Quantitative Relationships between Pollen Shed Density and Grain Yield in Maize

Abstract

Pollen production generally is not considered a limiting factor in modern maize (Zea mays L.) production. In some modern hybrids, however, smaller tassel size, use of male sterile blends, and top cross production may limit pollen availability. This study was conducted to establish the lower limits for pollen production needed to ensure maximum kernel set, and to devise a method for predicting pollen production from simple measures of tassel development. Isolated blocks of male fertile plants were established in a field of male sterile plants. The level of male fertility was varied from 0 to 100% by detasselling (Pioneer 3978) or by using mixtures of male fertile and male sterile isolines (Pioneer 3925 and 3925S). Pollen shed was measured daily with passive pollen traps. A Population Index, derived from the percentage of plants shedding pollen and the average pollen production per plant, accurately predicted the seasonal pattern and total pollen shed for each male fertility treatment. Hybrids used in this study shed pollen for 10 to 12 d, with a peak intensity 2 to 3 d after anthesis (50% plants shedding pollen). Individual tassels produced 4.5 × 106 pollen grains on average, and shed pollen for 5 or 6 d. Variation in grain yield across male fertility treatments was closely correlated to kernels per plant (r2 = 0.998). Seasonal pollen production limited kernels per plant at pollen densities less than 3000 pollen grains silk−1 This lower limit for effective kernel set occurred at male fertility levels less than 50% for both hybrids. Grain yield, however, was maintained at male fertility levels as low as 20% because of compensation in grain size. These results demonstrate that a minimum pollen shed density per exposed silk is required to achieve maximum kernel set and grain yield. They also show that the seasonal pattern of pollen shed can be predicted from simple measures of staminate flower development. Together, these results provide a rational basis for achieving high kernel set under field conditions in which pollen production might be limiting.