Grain yield, chlorophyll and protein contents of elite wheat genotypes under drought stress

2.1 Experimental site

A field experiment was performed during 2019–20 at Wheat Research Institute (WRI), Faisalabad, Pakistan (31.405286 °N, 73.048130 °E with an elevation of 184 m above sea level). The texture of soil of experimental site was sandy clay loam. The soil characteristics of the experimental site are presented in Fig. 5. The maximum total rain fall was noted during the month of March 2020 which was 143 mm as shown in Fig. 4.

2.2 Experimental design and treatments

A set of 14 genotypes of bread wheat was used in the study to investigate their behavior under irrigated and drought conditions. The variety code and parentage of fourteen genotypes elaborated in Table 1. Randomized complete block design (RCBD) was adopted with three replications in this study. The plot size for each entry was 5 m × 1.62 m (8.1 m²). All the recommended cultural and agronomic practices were adopted. The data relating to days to 50 % heading, days to 50 % maturity, grain filling duration, plant height (cm), number of spikes per m², chlorophyll index (SPAD), peduncle length (cm), spike length (cm), number of grains spike^-1, number of spikelet spike^-1, thousand grain weight (g), protein content (%) and grain yield kg ha⁻¹ were recorded.

2.3 Statistical analysis

The recorded data of all the traits were analyzed using Statistix software (Version 8.1.) The means value of all the treatments were compared using Tukey’s HSD test at 5 % probability level (Steel et al., 1997). Pearson’s correlation was estimated for the identification of best correlated yield trait. Principal component analysis was performed as discussed by Curry et al. (1983) and followed by Abbas et al. (2022).

3.1 Analysis of variance and means comparison of data

Highly significant differences were found among all genotypes for studied traits (Table 2). These significant differences among all traits indicated the presence of great variability that can play a vital role in grain yield enhancement of bread wheat in different breeding programs. The range of coefficient of variance was 0.4 to 4.9 % in irrigated conditions, while 0.7 to 6.4 % in drought conditions.

The response of each bread wheat genotype for all the parameters under study under irrigated and drought conditions is presented in Table 3. In irrigated conditions, days to 50 % heading (DH) ranged from 112.0 to 119.0 days. The genotypes ‘V-19618′, ‘V-19574′ and ‘V-19504′ took lesser number of days for spike appearance compared to the rest of the genotypes included in the study. Under drought conditions, DH ranged from 109.0 to 115.0 days and genotypes ‘V-19600′, ‘V-19589′ and ‘V-19531′ resulted in early heading. Grain filling duration (days) varied from 34 to 39 in irrigated conditions with genotypes ‘V-19550′ and ‘V-19602′ taking lesser days to fill the grain. Grain filling duration (days) ranged from 29.0 to 37.0 days under drought stress with the genotypes ‘V-19550′ and ‘V-19554′ took less days to fill the grain. Significant variability was noted for days to 50 % maturity (DM) under both conditions. The DM varied between 150.0 and 154.0 and 142.0 to 148.0 days under irrigated and drought conditions, respectively. Genotype ‘V-19618′ under irrigated conditions and ‘V-19554′ under drought conditions proved early maturing. Plant height (PH) ranged from 85.0 to 106.0 and 79.0 to 103.0 cm under irrigated and drought conditions, respectively. Genotype ‘V-19600′ was the shortest and ‘V-19602′ was the tallest. Significant variation was found for number of tillers per m². Number of tillers per m² ranged from 459.0 to 570.0 and 229.3 to 362.3 under irrigated and drought conditions, respectively. Genotype ‘V-19554′ under irrigated condition and ‘V-19602′ under drought conditions produced the highest number of number of tillers per m². The chlorophyll index (SPAD) varied from 47.0 to 52.0 and 50.0 to 54.0 in irrigated and drought conditions, respectively. Genotype ‘V-19554′ under irrigated and ‘V-19574′ under drought conditions resulted in the highest chlorophyll index. Under irrigated conditions peduncle length ranged from 14.7 to 23.8 cm and under drought condition it ranged from 11.5 to 16.0 cm. Genotype ‘V-19574′ had the highest peduncle length under both conditions.

Spike length varied from 5.3 to 6.9 cm under irrigated conditions and genotype ‘V-19550′ produced the longest spikes. On the other hand, spike length under drought conditions ranged from 5.2 to 6.8 cm and genotype ‘V-19618′ produced the longest spike. Number of grains spike^-1 varied from 34.0 to 50.0 and 21 to 35.3 under irrigated and drought conditions, respectively. Genotype ‘19600′ produced the highest number of grains among all genotypes under both irrigated and drought conditions. The number of spikelets per spike^-1 varied from 14.0 to 17.7 under irrigated and 14.3 to 17.7 under drought conditions. Under both conditions genotype ‘V-19600′ produced the higehst number of spikelets per spike^-1. Under irrigated condition thousand grain weight ranged from 36.6 to 47.9 g, while under drought it ranged from 26.4 to 40.6 g. Genotype ‘V-19565′ under irrigated conditions and ‘V-19618′ under drought conditions produced the heaviest thousand grains. Protein contents ranged from 12.5 to 14.0 % and 14.8 to 16.1 % under irrigated and drought conditions, respectively. Genotypes ‘V-19618′ had the highest protein content under both environments. Grain yield ranged between 3352 and 5550 kg ha⁻¹ under irrigated conditions, while it varied from 2276 to 3416 kg ha⁻¹ under drought conditions. Genotype ‘V-19554′ under irrigated conditions and ‘V-19618′ under drought stress produced the highest grain yield.

