Breeding studies on maize tolerance to low nitrogen fertilization

This study was meant to provide genetic information about selection among maize hybrids for NUE, and to evaluate the role of combining ability of inbred lines in hybrid performance under N- limited conditions.Results showed that:1)High tolerance and high response(HH),hybrids 7-5x12-3 and 7-5x145-1. 2)High tolerance and low response(HL), hybrids 100x224 and 421-2xSC-10. 3)Low tolerance and high response(LH), hybrids 32-3x308 and 308x290-3- 2.4)Low tolerance and low response(LL), hybrids 100x158 and 100x421-2. NUE at low N was significantly correlated with yield at high N. Grain yield was positively significantly correlated with chlorophyll concentration, ear diameter, biomass yield, kernel number/plant. Most of studied traits of hybrids showed larger heritability under low N than under high N. Direct selection for grain yield at low N was likely to be more efficient than indirect selection for grain yield at high N for improving grain yields under low N. Both GCA and SCA are equally important for genetic variability in performance of mean yield over N levels, but for grain yield and NUE at high N, GCA plays a greater role than SCA.