Thirty diverse genotypes of bread wheat were evaluated for seed vigour index, germination percentage, root length, shoot length, root-to-shoot length ratio, coleoptile length and osmotic membrane stability under laboratory conditions. Considerable variation was observed for all the characters. Discrimination among the genotypes on the basis of mean values was better under normal than under moisture stress conditions, indicating suppression of variability under moisture stress conditions. Comparison of mean performance under normal and osmotic stress conditions indicated that the seed vigour index was the most sensitive trait, followed by shoot length, germination percentage and root length. The root-to-shoot length ratio, however, increased under osmotic stress. The magnitude of genetic components of variance and heritability were, in general, lower under osmotic stress than under normal conditions. All the characters except germination percentage, shoot length and coleoptile length showed considerable genetic variability. Heritability in the broad sense was also moderate to high for all the characters under both environments. Due to high heritability and genetic advance great benefit from selection can be expected for the osmotic membrane stability of leaf segments and root-to-shoot length ratio. Moderate progress can be expected from root length and seed vigour index. Correlation studies indicated that the osmotic membrane stability of the leaf segment was the most important trait, followed by root-to-shoot ratio and root length on the basis of their relationships with other traits.
Experiments were designed to examine differences in some morpho-physiological characters among wheat genotypes in response to drought stress at anthesis and maturity and to determine the relationships between these characters. In three sets of experiments, one set was evaluated under well-irrigated conditions and two sets under drought stress conditions by developing terminal drought stress at anthesis in one set and at maturity in the other, for 2 years. Genotypes differed in their response at both stages of plant growth for grain yield, days to heading, excised-leaf water loss, leaf membrane stability and relative water content under drought stress. Under irrigated conditions differences in the genotypes for water retention traits were not clear. There were significant genotype×environment interactions. Terminal drought stress resulted in reduced mean values and variability for all characters. The varieties WH 147 and WH 147(U) showed a combination of drought resistance, water retention and high grain yield, whereas C 306, Kharchia 65 and Hindi 62 showed a lower percentage injury in plasma membrane and better water retention in the leaves. Drought resistance index was associated with other characters.
Leaf membrane stability (LMS) and the tetrazolium triphenyl chloride (TTC) test, heat susceptibility index (HSI), heat response index (HRI) and grain yield were used to evaluate 20 diverse wheat genotypes under normal and heat stress conditions for 2 years. The varieties ÔSeriÕ and ÔRaj 3765Õ had a desirable combination of cellular thermotolerance (TTC and LMS), heat tolerance (HRI) and high grain yield potential under heat stress, while ÔWH 730Õ and ÔWH 533Õ were better in cellular thermotolerance and heat tolerance. The varieties ÔPBW 373Õ and ÔKauzÕ also performed better under heat stress in terms of grain yield and HSI/ HRI. The varieties ÔKanchanÕ, ÔPBW 373Õ, ÔNIAW 34Õ and ÔGW 173Õ were avoiders/escapers, ÔSeriÕ and ÔHUW 234Õ were tolerant to heat stress, while ÔWH 730Õ, ÔWH 533Õ, ÔNesserÕ, ÔRaj 3765Õ and ÔKauzÕ showed a combination of both. Correlation coefficients revealed that HRI was the most important trait, followed by TTC because the genotype having high HRI also had high grain yield and was better in mitochondrial viability and membrane stability under heat stress. Significance of GCA and SCA variances indicated the presence of both additive and dominant types of gene action. The use of the parents with high GCA effects, namely, ÔRaj 3765Õ and ÔWH 730Õ in a crossing programme for thermotolerance may provide desirable segregants through selection.
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