IMPACT OF SELECTION FOR STOMATA FREQUENCY ON YIELD CHARACTERISTICS UNDER HEAT AND DROUGHT STRESSES IN BREAD WHEAT (Triticum aestivum L).

Stomata spread allover leaves are important sources for plant canopy temperature depression which might contribute to heat stress tolerance. Two F₂ populations of bread wheat (Triticum aestivum L.) were subjected to two cycles of divergent selection for flag leaf stomata frequency. Plants were exposed to heat and drought stresses in order to study the impact of selecting for high and low stomata frequency on yield characteristics. The correlated responses in grain yield/plant and 100-kernel weight were determined.









 





 



The response to the first cycle of selection in the high direction in population 1 and 2 amounted to 16.03% and 11.63% of the bulk sample mean, respectively, which were consistently higher than that expected (8.29% and 5.598%). Higher observed response (7.16%) than expected (5.50%) was also observed for low stomata frequency in population 2. Such inflated responses might be attributed to dominance, epistasis or G x E. Asymmetrical responses to selection were evident with the deviation being greater in the high direction. Narrow-sense heritability, as calculated by parent-offspring regression, reached 0.45 and 0.266 in populations 1 and 2, respectively. However, the realized heritability was higher in the high direction than that in the lower direction in both populations.
The observed responses of the second cycle of selection amounted to 12.71% and 9.39% from the bulk mean were greater than those expected (9.48% and 5.01%) in populations 1 and 2, respectively. In the low stomata frequency direction the observed responses (6.67% and 9.42%) were also higher than those expected (5.32% and 3.63%). Generally, the differences between high and low directions were highly significant over cycles of selection for both populations. The narrow-sense heritabilities were 0.50 and 0.36 in population 1 and 2, respectively. The realized heritability reached 0.62 and 0.44 in the low and high directions, respectively in population 2, while it remained unchanged in population 1. Further expected responses of 7.04% and 9.61% in the low and high directions, respectively in population 1, and of 5.60% and 6.58% in the low and high directions, respectively in population 2 under heat and drought stresses were estimated for the third cycle of selection.
The selected F₄ families of population 1 developed significantly higher 100-kernel weight but lower grain yield/plant than population 2 in the low and the high direction as well as the two bulks. Such differences were only observed in the high direction where selection led to greater mean of stomata frequency in population 1 than in population 2. Selecting for stomata frequency did not show correlated responses in 100-kernel weight or in grain yield/plant. No correlated responses were detected for leaf area, which did not differ among selected families and the control or the other studied traits.