Genetic variability and association of yield and yield components among bread wheat genotypes under drought-stressed conditions

Drought is one of the major constraints to wheat production and productivity globally. Developing drought-adapted wheat cultivars is paramount to increase wheat productivity under variable rainfall conditions. Understanding the genetic variability and trait association is key to the development of improved wheat cultivars. The objective of this study was to determine the extent of the genetic parameters and associations of yield and yield components of bread wheat genotypes, in order to design appropriate breeding strategies for yield improvement in wheat. One hundred and twenty genotypes were evaluated at five test sites in the 2018/19 cropping season using a 10 x 12 alpha lattice design with two replications. Different sowing dates were used to impose contrasting drought stress levels based on the onset of the main seasonal rains at each site. Data were recorded on agronomic traits such as days to heading (DH), days to maturity (DM), plant height (PH), spike length (SL), spikelet per spike (SS), kernel per spike (KS), 1000 kernel weight (TKW) and grain yield (GY). There was significant (p<0.01) genetic variation for all agronomic traits studied under both drought-stressed and non-stressed conditions. The highest estimates for genetic variance were obtained for DH (54.0%), followed by SL (38.3%). The high heritability estimated for DH (94.4%), SL (90.2%) and SS (85.2%), coupled with a high rate of genetic advance, suggest that direct selection for these traits would be effective under drought-stressed conditions. GY exhibited low genetic advance (9%) and heritability (41.5%) estimates, which were concomitant with its polygenic and complex inheritance pattern. Correlation and path analyses revealed that TKW was the most important contributing trait for improving grain yield under drought-stressed conditions