the temperature

treatment effect was more important than the hybrids effect in determining of the time to

50 % germination response.

Highly significant differences among temperature effects were observed in table

(3.3) for the average time to 50% germination. In this experiment, 10°C had the fastest

times to reach to 50% germination as expected, while 7.2°C had the slowest time (7.66

and 12.28 days) respectively. No significant differences among hybrids were observed in

this trait with the expectation of the LSD (P > 0.01), and the time to 50 % germination

ranged from (10.39 to 10.44 days). A significant interaction was observed between

temperatures and hybrids in the T50 % germination. The hybrid DeKalb 69-29 at standard

temperature took less time (7.53 days) to reach to 50 % germination, whereas Pioneer

2089 at very low temperature took (12.32 days).

Figure (3.3) shows the effect of cold temperature test on time to 50 %

germination. The results showed that there were differences among the temperature

levels, as the time to reach 50% germination was longest under very cold temperatures,

and gradually decreased at cold, and it was shorter under standard (Figure 3.2). The

hybrids followed the same behavior in (T50) germination under the effect of cold

56

temperature treatments. Although there were no significant deferences among hybrids,

they varied at standard temperature.

Figure 3.3 Influence of cold temperature on time to 50 % germination / days (T50) of four corn hybrids (DeKalb 42-37, DeKalb 69-29, Pioneer 0339, and Pioneer 2089). The points are recorded T50 and fitted lines among them.

Seed germination rate (SGR):

Analyses of variance of seed germination rate (SGR) measurement reflected

highly significant differences among the three cold temperature treatments, among

hybrids, and the interaction (Table 3.2).

The SGR varied highly significantly among temperatures, the highest value was

recorded (0.147) d−1 at 10°C, while the lowest (0.082) was observed at (7.2°C) (Table

5.00

6.00

7.00

8.00

9.00

10.00

11.00

12.00

13.00

7.2°C 8.6°C 10°C

Tim

e to

50

% g

erm

inat

ion,

d

Temperature, C°

Time to 50 % germination, days

DKC 42-37 DKC 69-29 P 0339 P 2089

57

3.3). Highly significant differences were observed among hybrids (P ˃ 0.01) for SGR,

and the hybrid Pioneer 2089 had higher SGR (0.115), while DeKalb 42-37 showed lower

SGR (0.096) d−1. The interactions were also highly significant in seed germination rate.

The values ranged from (0.081) to (0.177) d−1. The interaction between hybrid Pioneer

2089 with 10°C had higher SGR, while DeKalb 69-29 and Pioneer 2089 at 7.2°C

showed lower value of SGR. These results in germination are supported by the findings

of (Hene and Laude, 1940; Hsu et al., 1984; and Roberts, 1988).

For clarity, predictor lines of four hybrids and three cold temperature treatments

are presented in (Figure 3.4). It can be said that the seed germination rate of hybrids

varied greatly depending on temperature. This is due to higher rates of the relationship

between seed germination rate and the time to reach to 50 % germination. SGR

calculated as the reciprocal of T50, whenever decreased, SGR increased linearly with

increasing temperatures.

58

Figure 3.4 Influence of cold temperature on seed germination rate / days (SGR) of four corn hybrids (DeKalb 42-37, DeKalb 69-29, Pioneer 0339, and Pioneer 2089). The points are recorded SGR and fitted lines among them.

Germination velocity index (GVI):

Germination velocity index (GVI) is an expression of speed and totality of

germination, and their interaction. The value of GVI expresses the maximum cumulative

germination percentage divided by the number of days according to the explanation of

Brown & Mayer (1988). The analysis of variance indicates that significant differences

were observed for the germination velocity index among temperatures, among hybrids,

and their interaction (Table 3.2).

In this study, there were highly significant differences among temperatures for

germination velocity index (Table 3.3). Results have shown that at 7.2°C, the lowest

0.060

0.080

0.100

0.120

0.140

0.160

0.180

7.2°C 8.6°C 10°C

Seed

ger

min

atio

n ra

te (d

ays

- 1)

Temperature, C°

Seed germination rate (SGR)

DKC 42-37 DKC 69-29 P 0339 P 2089

59

value of GVI was recorded (20.2), while at 10°C was the highest (36.8). Also, there were

highly significant differences for this trait among corn hybrids, Pioneer 0339 showed the

highest value for GVI (27.8), while DeKalb 42-37 recorded showed the lowest value

(25.3). Significant interactions were observed for the relative of the three levels of

temperature by hybrid. Overall the hybrid Pioneer 0339 at 10°C treatment caused a major

mean of the GVI (38.4), and DeKalb 42-37 at 7.2°C had a lowest mean (18.9).

