Impacts of Selection for Spike Length on Heat Stress Tolerance in Bread Wheat ( Triticum aestivum L.)

Two consecutive cycles of selection were imposed on five F2 populations of bread wheat. The first cycle was a divergent selection for spike length conducted in favorable environment (optimal sowing date) and the response was measured under favorable and heat stress conditions of a late sowing date. Positive responses to selection for longer spikes were obtained under favorable (13.43%) heat stress (8.66%) conditions, whereas the responses for shorter spikes were 2.24 and 5.02% in the two environments, respectively. The realized heritability of spike length was greater under favorable conditions (0.25-0.56) than under heat stress (0.18- 0.41). Concurrent positive responses to selection for longer spikes were obtained in grain yield per spike under favorable (25.35%) and heat stress (13.65%) environments. Selection for greater number of grains per spike imposed on F3 plants selected for spike length under heat stress resulted in significant responses (14.65%). Selection for greater number of grains per spike resulted in correlated responses in grain yield per spike (17.64%). The concurrent positive responses produced in spike length in F4 with selection for number of grains per spike (averaged 9.20%) was almost equal to that produced by the direct selection in F3 (8.66%), indicating that selection advance effected in F3 has been maintained in F4. High F4/F3 regression was obtained for spike length under heat stress (b = 0.85 ± 0.07), indicating high heritability. In conclusion, phenotypic selection for longer spikes under heat stress followed by a cycle of selection for number of grains per spike was capable of improving heat tolerance in wheat. KCI Citation Count: 0