Estimation of Combining Ability for Earliness and Morpho-Physiological Traits of some Bread Wheat Genotypes under Optimum and Late Sowing Dates

Using a half-diallel model, six genotypes of bread wheat were crossed during 2021/2022 season, to determine the genetic effects. Parents and their F1 were examined utilizing a randomized complete block design (RCBD) with 3 replications under optimum and late sowing dates in the 2022/2023 season on the research farm of the agronomy division, faculty of agriculture, Mansoura University,Dakahlia Governorate, Egypt. Data were taken on the earliness and physiological characteristics. Results revealed that the variance of sowing dates were significant for every examined attribute except for total chlorophyll content.The sowing date × genotypes interactions were found to be significant for every attribute except for grain filling rate.The variance of general (GCA) and specific (SCA) combining ability were significant for every examined attribute at each sowing date except for days to maturity, grain filling period, grain filling rate under late sowing date, and chlorophyll content under late sowing date due to SCA. GCA/SCA ratio was more than unity for days to heading, days to anthesis and flag leaf area under optimum sowing date, days to maturity and chlorophyll under content late sowing date, grain filling period, grain filling rate under optimum and late sowing date, it means that the control of these traits was more dependent on additive genetic impact.Results showed that crosses P1xP3, P3xP4 and P5xP6 exhibited significant and negative SCA effects, heterosis and heterbeltiosis for most earliness traits under study.Therefore, we can recommend introducing these hybrids into the wheat breeding program to increase productivity, whether in early or late planting.