Figure (3.5) shows the effect of cold temperature on germination velocity index.

This figure illustrates that the speed of germination was faster in all hybrids at standard

temperature than at very cold temperature which was expected. Germination time course

also illustrates the speed of germination (Figure 3.2). This suggested that cold

temperature influences the speed of germination for corn hybrids. At 7.2°C hybrids seeds

began 12 days after incubation and spent more than 3 days to reach to (MSG), at 8.6°C

they started at 11 days and needed less than 3 days to reach to (MSG). While at 10°C

hybrids began about 7 days after incubation and spent less than 2 days to reach to (MSG).

Our data support other studies reported that germination was significantly slower at low

temperatures than when the temperature was high and constant (Bosci and Kovacs, 1990;

Birch et al., 2003; Idikut, 2013). This study relies more on the germination velocity index

than germination rate as an indicator of germination speed. Mabhaudhi and Modi (2010)

observed that germination velocity index is a better indicator of germination speed than

germination rate.

60

Figure 3.5 Influence of cold temperature on germination velocity index (GVI) of four corn hybrids (DeKalb 42-37, DeKalb 69-29, Pioneer 0339, and Pioneer 2089). The points are recorded GVI and fitted lines among them.

Conclusions:

The current study quantified the effects of cold temperature on maximum seed

germination, time to 50 % germination, seed germination rate, and seed germination

velocity of four corn hybrids. The findings of the present study showed that temperature

affects the germination performance of corn hybrids differentially across hybrids. MSG,

T50, SGR, and GVI were increased significantly with increasing temperature among all

the corn hybrids. There were no significant deferences among hybrids for T50 %. The

interactions between temperatures and hybrids were highly significant for most of the

measured traits. The speed of germination is important for uniform seedling

establishment depending on the temperature conditions. Of the 4 corn hybrids studied,

18

23

28

33

38

7.2°C 8.6°C 10°C

Ger

min

atio

n ve

loci

ty in

dex

Temperature, C°

Germination velocity index (GVI)

DKC 42-37 DKC 69-29 P 0339 P 2089

61

P0339 was classified as a faster germinator. There were no significant differences

between early hybrids 93 to 105 RM (Relative Maturity) and full season 115 to 120 RM

in germination % and rate in both experiments, suggesting hybrid genetics played a larger

role than relative maturity (early or late). It would be good for producers to know and that

they should pay attention to the cold vigor ratings provided by the seed companies.

Although the study was laboratory-based, the findings demonstrated that standard

germination occurred at 10ºC for all hybrids, but these hybrids performed relatively well

under increasingly colder treatments. Recommended soil temperatures for planting at

approximately 10°C agrees with our data. The cumulative temperature response index

method used in the current study identified the hybrids and demonstrated that only slight

variability existed among them. It is less obvious when a single factor is observed, so the

effect is better understood in the context of interaction between temperatures and corn

hybrids. Further studies are required on the performance of the corn hybrid seeds at

different levels of temperatures regimes under a wide range of field conditions.

62

Literature Cited:

AOSA. 2013. Rules for testing seeds. Association of Official Seed Analysts, Ithaca, NY.

Birch, C.J., Vosb, J. and van der Puttenb, P.E.L. 2003. Plant development and leaf area production in contrasting cultivars of maize grown in a cool temperate environment in the field. Eur. J. Agron. 19:173-188.

Bisoondat, M., K. R. Reddy, S. Ramdeo, and B. Baldwin. 2011. Switchgrass (Panicum virgatum L.) Intraspecific Variation and Thermotolerance Classification Using In Vitro Seed Germination Assay. American Journal of Plant Sciences, Vol 02, Iss 02, pp 134-147.

Bosci, J. and Kovacs, G. 1990. Inheritance of the rate of germination and emergence at low temperatures in maize. Acta Agronomica Hungarica 39:127-135.

Brown R. F. and D. G. Mayer, 1988. Representing Cumulative Germination: The Use of the Weibull Function and Other Empirically Derived Curves. Annals of Botany, Vol 61, Iss 2, pp. 127–138.

Dezfuli, P. M., F. Sharif-Zadeh, and M. Janmohammadi. 2008. "Influence of priming techniques on seed germination behavior of maize inbred lines (Zea mays L.)." Journal Of Agricultural And Biological Science 3, no. 3: 22-25.


Farooq M., S.M.A. Basra, K. Hafeez, and N. Ahmad. 2005. Thermal hardening: a new seed vigor enhancement tool in rice. Acta Botanica Sinica. 47:187-193.

