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Ghosh, Shahed, and Robin: Polyethylene Glycol Induced Osmotic Stress Affects Germination and Seedling Establishment of Wheat Genotypes

Abstract

Wheat is globally an important cereal crop. Environmental stress, especially drought stress can play an important role in the reduction of plant growth, specifically during germination in arid and semi-arid regions. Polyethylene glycol (PEG) treated hydroponic conditions create negative osmotic potential which is compared with moisture deficit stress. The main objective of this study was to investigate the effects of PEG 6000 induced moderate osmotic stress on germination indices of 22 wheat varieties. In order to study the effects of osmotic stress on germination indices in wheat cultivars, an experiment was conducted, using a completely randomized design with three replications under two different levels of PEG-6000: 0% and 10%. PEG stress significantly reduced percent germination, shoot length and root length. PEG stress significantly increased root-shoot ratio and oven dry weight. Principal component analysis revealed response of traits of tolerant wheat varieties under osmotic stress. Correlation study revealed the significant relationships among germination indices. The variety BARI Gom-30 recorded comparatively higher root length (6 cm), shoot length (7.8 cm), root-shoot ratio (1.37) followed by the variety Sonalika whereas the variety Kalaysona recorded the lowest root length (2.7 cm) and shoot length (2.8 cm) under PEG stress. Evolved information of this research including selected traits such as germination percentage, root-shoot ratio and dry weight of seedlings could be exploited in wheat breeding program for drought and osmotic stress tolerance.

INTRODUCTION

Wheat (Triticum aestivum L.) is a staple food for over 35% of the world’s population, and is also the first grain production in most developing countries (Metwali et al. 2011). Bread wheat is the main food in many countries and about 70 percent of human calories and 80 percent of human protein comes from its intake (Ghanifathi et al. 2011). Abiotic stress, especially drought stress, is a global problem that significantly hampers global crop production (Pan et al. 2002). It is one of the major causes of crop failure worldwide, generally lowering average crop yield by more than 50 percent for many crop plants (Wang et al. 2003; Bayoumi et al. 2008). Water, the most important component of life, for humans and their crops is becoming an increasingly scarce commodity. Water scarcity inhibits plant growth and crop production more than any other single environmental factor in arid regions (Boyer 1982). In addition to other factors, arid and semi-arid climates can induce water stress during crop growth and development, resulting in reduced crop yield (Ashraf and Yasmin 1995). Despite this, water stress is recognized as a significant factor influencing the growth and yield of wheat (Ashraf and Naqvi 1995; Ashraf 1998). Differences between cultivars have been observed in response to constraints on soil moisture (Rascio et al. 1992; Iqbal et al. 1999). Water is important for plant growth at every stage, from seed germination to plant maturation. Water stress decreases crop yield irrespective of the stage of growth at which the adverse effect of water stress on crop yield may be more pronounced depending on the nature of crop species and even genotypes within the plant at some specific stage of growth (El-Far and Allan 1995). Substantial crop growth and yield to cope with drought stress, breeding for drought resistance can best be accomplished by choosing grain yield under field conditions (Richards 1978). It responds very differently to stress depending on the stage of growth at which a plant faces drought stress (Galies and Ho 1983). Plants may be affected by drought at any life stage, but certain phases are crucial such as those involving germination and seedling development (Pessarakli 1999). Seed germination is a major problem of wheat production. Many environmental factors affect it but the quality of soil moisture has a major effect on germination and eventual emergence. In addition to the reduction in total germination, the comparatively low supply of soil moisture results in delayed flowering, a condition of particular importance for vigor and eventual yield potential of many crops (Azam and Allen 1976). Germination levels and growth of seedlings have been reported to decline at low soil moisture levels. The rate of decline was found to be evident, varying with crop species and cultivars (Ashraf and Abu-Shakra 1978). Germination is a critical stage of plant life and the resistance to drought during germination makes a plant stable. In most of the developing countries, wheat is mainly grown without additional irrigation on rainfed lands. Crop germination and growth characteristics of seedling are very important factors in determining yield (Rauf et al. 2007). Dhanda et al. (2004) suggested that the index of seed vigor and shoot length are among the most prone to drought stress, accompanied by root length and length of coleoptiles. With the increase of osmotic stress levels (Heikal et al. 1981), the rate of seed germination and the final germination percentage as well as the amount of water consumed by the seeds were significantly decreased. Osmotic adjustment is the method of managing osmotic stress. Accumulation of solutes occurs under water deficiency which results in a reduction of the cell’s osmotic potential, which pulls water molecules into the cell to help maintain turgor. Turgor maintenance plays an important role in plant drought tolerance which may be due to its involvement in stomatal control and therefore photosynthesis (Ludlow et al. 1985). Polyethylene glycol (PEG) is used to artificially cause osmotic tension (Rauf et al. 2007; Khakwani et al. 2011). Polyethylene glycol (PEG) molecules are non-ionic, inert, and have impermeable chains that cause no physiological damage to water stress and retain the same water potential throughout the trial (Lu and Neumann 1998). PEG, a chemical that creates physiological drought, is commonly used under laboratory conditions to screen out drought resistant varieties at the early stage of seedlings. Previous studies have revealed that PEG can be used to alter the osmotic capacity of the culture of nutrient solutions and thus induce a fairly regulated deficit of plant water (Lagerwerff et al. 1961; Money 1989; Zhu et al. 1997).
The objective of this study was to compare the response of wheat genotypes under osmotic stress during germination and seedling growth. Results of this study will provide a theoretical basis of improving abiotic stress tolerance abilities of wheat seedling of dryland farming in the semiarid regions.

