GENE EFFECTS CONTROLLING GRAIN YIELD AND NITROGEN USE EFFICIENCY TRAITS IN MAIZE

Selection of maize genotypes for N-use efficiency traits would lead to incorporation of high N efficiency in commercial hybrids. Field studies were conducted on plant N uptake in order to identify genotype differences in N-use efficiency and its relationship to grain yield, and determine the magnitude of additive, dominance and epistatic gene effects. Generations developed from nine inbred lines were tested in four N-level environments. Efficiency of N utilization was evaluated by the ratios of total plant dry matter (TDM) and grain dry matter (GDM) to total N yield (TNY). Harvest index (HI) and nitrogen harvest index (NHI) were evaluated by using ratios of GDM to TDM and grain nitrogen yield to TNY, respectively. Least square methods were used to obtain estimates of genetic parameters. Dominance gene effects (h(,jj(,\u27))) made the major contribution to variation in most of the traits. Partitioning of the h(,jj(,\u27)) effects reveals that average heterosis was the most important effect. Additive effects were significant for most traits, but the magnitude of those effects relative to dominance and epistatic effects were less important in the inheritance of those traits. Additive x additive epistatic effects were important in environments with less N stress. The magnitudes of the epistatic parameters indicate that epistatic gene effects are operating in grain yield, NHI and N utilization efficiency. Identification of efficient genotypes will provide opportunities to plant breeders for utilizing them in breeding for N-use efficiency necessary to achieve maximum and efficient crop production. Rapid advance in breeding for N-use efficiency can best be done using procedures which emphasize dominance, but additive and epistatic gene effects should also be considered. Dominance and additive x additive epistasis can be utilized in intrapopulation selection schemes; but overdominance and dominance types of epistasis require some form of reciprocal recurrent selection, which requires that two heterotic populations be maintained so that inbred lines can be extracted from each to evaluate in interpopulation hybrids. Improvement of the source populations might be done with S(,2) family testing and selection after screening among S(,1) families, or by some other system such as RRS using full-sib families