Abstract
Commercial hybrids are the main germplasm source for developing maize lines in breeding programs in Brazil; additionally, nitrogen (N) is one the major limiting maize production in Brazilian tropical areas. Here, we assessed the combining ability among ten commercial hybrids under contrasting N inputs and selected the best parental hybrids to develop breeding populations for optimal and N-stress environments. We evaluated the 45 F1 crosses for agronomic traits under contrasting N inputs and over two summer seasons. A mixed model approach was used to estimate the variance components of general combining ability (GCA) and specific combining ability (SCA) as well as to predict the GCA and SCA effects. N-stress caused a reduction in GY (33.25%) of F1 crosses averaged across seasons. We found presence of combining ability (GCA and SCA) x N input interaction for grain yield (GY), days to pollen and plant stature. The parental hybrids showed differences in GCA for cycle and plant stature but not for GY, irrespective of N inputs. Additionally, the variance components of SCA were not significant (P>0.10) for GY under LN, whereas SCA was the major component accounting for variation among F1 crosses under HN. Based on estimates of GCA effects for cycle and plant height, we selected the hybrids BAL188, BM3061, GNZ7210, BRS1060 and DKB390 as sources of favorable alleles for earlier maturing and shorter stature maize for both N conditions and suggested that hybrids GNZ7201 and DKB390, and AG1051 and NS70, which presented very small estimates of SCA for GY, must be recombined to develop two synthetic populations to begin a reciprocal recurrent selection program, mainly for non N-stress environments.