MATERIALS AND METHODS

Planting material and source

The experiment was conducted in a plant culture room under controlled condition. Twenty two wheat varieties were screened under two treatments: control and 10% PEG. Seeds of twenty two wheat varieties were collected from Bangladesh Agricultural Research Institute (BARI), Gazipur-1700 based on distinctive entity (Table 1). Clean tissue paper was used for moisture absorption and to provide mechanical support for emerging wheat seedlings.

Germination of seeds

Seeds were germinated on a petri dish. Three petri dishes were used for each genotype under each treatment and each petri dish was covered with tissue paper. The tissue papers were wetted by spraying water under controlled conditions. PEG 6000 was prepared by dissolving the required amount of PEG in distilled water. The tissue papers were wetted by spraying PEG under the treated condition. These wet tissue papers were used for germination of the seeds. Ten seeds were spread on each petri dish. Periodically a water splash in control and PEG solution in treated petri dishes were provided on the seeds. It took 1-2 days to germinate the seeds. After one week, seeds were grown into healthy dark green seedling with proper rooting and shooting. When the leaves were turning light green in color, it indicated that the inert food materials inside the seeds are exhausted.

Collection of data

Germination percentage, shoot length, root length, root/shoot ratio and oven dry weight were determined by using the following formula (Li 2008):
(1) Percent germination (PG) = n/N × 100, where n is the number of germinated seed at the seventh day; N is the number of total seeds.
(2) Shoot length (cm): Shoot length was measured from the root base to the tip of the shoot. This was measured on 7 days after sowing (Fig. 1).
(3) Root length (cm): Root length was measured from the root base to the tip of the root. This was measured on 7 days after sowing (Fig. 1).
(4) Root/shoot ratio: Ratio of root length over shoot length.
(5) Oven dry weight: Ten seedlings of each genotype under two treatments (control and 10% PEG) from three replications were randomly taken 7 days after sowing (DAS) for recording dry mass of seedling. Samples from each genotype were paper bagged individually and oven-dried at 60℃ for 72 hours or more until a constant dry weight is obtained.