Heyne, E.G. and H. H. Laude. 1940. Resistant of corn seedlings to high temperature in laboratory tests. J.Ame. Soc.Agron. 32:83-104.

Hsu F. H., C. J. Nelson and W. S. Chow. 1984. “A Mathematical Model to Utilize the Logistic Function in Germination and Seedling Growth,” Journal of Experimental Botany, Vol. 35, No. 11, pp. 1629-1640.

Idikut, L. 2013. The Effects of light, temperature and salinity on seed germination of three maize forms. Greener J. Agric. Sci. 3 246-253.

Kakani V. G., P. V. Prasad, P. Q. Craufurd and T. R. Wheeler. 2002. “Response of in vitro Pollen Germi-nation and Pollen Tube Growth of Groundnut (Arachis hypogaea L.) Genotypes to Temperature,” Plant Cell and Environment, Vol. 25, No. 12, pp. 1651-1661.

63

Mabhaudhi, T. and Modi, A.T. 2010. Early establishment performance of local and hybrid maize under two water stress regimes. S. Afr. J. Plant Soil 27: 299-304.

Maguire, J.D. 1962. Speed of germination-aid in selection and evaluation for seedling emergence and vigour. Crop Sci. 2: 176 -177.

Roberts E. H. 1988. “Temperature and Seed Germination,” In: S. P. Long and F. I. Woodword, Eds., Plants and Tem-perature, Symposia of the Society for Experimental Biol-ogy, Cambridge, pp. 109-132.

SAS Institute. 2013. The SAS System for Windows. Release 6.1. SAS Inst., Cary, NC.

Seepaul, R., B. Macoon, and K.R. Reddy, 2012. Ecotypic differences in switchgrass seed germination responses to in vitro osmotic stress. Seed Technol. 34:173–182.

Systat Software. 2008. SigmaPlot for Windows. Version 11.0. Systat Software, Point Richmond, CA, USA.

64

CHAPTER IV

DISSERTATION CONCLUSIONS

Early season corn planting is one of the best strategies to stabilize corn yield by

avoiding high temperatures during the critical grain filling period throughout the US corn

production region. Planting early with uniform seed germination and stand establishment

would help to attain high synchronization of the reproductive stages and to reach maturity

before the occurrence of harsh conditions. If producers adopt early planting, cold

temperatures may negatively affect corn yield. It is important to select hybrids that are

suited for planting earlier in the southern United States. Experiments were conducted by

imposing low temperatures during seed germination. Twenty commercially available

corn hybrids were evaluated for seed germination and root elongation to determine if

some hybrids germinate better at cooler temperatures than others and to determine

variation in root elongation at cold temperatures among commercially available hybrids.

The second experiment quantified the effects of cold temperature on maximum seed

germination, time to 50 % germination, seed germination rate, and seed germination

velocity of four corn hybrids. The twenty commercial corn hybrids showed significant

variabilities in their responses to cold temperature for germination traits, radicle length,

root length, root weight and field seed emergence. The three temperature treatments

significantly affected corn germination and growth traits measured. Also, the interactions

65

between temperatures and hybrids were highly significant for most of the measured traits.

Furthermore, MSG, T50, SGR, and GVI increased significantly with increasing

temperature among all the corn hybrids. There were no significant differences among

hybrids for T50 %. Of the 4 corn hybrids studied in the second experiment, P0339 was

classified as a faster germinator. There were no significant differences between early

hybrids 93 to 105 RM (Relative Maturity) and full season 115 to 120 RM in germination

% and rate in both experiments, suggesting hybrid genetics played a larger role than

relative maturity (early or late). Based on this study combined, these hybrids can be used

for early planting. Corn producers could select the hybrids for planting early in order to

optimize corn production in the field. The selected hybrids may perform better than other

hybrids planted early under cold growing conditions. The findings of the present study

showed that temperature affects the germination performance of corn hybrids

differentially across hybrids. Although the study was laboratory-based, the findings

demonstrated that standard germination occurred at 10ºC for all hybrids, but these

hybrids performed relatively well under increasingly colder treatments. Recommended

soil temperatures for planting at approximately 10°C agrees with our data. The

cumulative temperature response index method used in the current study identified the

hybrids and demonstrated that only slight variability existed among them. It would be

good for producers to know and that they should pay attention to the cold vigor ratings

provided by the seed companies. Further studies are required on the performance of the

corn hybrid seeds at different levels of temperatures regimes under a wide range of field

conditions. In order to evaluate the performance of the hybrids before recommending

66

them to the producers, these results have to be validated under field conditions to

accomplish the maximum benefit of early season seeding.

temperature effect on maize germination and root elongation

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