Heat stress impact and genetic diversity among some bread wheat genotypes

Wheat is the most widely grown crop in the world especially in the developing countries. Recently, the climatological extremes including high temperatures is predicted to have a general negative effect on wheat production due to the damaging effect on plant development especially during anthesis stage. Heat tolerance is a complex trait and influenced by different components. A panel of 40 wheat genotypes were evaluated for 8 yield and yield-contributing traits under recommended sowing date of the Egyptian ministry of agriculture as a control and two other different sowing dates as plants will face heat-stressed conditions at anthesis and grain-filling phases. All measured phenotypic traits exhibited highly significant differences both among evaluated accessions and sowing dates in both growing seasons. A continuous phenotypic variation in all measured traits were found, indicating a polygenic inheritance of measured traits. The ANOVA revealed highly significant genotype × environment interaction which is expected for quantitative traits. Cluster analysis revealed two distinct groups with respect to stress tolerance index with substantial diversity among genotypes either susceptible or tolerant to heat stress. Cophenetic correlation between ultrametric similarities of tree and similarity matrix was found to be relatively high (r = 0.76, P < 0.01), suggesting that the cluster analysis strongly represents the similarity matrix.