Experimental design and data analysis

The experiment was conducted following a completely randomized design (CRD) with three replications and collected data were subjected to analysis of variance (ANOVA) by MINITAB® 17 software (Minitab Inc., State College, PA, USA). The treatment means were compared and grouped using Tukey’s pairwise comparison at the 0.05 level of significance. Principal Component Analysis (PCA) of selected traits was carried out to investigate association between traits and tolerance of varieties under treatment. The principal component (PC) scores were stored and ANOVA of the PC scores was performed using an one way ANOVA to explore the statistical significnce in treatment × variety interactions. A Pearson correlation analysis was carried out to explore relationship among the traits.

RESULTS

Effects on percent germination

PEG treatment markedly affected both germination and seedling growth (Fig. 1). Analysis of variance indicated that percent germination was highly significant for both treatment (P = 0.004) and variety (P < 0.001) but non-significant for treatment × variety interaction (P = 0.271) (Table 2, Fig. 2). Percent (%) germination was the highest under control (97%) and the lowest in 10% PEG treatment (94.2%). Among the varieties, V2, V10, V12, V15 and V18 (100%) had the highest percent germination and the variety V8 (81.6%) recorded the lowest germination.

Effects on shoot length

Shoot length was highly significant for both treatment and variety (P < 0.001) and significant for treatment × variety interaction (P = 0.005) (Table 2). Plants under control had the highest shoot length (9.3 cm) and those under 10% PEG treatment recorded the lowest shoot length (1.6 cm) (Fig. 3). Among the varieties, the variety V19 (7.8 cm) had the highest shoot length and the variety V7 (2.8 cm) had the lowest shoot length. Under treatment × variety interaction, the variety V1 recorded as the highest shoot length (9.3 cm) under control whereas the variety V22 recorded as the lowest shoot length (2.0 cm) under 10% PEG treatment (Table 3, Fig. 3).

Effects on root length

Root length (cm) was highly significant for both treatment (P = 0.004) and variety (P < 0.001) but non-significant for treatment × variety interaction (P = 0.215) (Table 2). Plant under control had the highest root length (4.3 cm) and those under 10% PEG treatment recorded the lowest root length (3.4 cm) (Fig. 4). Among the varieties, the variety V19 (6.0 cm) had the highest root length and the variety V7 had the lowest root length (2.7 cm). Among treatment × variety interaction, the variety V19 (7.6 cm) recorded as the highest root length under control whereas the variety V7 (2.4 cm) under control recorded the lowest root length (Table 3, Fig. 4).

Effects on root-shoot (R/S) ratio

Root-shoot ratio was highly significant for treatment (P < 0.001) and but non-significant for variety, treatment × variety interaction (Table 2). Plants under PEG treatment had the highest root shoot ratio (2.3) and the lowest root-shoot ratio (0.5) under control (Fig. 5). Under treatment × variety interaction, the variety V8 recorded the highest root-shoot ratio (9.3) under PEG treatment whereas the variety V2 recorded as the lowest root-shoot ratio under control (Table 3, Fig. 5).

Effects on PEG exposure on dry weight

Oven dry weight (g) was highly significant for both treatment and variety (P < 0.001) and non-significant for treatment × variety interaction (Table 2). Oven dry weight was increased under 10% PEG treatment (0.03 g) over control. The variety V8 had the highest oven dry weight (0.04 g) and the variety V1 has the lowest oven dry weight (0.02 g) (Fig. 6). Among the treatment × variety interaction, the variety V8 (0.04 g) recorded the highest oven dry weight whereas the variety V7 (0.01 g) recorded the lowest oven dry weight (Fig. 6). Within the variety, significant difference was found only in the variety V20 between control and 10% PEG treatment (Table 3, Fig. 6).

