GENOTYPIC VARIATION FOR NITROGEN UPTAKE BY MAIZE KERNELS GROWN IN-VITRO

The role of N in controlling kernel growth of maize (Zea mays L.) is difficult to determine at the whole plant level, especially with regard to genotypic differences. The in vitro kernel culture technique can be used to investigate this problem because it minimizes environmental and maternal influences during grain fill. Therefore, the objective of this study was to characterize genotypic variation in the growth and N content and concentration of in vitro cultured kernels in response to varying N supply. Kernels of eight single-cross hybrids and four inbreds mere grown to maturity in vitro on media containing 0 to 50 mM N and analyzed for dry weight and N composition. Distinct differences in the level of N required to achieve maximum kernel weight were observed for both hybrids and inbreds with the optimum external concentration ranging from 10 to 50 mM. For all genotypes, the pattern of kernel N accumulation in response to N supply was relatively similar, and the N concentrations required to obtain maximum kernel N were greater than those needed for maximum dry weight. Although kernel N concentration increased with increases in N supply, the relative genotypic rankings were similar except at the lowest levels of medium N. These findings indicate that maize genotypes differ in the level of N needed to achieve maximum kernel weight in vitro, which may be due to differences in how kernels utilize N for starch deposition and growth.