Genetic analysis of thermotolerance and grain yield traits of bread wheat (Triticum aestivum L.) Using diallel analysis

Heat stress alters the wheat crop productivity, causes a catastrophic loss of global wheat productivity. This study aims to find knowledge on genetic analysis of thermotolerance bread wheat genotypes altered by heat stress. Six bread wheat genotypes were crossed using a half-diallel producing 15 F1 crosses. All genotypes were sown in two different sowing dates (optimal sowing date 22nd November', and late sowing date `5th January') producing different heat stress conditions at two grown seasons 2015/2016, and 2016/2017 at Faculty of agriculture Farm, Zagazig University, Egypt. To investigate the thermotolerance and grain yield genetic analysis, we studied some physiological traits; days to heading and maturity, and two yield traits; 1000 grain weight and grain weight. Results indicate a significant difference between all the genotypes performance. Consequently, a reduction in all the studied traits is found under the heat stress conditions; days to heading (17.12Y) and maturity (16.96`)/0), 1000 -grain weight (25.67/0) and grain weight (56.62`)/0). Studying the combining ability, results reveal that, both general `GCA' and specific 'SCA' are presence high significant values. GCA/SCA ratio is above unity for days to heading, maturity, while it is less than unity for 1000 grain weight and grain yield/plant on the two sowing dates. It is noticed a low narrow sense heritability for all studied traits; while it is moderate for days to maturity. Covariance/Variance analysis discloses non -additive gene action with overdominance for all studied traits on the two sowing dates except days to maturity inherited by complete dominance. In conclusion, genotypes; Misr 1, Sids 14 and their F1 cross, are considered more thermotolerance corresponding to their yield under heat stress. Furthermore, they show negative and significant SCA. These results show new insights on the economic traits of the wheat crop productivity breeding program under the alterations on the climate changing. Furthermore, new genotypes candidates are identified as an ideal material for future thermotolerance breeding programs.