Principal Component Analysis

The most apposite combination of the studied traits was obtained from the principal component analysis where the vector length on biplot exhibited the magnitude of variation explained by respective trait and treatment × variety combinations in the PCA. PC1 and PC2 showed significant differences for treatment (P < 0.001) and genotype (P < 0.001) (Table 4). PC3 and PC4 showed significant differences for genotype (P < 0.001) (Table 5). PC1, PC2, PC3 and PC4 explained 51.4%, 20.5%, 16.9%, and 9.4% data variation respectively (Table 5). The first two principal components (PC) explained about 72% of the total data variation that showed the effect of PEG stress on seedling traits of wheat varieties. PC1 separated wheat genotypes for treatment effect and genotypic effect for positive coefficients of shoot and root length and negative coefficients of root-shoot ratio and dry weight (Fig. 7). PC2 separated genotypes for higher negative coefficients of percent germination, root length and dry weight (Fig. 7).

Correlation analysis

A Pearson correlation analysis showed significant relation among the observed traits (Table 5). Percent germination had significant positive correlation with shoot length and root length and negative correlation with root-shoot ratio. Shoot length had significant positive correlation with root length and negative correlation with root-shoot ratio and dry weight. Root length was significant but negatively correlated with root-shoot ratio whereas the root-shoot ratio had positive correlation with dry weight (Table 5).

DISCUSSION

Percent germination (PG)

Seed germination process is a crucial stage for seedling establishment under any stress environment. In this study, germination percentage of wheat genotypes was significantly affected by PEG-induced osmotic stress (Fig. 2). Previous studies reported that PEG induced osmotic stress delays the initiation of germination leading to reduction in germination percentage (Dhanda et al. 2004; Jajarmi 2009; Khakwani et al. 2011; Raza et al. 2012).

Shoot length (SL)

Shoot length of wheat genotypes was significantly affected by PEG-induced osmotic stress (Fig. 3). PEG stress induces artificial water deficit which decreases turgor pressure and reduces cell division resulting poor shoot growth (Lagerwerff et al. 1961). Previous studies observed significant decreases in shoot length of wheat varieties at the seedling stage under PEG stress (Rauf et al. 2007; Khakwani et al. 2011; Almaghrabi 2012).

Root length (RL)

Similar to shoot growth, root length was significantly reduced up to 82.9% under PEG-induced osmotic stress (Table 2). Induction of osmotic stress affects the water uptake and reduces turgor pressure that eventually causes reduction of root length. This result was in agreement with the findings of Jajarmi (2009) and Khakwani et al. (2011) who reported significant reduction of root length of wheat varieties under PEG-induced osmotic stress compared to the control.

Root shoot (R/S) ratio

The measured root-shoot ratio reflects comparative root and shoot growth patterns of a crop plant. A high root-shoot ratio means higher root growth while a lower root-shoot ratio means comparatively higher shoot growth. An increase in root-shoot ratio under PEG-induced osmotic stress indicated that PEG induced osmotic stress positively influenced root growth compared to shoot growth (Fig. 5). The increasing trend of root growth under osmotic stress might act as a survival mechanism of wheat plants (Robin et al. 2016; Hannan et al. 2020). These results were similar to the findings of Khakwani et al. (2011) and Rauf et al. (2007).

Seedling dry weight (g)

Significant variation was found in all 22 wheat varieties under PEG stress (P < 0.001, P < 0.004). Seedling dry weight increased by 50% under PEG over control (Fig. 6). Our results suggested that this seedling parameter is one the most important criterion for screening genotypes for drought tolerance at early growth stages. The present study clearly showed that PEG induced osmotic stress had greater inhibitory effects on seedling growth than on germination, and there was substantial genotypic variation in osmotic stress tolerance among the wheat varieties. The significant increment in seedling growth by PEG stress may be attributed to achievement of sufficient water and balanced nutrient uptake by growing more roots and its length. The deleterious effects of PEG may result in a significant decrease in photosynthesis and increase in respiration rate leading to a shortage of assimilates to the developing organs, thus slowing down growth or stopping it entirely. As PEG enhances osmotic pressure leading to reduction in water absorbance, cell division and differentiation are inhibited, which adversely affects metabolic and physiological processes (Khakwani et al. 2011). This causes more delay in initiation of germination followed by prolonged seed germination duration (Khakwani et al. 2011).

