Kernel set and flower synchrony within the ear of maize .1. Sowing date effects

Maize (Zen mays L.) grain yield depends on the number of kernels per plant that reach maturity. In this work, associations between floral development within the ear and final grain number of maize hybrids differing in prolificacy were studied under nonstress conditions in Argentina. In one experiment at Rojas (34 degrees 08'S), four hybrids were sown on four dates, at 8 plants m(-2), during 2 yr. Ears were observed at silking to determine the variation in the number of spikelets per ear. In the second experiment at Salto (34 degrees 33'S), a nonprolific (DK638) and a prolific (DK 3S41) hybrid were sown at 7 plants m(-2) on three dates. Ears were examined between the three-leaf stage and silking + 12 d to determine floral differentiation. No sowing date effect was evident for the number of spikelets per ear, the number of rows per ear, or the number of spikelets per row, but hybrids differed for these characters (P<0.05). During active spikelet initiation, spikelet number in apical ears increased at a rate of 0.13 (DK 638) or 0.17 (DK 3S41) spikelets per row per degrees Cd. At silking, almost all spikelets along a row in the apical ear had completed floral development in both hybrids, but the prolific type showed less spikelet abortion in the apical ear and a more synchronous development between ears. Kernel number per ear was independent of floral development stage at silking, but was related to the rate of ear growth (in length) around silking. These results suggest that assimilate partitioning to the ear during this period is critical for kernel set.