Effect of terminal drought stress on some agronomic traits of 20 elite bread wheat genotypes

Identification and introduction of drought stress tolerant cultivars has always been a high priority in agricultural research. Investigating and comparing genotypes in terms of yield and other important agronomical traits under different environmental conditions is one of the primary and important steps to achieve this goal. Therefore, the aim of this study was to investigate the terminal drought stress on some agronomic traits of 20 bread wheat genotypes, studying the agronomical and physiological response of the genotypes and also identifying the suitable genotype to be nominated for planting in areas with terminal drought stress.

At this research, 20 bread-wheat genotypes including cultivars and elite lines were evaluated using Randomized Complete Blocks Design (CRBD) with three replicates under non-stress and terminal drought stress conditions at Islamabad-e-Gharb Agricultural Research Station (Kermanshah Agriculture and Natural Resources Research and Education Centre) during 2011-2012 cropping year. Each plot consisted of six 6 meter rows with 22.5 cm row spacing (plot size 7.2 m2). Plots were machine-drilled by Wintersteiger plot seeder with 400 seeds per square meter density. Irrigation was carried out in non-stress conditions for all genotypes until the physiological maturity stage. But in the stress conditions, irrigation continued until the booting stage and then cut off and non-irrigation continued until the end of the growing season. During the growing season, the traits were evaluated and measured. At full physiological maturity, all the rows of each plot were machine-harvested by small-plot combine (Wintersteiger harvester).

Simple ANOVA exhibited non-significant differences among the genotypes for all studied traits under both non-stress and terminal drought stress conditions. The result of the combined analysis of variance indicated there is no significant difference among genotypes for all of the studied traits except grain number per spike, peduncle length, penultimate length and day to physiological maturity. The effect of environment (drought stress) was significant on all studied traits except for biological yield, the number of kernels per spike and peduncle length. The stress intensity in this study was 0.55. Drought stress reduced the average of all studied traits except peduncle length. However, it had the highest effect on kernel yield by 55.36% reduction. The genotype × environment was not significant for any of the traits. The mean kernel yields of the genotypes were 8955 and 3997 kg/ha under non-stress and stress condition, respectively. Correlations of kernel yield with penultimate length and hectolitre weight were positive and significant at 1% and 5% probability levels, respectively. Genotypes 13, 20, 8, 9, 5 and 6 were identified as the most tolerant genotypes based on the ranking method and the principal components analysis.

Most of studied traits, especially kernel yield, were significantly affected by drought stress. Drought stress had the highest effect on kernel yield by 55.36% reduction. The results showed that in order to evaluate drought stress tolerance, selection of genotypes should be based on several indices or based on the average of the indices rating. Therefore, genotypes 13, 20, 8, 9, 5 and 6 were identified as the most tolerant genotypes based on the ranking method. These genotypes were also identified as the superior genotypes based on biplot diagrams under both non-stress and terminal drought stress conditions. These genotypes can be used in breeding programs in order to produce new bread wheat tolerant cultivars. Genotypes 14, 18, 15, 10 and 11 can be suggested for irrigated and non-stress conditions. The study of drought tolerance indices showed that MP, GMP, STI, HAM, K1STI and K2STI have better efficiency for selection of high yielding and tolerant genotypes.