YIELD RESPONSE OF SPRING WHEAT CULTIVARS AT DIFFERENT IRRIGATION RATES

We found in a previous study that Brazilian tall cultivars of spring w heat (Triticum aestivum L.) were more resistant to drought in respect of photosynthesis as compared to Mexican and Japanese semidwarf cultiv ars. In this study, a yield trial was performed with the same 20 culti vars to elucidate the yield and yield component responses to the soil water conditions in Cerrados, a semiarid region of Brazil. Under dry c onditions, the dry matter yield of the Brazilian cultivars was signifi cantly higher than the yields of the Mexican and Japanese cultivars. T he grain field of the Brazilian cultivars was also 34-46% greater than those of the Mexican and Japanese cultivars. Under fully-irrigated co nditions, however, the Mexican and Japanese cultivars showed higher ha rvest indices and 18-21% greater grain yield than the Brazilian cultiv ars, although no practical difference was found among the cultivar gro ups in terms of dry matter yield. An analysis of yield components show ed that the Brazilian cultivars had a larger 1000 kernel weight than t he Mexican and Japanese cultivars under dry conditions, while the Mexi can and Japanese cultivars had a higher kernel number than the Brazili an cultivars under fully-irrigated conditions. The reverse rotation of yield ranking among the cultivars under non-irrigated and fully-irrig ated conditions is due to the fact that the Mexican and Japanese culti vars are more sensitive to soil moisture than the Brazilian cultivars.