Drought stress is a major factor among other environmental stresses which can cause significant yield losses by affecting crop growth and productivity (Pour-Aboughadareh et al., 2019). Generally, drought stress leaves negative effects on physiological and agronomic characters in wheat crop (Qaseem et al., 2019). The mean data (Table 3) of wheat genotypes under irrigated and drought conditions indicated a decline in yield and related traits. Gaju et al. (2009) and Pour-Aboughadareh et al. (2020) also reported similar trend. However, protein contents under both the conditions observed a positive jump under drought stress (Kilic and Yağbasanlar, 2010). Previous studies also discussed reduction in grain yield due to drought stress (Etminan et al., 2019).

3.2 Association between measured traits

The association among recorded traits under both environments was assessed using Pearson’s correlation as adopted by Pour-Aboughadareh et al. (2020). Under drought conditions, grain yield showed highly significant positive correlation with thousand grain weight, number of spikes per m², and spike length. On the other hand, chlorophyll index, grain filling duration, and number of grains spike^-1 showed significant positive relation with grain yield. Baye et al. (2020) also reported positive correlation of grain yield with grain filling period, grains spike^-1 and thousand grain weight in wheat. The higher value of chlorophyll index is prediction of good grain yield in wheat (Islam et al., 2014). The non-significant and positive correlation was found among days to 50 % maturity, protein content, peduncle length and spikelets per spike^-1 with grain yield under drought condition, while non-significant negative relationship of grain yield was observed with plant height (Fig. 1). Days to 50 % heading expressed significant but negative correlation with grain yield under drought condition. Similar findings have also been explained by Mecha et al. (2017).

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Fig. 1

Phenotypic Correlation of wheat genotypes for yield and quality traits in Drought conditions (below diagonal) and Irrigated (above diagonal). CC = chlorophyll index (SPAD), DG = grains filling duration (days), DH = days to 50 % heading, DM = days to 50 % maturity, GS = number of grains spike^-1, GW = 1000 grain weight (g), GY = grain yield (kg ha⁻¹), NS = number of spike per m², PC = protein content (%), PH = plant height (cm), PL = peduncle length (cm), SL = spike length (cm), SP = number of spikelet spike^-1,

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In irrigated condition the relationship of chlorophyll index, thousand grain weight, number of spikes per m² and peduncle length had highly significant positive correlation with grain yield, while grain filling period and number of grains spike^-1 expressed significant positive correlation with grain yield. Spike length and number of spikelets spike^-1 showed non-significant and positive correlation, while days to 50 % maturity, protein contents (%) and plant height showed non-significant but negative relationship with grain yield.

3.3 Principal component analysis

Principal component analysis (PCA) separated the total variance into several factors which are useful for conservation and manipulation of genetic resources and planning for utilization of appropriate germplasms in crop improvement (Zaman et al., 2014). The biplot expressed the association among different measured traits and wheat genotypes. Biplot vectors closer to each-other showed the correlation between those traits and the genotypes close to a specific trait vector represents the best performance of the wheat genotypes for that particular plant trait (Zulkiffal et al., 2018).

The biplot of PCA1 and PCA2 for irrigated (Fig. 2) and drought condition (Fig. 3) indicates the relationships between different indices. Differentiation indices in different groups was found due to PCA1 and PCA2 under both the conditions. The first and second components justified 65.4 % and 62.6 % variation between the criteria under irrigated and drought conditions, respectively.

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Fig. 2

PCA biplot of wheat Genotypes under irrigated conditions. V1 = V-19503, V2 = V-19504, V3 = V-19521, V4 = V-19531, V5 = V-19542, V6 = V-19550, V7 = V-19554, V8 = V-19565, V9 = V-19566, V10 = V-19574, V11 = V-19589, V12 = V-19600, V13 = V-19602, V14 = V-19618.

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Fig. 3

PCA biplot of wheat genotypes under drought conditions. V1 = V-19503, V2 = V-19504, V3 = V-19521, V4 = V-19531, V5 = V-19542, V6 = V-19550, V7 = V-19554, V8 = V-19565, V9 = V-19566, V10 = V-19574, V11 = V-19589, V12 = V-19600, V13 = V-19602, V14 = V-19618.

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Fig. 4

Meteorological data of the experimental site during 2019–20.

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Fig. 5

Characteristics of soil of the field trial site.

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The PCA biplot under irrigated conditions (Fig. 2) revealed positive association of grain yield with chlorophyll index, thousand grain weight, number of spikes per m², peduncle length, grain filling duration, number of grains spike^-1, spike length (cm) and number of spikelets spike^-1. However, plant height (cm), protein contents (%), days to 50 % maturity and 50 % heading expressed negative relationship with grain yield. Genotype ‘V-19574′ proved the best genotype under irrigated conditions regarding grain yield and related traits.

Under drought stress, PCA biplot showed positive relationship of grain yield with thousand grain weight, number of spikes per m², spike length (cm), chlorophyll index, grain filling period and number of grains spike^-1. On the other hand, negative relationship was found regarding days to 50 % heading and 50 % maturity, protein content, peduncle length, and number of spikelets spike^-1. Genotypes ‘V-19618′, ‘V-19574′ and ‘V-19600′ proved best genotypes under drought conditions regarding grain yield and related traits.