Trait Associations

Principal component analysis (PCA) indicated that contrasting variations were present in the varieties due to differences in germination and seedling growth of wheat genotypes (Fig. 7). PC1 had strong and positive coefficient for shoot length, root length and percent germination while showing strong and negative coefficient for root shoot-ratio and dry weight. PC2 had strong and negative coefficient for percent germination, root length, root-shoot ratio and dry weight. PC1 separated the varieties V2, V19, V20, V15 and V9 for shoot length, root length, percent germination under the control condition from other varieties over PEG treated condition (Fig. 7). Correlation studies show the nature and extent of association between any two pairs of parameters. Percent germination showed significant correlation with other parameters but shoot length showed significant and positive root length, and significant and negative correlation with root-shoot ratio and dry weight. This indicated that root and shoot growth are dynamic. Our results indicated that the underground part of the plant plays an important role under drought stress conditions (Siddique et al. 1990). Traits like percent germination, shoot length, root-shoot ratio of these varieties can be incorporated into other high yielding varieties to get maximum number of populations under osmotic stress. Thus, germination percentage, root-shoot ratio and dry weight of seedlings are the vital traits for screening cereal genotypes under osmotic stress during germination and seedling establishment (Fig. 7).
In conclusions, Wheat is one of the globally important main cereal crops. Many abiotic stresses especially drought stress is considered as a serious threat to wheat production. Drought stress induces osmotic stress which commonly reduces average yield for many crop plants by more than 50%. PEG induces osmotic stress which inhibit plants to uptake available water surrounding the root zone. Among the 22 wheat varieties, BARI Gom-30 was found better followed by the variety Sonalika compared to other wheat varieties in germination and seedling growth abilities under osmotic stress. Our results aid in future screening of wheat varieties at both vegetative and reproductive stages under osmotic stress that eventually help wheat breeding for drought tolerance. Moreover, there is a need that these wheat varieties be evaluated under field conditions.

ACKNOWLEDGEMENTS

This research was supported by the University Grants Commission of Bangladesh (Grant No. 2019/829/UGC).

Notes

AUTHOR CONTRIBUTIONS

AHKR planned and designed the experiments. SG executed the experiments. MAS assisted SG in data collection. SG and MAS wrote the manuscript. AHKR critically revised the manuscript.

