The amount of hybrid seed produced in a female inbred block of maize (Zea mays L) can be limited by a number of factors including pollen load and shed duration. The objectives of this study were to determine if kernel number per ear in each row within the female block was limited by pollen density during silking or radiation received per plant after male inbred rows were removed. Three commercial hybrid seed production fields were used in this study. Pollen traps were placed strategically within the female block to evaluate pollen density during the shedding period. Intercepted photosynthetically active radiation (IPAR) was measured at several positions within the female block after the male inbred was removed from the field. Kernel number per ear was measured in each row two weeks after pollination and at harvest maturity. Total pollen deposition during the shedding did not vary across the four female rows. More PAR penetrated the canopy, however, in rows next to the open space formed by removing the male inbred. Kernel number per ear was similar in all four rows 15 days after pollination in all three fields. In two fields, however, kernel number per ear decreased 13% at physiological maturity for the inner two rows of the female block. The decrease in kernel number was correlated with less PAR at ear height (r2 = 0.97). These results indicate that variation in kernel number per ear across rows within the 4-row female block was not related to pollen amount. Rather, increased radiation interception per plant after male inbred removal limited kernel loss in the outer two rows of the female block. Typical growing conditions in hybrid seed production define an environment where source and sink limitations occur concurrently, the combination of genotype and growing condition will determine which limitation predominates.
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