Synchronous pollination within and between ears improves kernel set in maize

In maize (Zea mays L.), the later-fertilized ovaries often abort, thereby reducing kernel set. We examined whether altering the time interval between pollination of florets within an ear or between ears could affect final kernel number per plant. Synchrony of pollination was varied by natural- and hand-pollination of four hybrids, contrasting in prolificacy (ears plant(-1)). Plants were grown in the field at low (2.5 and 3 plants m(-2)) and high (7.5 and 9 plants m(-2)) plant populations, without water or nutrient stress. Increasing plant population generally delayed silk appearance, but most silks were exposed within 5 d after silking (DAS). Synchronous pollination of all exposed silks on apical and sub-apical ears 5 DAS improved kernel number (KN) per plant and the floret fertility index (FFI = number of kernels/ number of pollinated silks), relative to open-pollinated plants. At low plant populations, the KN plant(-1) increase resulted primarily from a large increase (39-535%, depending upon the hybrid) in kernels on sub-apical ears. At high plant populations, only apical ears set kernels. Synchronous pollination increased KN in these ears 8 to 31%, depending on the hybrid. Thus, timing of pollination had a large impact on kernel set, and the disadvantage associated with an ontogenetic delay in silk emergence could be partially overcome by synchronous pollination. Because delayed pollination of early-silking ovaries allowed a greater number of the late-silking ones to set kernels, factors other than assimilate availability per fertile floret likely are involved in controlling kernel set.