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Fig. 1
Comparison of wheat varieties between control and PEG treatment based on shoot and root growth. (a) BARI Gom 25 under control and 10% PEG treatment, (b) seedling growth of Durum under control and 10% PEG treatment, (c) seedling growth of Kanchan under control and 10% PEG treatment, (d) seedling growth of Kalaysona under control and 10% PEG treatment.
PBB-8-174-f1.tif
Fig. 2
Treatment effect, varietal variation and treatment × variety interaction on percent germination of twenty two wheat varieties under 0% (control) and 10% polyethylene glycol treatments. Vertical bars indicate standard error of mean; different letters indicate significant difference among the treatment × variety interaction. In the graph, V1 = Durum, V2 = Sourav, V3 = Gourab, V4 = Sonalika, V5 = Kanchan, V6 = Sonora-64, V7 = Kalaysona, V8 = Triticale, V9 = Kheri, V10 = BARI Gom-21, V11 = BARI Gom-22, V12 = BARI Gom-23, V13 = BARI Gom-24, V14 = BARI Gom-25, V15 = BARI Gom-26, V16 = BARI Gom-27, V17 = BARI Gom-28, V18 = BARI Gom-29, V19 = BARI Gom-30, V20 = BARI Gom-31, V21 = BARI Gom32, V22 = BARI Gom-33.
PBB-8-174-f2.tif
Fig. 3
Treatment effect, varietal variation and treatment × variety interaction on shoot length of twenty two wheat varieties under 0% (control) and 10% polyethylene glycol treatments. Vertical bars indicate standard error of mean; different letters indicate significant difference among the treatment × variety interaction. In the graph, V1 = Durum, V2 = Sourav, V3 = Gourab, V4 = Sonalika, V5 = Kanchan, V6 = Sonora-64, V7 = Kalaysona, V8 = Triticale, V9 = Kheri, V10 = BARI Gom-21, V11 = BARI Gom-22, V12 = BARI Gom-23, V13 = BARI Gom-24, V14 = BARI Gom-25, V15 = BARI Gom-26, V16 = BARI Gom-27, V17 = BARI Gom-28, V18 = BARI Gom-29, V19 = BARI Gom-30, V20 = BARI Gom-31, V21 = BARI Gom-32, V22 = BARI Gom-33.
PBB-8-174-f3.tif
Fig. 4
Treatment effect, varietal variation and treatment × variety interaction on root length of twenty two wheat varieties under 0% (control) and 10% polyethylene glycol treatments. Vertical bars indicate standard error of mean; different letters indicate significant difference among the treatment × variety interaction. In the graph, V1 = Durum, V2 = Sourav, V3 = Gourab, V4 = Sonalika, V5 = Kanchan, V6 = Sonora-64, V7 = Kalaysona, V8 = Triticale, V9 = Kheri, V10 = BARI Gom-21, V11 = BARI Gom-22, V12 = BARI Gom-23, V13 = BARI Gom-24, V14 = BARI Gom-25, V15 = BARI Gom-26, V16 = BARI Gom-27, V17 = BARI Gom-28, V18 = BARI Gom-29, V19 = BARI Gom-30, V20 = BARI Gom-31, V21 = BARI Gom-32, V22 = BARI Gom-33.
PBB-8-174-f4.tif
Fig. 5
Treatment effect, varietal variation and treatment × variety interaction effect on root shoot ratio of twenty two wheat varieties under 0% (control) and 10% polyethylene glycol treatments. Vertical bars indicate standard error of mean; different letters indicate significant difference among the treatment × variety interaction. In the graph, V1 = Durum, V2 = Sourav, V3 = Gourab, V4 = Sonalika, V5 = Kanchan, V6 = Sonora-64, V7 = Kalaysona, V8 = Triticale, V9 = Kheri, V10 = BARI Gom-21, V11 = BARI Gom-22, V12 = BARI Gom-23, V13 = BARI Gom-24, V14 = BARI Gom-25, V15 = BARI Gom-26, V16 = BARI Gom-27, V17 = BARI Gom-28, V18 = BARI Gom-29, V19 = BARI Gom-30, V20 = BARI Gom-31, V21 = BARI Gom-32, V22 = BARI Gom-33.
