Inheritance of root morphology in tropical maize under contrasting nitrogen levels

The development of improved low-nitrogen (N) tolerant and N-efficient varieties of tropical maize can be achieved by improving root morphology traits, but little is known on the inheritance of root traits in tropical maize, especially under low-N stress. Thus, our main objective was to assess the inheritance of seedling root and shoot traits in tropical maize under contrasting N levels. We evaluated 45 F 1 and 45 reciprocal crosses (90 total crosses) along with ten parental inbred lines of tropical maize for root and shoot traits under contrasting N levels: low N (LN) and high N (HN). A mixed model approach was used to estimate the variance components of the general (GCA), reciprocal general (RGCA), specific (SCA) and reciprocal specific (RSCA) combining ability as well as to predict the GCA, RGCA, SCA and RSCA effects. We also estimated the heterosis for each trait under LN and HN. The inheritance of root and shoot traits in tropical maize is largely modulated by additive gene action, but nonadditive gene action also plays a role in the inheritance of some traits; cytoplasmic genes also contribute a little to the inheritance of root size in tropical maize. LN stress has little influence on the inheritance of root traits, suggesting that the same breeding schemes might be used to improve the root size of tropical maize under both low-N stress and nonstress conditions. The lines VML016, VML022, VML033 and VML051 presented favorable nuclear genes, whereas the lines VML004, VML017, VML020, and VML028 presented favorable cytoplasmic genes for increasing root size in maize under both low-N stress and nonstress. Moreover, heterosis must also be explored in the development of tropical maize hybrids with enhanced root size, and the direction of the crosses must be considered in the exploration of heterosis for root size, especially under low-N stress environments.