The Relationship between Pollen Load and Fruit Maturation and the Effect of Pollen Load on Offspring Vigor in Cucurbita pepo
Abstract
In order to examine the relationships among the size of the pollen load, the number of seeds per fruit, the probability of fruit maturation, and offspring quality, we experimentally varied, by hand-pollinations, the number of pollen grains deposited onto stigmas of the common zucchini squash (Cucurbita pepo). We found that differences in the size of the pollen load (low, medium, and high) translate into significant differences in the number of seeds per fruit; moreover, fruits with high seed numbers are more likely to mature than fruits with medium or low seed numbers when the size of the pollen load is varied among flowers on an individual plant. In addition, a controlled greenhouse study revealed that offspring produced by high pollen loads germinate and emerge more rapidly and have more leaves, a greater stem circumference, and more dry biomass at 30 days after emergence than do offspring produced by low pollen loads. These studies indicate that progeny resulting from intense pollen-tube competition (high pollen loads) are more vigorous than progeny produced under conditions of little or no pollen competition (low pollen loads) and that zucchini can, as Lee (1984) hypothesized, improve the average quality of its seed crop by selectively aborting fruits on the basis of seed number.