PBB-8-174-f5.tif
Fig. 6
Treatment effect, varietal variation and treatment × variety interaction on oven dry weight of twenty two wheat varieties under 0% (control) and 10% polyethylene glycol treatments. Vertical bars indicate standard error of mean; different letters indicate significant difference among the treatment × variety interaction. In the graph, V1 = Durum, V2 = Sourav, V3 = Gourab, V4 = Sonalika, V5 = Kanchan, V6 = Sonora-64, V7 = Kalaysona, V8 = Triticale, V9 = Kheri, V10 = BARI Gom-21, V11 = BARI Gom-22, V12 = BARI Gom-23, V13 = BARI Gom-24, V14 = BARI Gom-25, V15 = BARI Gom-26, V16 = BARI Gom-27, V17 = BARI Gom-28, V18 = BARI Gom-29, V19 = BARI Gom-30, V20 = BARI Gom-31, V21 = BARI Gom-32, V22 = BARI Gom-33.
PBB-8-174-f6.tif
Fig. 7
Biplot of seedling traits of wheat varieties along with treatments. In the graph, V1 = Durum, V2 = Sourav, V3 = Gourab, V4 = Sonalika, V5 = Kanchan, V6 = Sonora-64, V7 = Kalaysona, V8 = Triticale, V9 = Kheri, V10 = BARI Gom-21, V11 = BARI Gom-22, V12 = BARI Gom-23, V13 = BARI Gom-24, V14 = BARI Gom-25, V15 = BARI Gom-26, V16 = BARI Gom-27, V17 = BARI Gom-28, V18 = BARI Gom-29, V19 = BARI Gom-30, V20 = BARI Gom-31, V21 = BARI Gom-32, V22 = BARI Gom-33.
PBB-8-174-f7.tif
Table 1
List of wheat varieties used this study along with their notable characteristics (BARI, http://baritechnology.org/en/home/tech_commodity#result).
Sl. No Variety name Given identity Year released Yield (t ha‒1) Characteristics
1 Durum V1 Tetra-ploid wheat - -
2 BARI Gom 19 (Sourav) V2 1998 3.5-4.5 Moderately heat tolerant
3 BARI Gom 20 (Gourab) V3 1998 3.6-4.8 Heat sensitive
4 Sonalika* V4 1974 3.0-3.5 Low yielding variety
5 Kanchan V5 1983 3.5-4.5 Low yielding variety
6 Sonora-64 V6 1974 1.6-2.2 Low yielding variety
7 Kalaysona V7 1974 2.6-3.2 Low yielding variety
8 Triticale V8 Hexa-ploid - -
9 Kheri* V9 Indigenous cultivar 2.0-2.5 Low yielding variety
10 BARI Gom-21 (Shatabdi) V10 2000 3.6-5.0 Good level of tolerance to terminal heat stress
11 BARI Gom-22 (Sufi) V11 2005 3.6-5.0 Tolerant to late heat stress
12 BARI Gom-23 (Bijoy) V12 2005 4.3-5.0 Moderately heat tolerant
13 BARI Gom-24 (Prodip) V13 2005 4.3-5.1 High yielding, but heat sensitive
14 BARI Gom-25 V14 2010 3.6-5.0 Moderate level of tolerance to heat stress
15 BARI Gom-26 V15 2010 3.6-5.0 Tolerant to terminal heat stress in late seeding
16 BARI Gom-27 V16 2012 4.0-5.4 Moderate level of tolerance to heat stress
17 BARI Gom-28 V17 2012 4.0-5.5 Tolerant to terminal heat stress in late seeding
18 BARI Gom-29 V18 2014 4.0-5.0 Moderately tolerant to terminal heat stress
19 BARI Gom-30 V19 2014 4.5-5.5 Resistant to stem rust race, Ug 99 and leaf rust and moderately resistant to Bipolaris leaf blight disease
20 BARI Gom-31 V20 2017 4.5-5.0 Resistant to leaf rust and moderately resistant to Bipolaris leaf blight disease
21 BARI Gom-32 V21 2017 4.6-5.0 High yielding, early in maturity and tolerant to terminal heat stress, leaf rust and tolerant to Bipolaris leaf blight disease
22 BARI Gom-33 V22 2017 4.0-5.0 Zn enriched (55-60 ppm) and tolerant to wheat blast disease
Table 2
Analysis of variance of germination and seedling traits of wheat varieties under PEG stress.
Sources of variation df Mean squares

