FLORAL ASYNCHRONY AND KERNEL SET IN MAIZE QUANTIFIED BY IMAGE-ANALYSIS

A delay in the onset of silk emergence relative to pollen shed often decreases kernel set in maize (Zea mays L.). Lack of pollen, failure of silks to emerge, and loss of silk receptivity all are probable causes for kernel loss. To date, it has not been possible to distinguish between these possibilities, due to the lack of quantitative information on the intensity of pollen shed and progress of silk emergence under field conditions. Using a computer-aided image analysis system, we measured the daily progress of silk emergence and the intensity of pollen shed in the field. Kernel set also was measured on plants whose silk emergence varied from 8 d before to 13 d after anthesis (DAA). About 200 silks emerged on the first day silks appeared and >90% of the florets had silks exposed within 3 d. Pollen shed followed a normal distribution with time, peaked 3 DAA, and ended 13 DAA. On ears with silks exposed to pollen for only one d, nearly all florets set kernels when pollen was shed at intensities greater than almost-equal-to 100 grains cm-2 d-1; however, percent set in apical floret positions decreased when the onset of silk emergence was delayed > 3 DAA, despite pollen shed at a rate sufficient to ensure high kernel set. These results indicate that asynchrony between silk emergence and pollen shed decreases kernel set because silks emerge after pollen amount becomes limiting. In the current experiment, the intensity of pollen shed limited kernel set only beyond 7 DAA. Also, silks emerged prior to anthesis remained receptive to pollen for at least 5 d. This finding suggests that selection for silk emergence prior to pollen shed (protogyny) may improve kernel set in maize under conditions known to delay silk emergence.