Genetic Control of Tropical Maize Grain Yield Under Stress and Non-Stress.

The objective of this work is to study the genetic control of tropical maize grain yield under non-stress and stress environments. Thus, a diallel was performed among commercial corn cultivars. The trials were conducted at two locations during the agricultural years of 1999/00 and 2000/01. The experimental design used was randomized blocks with two repetitions. The significance of the environment effect characterized the environments as contrasting. Based on grain yield averages, the environments were classified as: environment 1 (8.331 kg ha^-1), favorable; environments 2 (6.637 kg ha^-1) and 3 (5.495 kg ha^-1), intermediary; and environment 4 (2.443 kg ha^-1), under intense stress. On environments 1 and 4, none of the genetic effects was significant. It showed that exist low genetic variability to these situations. In environments 2 and 3, significance was verified for the specific combining ability effect (SCA), showing that the nonadditive genetic effects were the most important and that it is possible to select parents with breeding potential. The SCA x environment interaction indicated that the actions of the nonadditive genetic effects and SCA were significantly influenced by the environmental changes. SCA and grain yield showed significant correlations only between the environment pairs 1 x 2 and 3 x 4. For environments 1 x 4 and 2 x 4, SCA showed significant negative correlations. Thus, it was concluded that grain yield genetic control differed under contrasting environments regarding stress intensity and that the nonadditive genetic effects are the most important for intermediary stress environments.