PG (%) SL RL R/S ODW
Treatment (T) 1 245.4** 1942.3*** 24.6*** 113.4*** 0.0048***
Variety (V) 21 196.1*** 8.51*** 4.79*** 0.248 0.00014***
T × V 21 32.76 6.39** 1.80 0.237 0.00004
Error 88 27.27 2.87 1.41 0.23 0.000037

* , **, and ***Significant at 0.05, 0.01, and 0.001 probability levels, respectively. df: degrees of freedom, PG (%): germination percentage, SL: shoot length, RL: root length, R/S: Root/Shoot, DW: dry weight.

Table 3
Mean performances of germination and seedling traits of wheat varieties under PEG stress.
Variety Identity PG (%) SL (cm) RL (cm) R/S ratio DW (g)
Durum V1 81.67 c 5.30 a-d 3.23 bc 1.24 a 0.02 c
Sourav V2 100.0 a 4.61 a-d 2.93 c 1.18 a 0.03 a-c
Gourab V3 98.33 a 3.33 cd 2.93 c 1.66 a 0.02 b-c
Sonalika V4 98.33 a 7.27 ab 5.78 ab 1.44 a 0.02 a-c
Kanchan V5 95.00 ab 4.20 a-d 3.28 bc 1.65 a 0.02 a-c
Sonora-64 V6 98.33 a 4.58 a-d 3.13 c 1.46 a 0.02 c
Kalaysona V7 90.00 a-c 2.83 d 2.73 c 1.43 a 0.02 c
Triticale V8 81.67 c 5.74 a-d 3.27 bc 1.76 a 0.04 a
Kheri V9 86.67 bc 5.53 a-d 3.13 c 0.99 a 0.02 c
BARI Gom-21 V10 100.0 a 5.98 a-d 3.66 a-c 1.27 a 0.02 a-c
BARI Gom-22 V11 91.67 a-c 6.53 a-c 3.97 a-c 1.50 a 0.02 c
BARI Gom-23 V12 100.0 a 4.73 a-d 3.88 a-c 1.39 a 0.02 a-c
BARI Gom-24 V13 95.00 ab 4.13 b-d 3.59 a-c 1.59 a 0.03 a-c
BARI Gom-25 V14 96.67 ab 6.11 a-d 3.33 bc 1.20 a 0.02 a-c
BARI Gom-26 V15 100.0 a 6.70 a-c 4.59 a-c 1.11 a 0.03 a-c
BARI Gom-27 V16 98.33 a 5.91 a-d 4.87 a-c 1.51 a 0.02 a-c
BARI Gom-28 V17 96.67 ab 5.49 a-d 3.44 bc 1.14 a 0.03 a-c
BARI Gom-29 V18 100.0 a 6.05 a-d 4.03 a-c 1.57 a 0.03 a-c
BARI Gom-30 V19 98.33 a 7.82 a 6.03 a 1.37 a 0.02 bc
BARI Gom-31 V20 100.0 a 5.32 a-d 4.35 a-c 1.30 a 0.02 a-c
BARI Gom-32 V21 98.33 a 5.76 a-d 4.71 a-c 1.63 a 0.02 a-c
BARI Gom-33 V22 98.33 a 5.35 a-d 4.27 a-c 1.35 a 0.03 ab

PG (%): germination percentage, SL: shoot length, RL: root length, R/S: Root/Shoot, DW: dry weight. Different letters indicate significant variation among varieties.

Table 4
Principal component analysis (PCA) of selected seedling traits of wheat varieties under PEG stress.
Variable PC1 PC2 PC3 PC4
Percent germination 0.201 ‒0.727 ‒0.642 ‒0.117
Shoot length 0.585 0.021 0.187 0.299
Root length 0.362 ‒0.485 0.671 ‒0.256
Root shoot ratio ‒0.54 ‒0.22 0.238 ‒0.509
Dry weight ‒0.441 ‒0.433 0.214 0.757
P (treatment) < 0.001 < 0.001 0.116 0.011
P (genotype) < 0.001 < 0.001 0.025 0.003
P (treatment × genotype) 0.59 0.72 0.015 0.30
Eigenvalue 2.57 1.02 0.84 0.47
% variation explained 51.4 20.5 16.9 9.4
Table 5
Pearson correlation analysis of germination and seedling traits of wheat varieties under PEG stress.
Percent germination Shoot length Root length Root shoot ratio
Shoot length 0.174*
Root length 0.196* 0.582***
Root shoot ratio ‒0.213* ‒0.813*** ‒0.215*
Dry weight ‒0.088NS ‒0.525*** ‒0.166NS 0.572***

* , **, and ***Significant at 0.05, 0.01, and 0.001 probability levels, respectively. NS: Non-significant.

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