The effects of seed number and prior fruit dominance on the pattern of fruit production in Cucurbits pepo (Zucchini Squash)

Many plants, especially of species with indeterminate reproduction, show first-fruit dominance, in which the presence of developing fruit reduces future fruit maturation by increasing the abortion of later (younger) fruit and by inhibiting subsequent flower production. We examined the effects of seed number on first-fruit dominance by experimentally manipulating the number of pollen grains that were deposited onto stigmas of zucchini squash and then monitoring flower production, fruit growth, and fruit maturation. Our findings show (1) that fruits containing more seeds grow faster and achieve greater size; (2) that the presence of 6-15-d-old fruit significantly decreases the probability of female flower production while significantly increasing the probability of fruit abortion; (3) that the number of seeds in the prior developing fruit has a significant effect on the probability of flower production and fruit abortion, and (4) that when seed number varies among the fruits on a vine the fruit with the fewest seeds are the most likely to abort. It is concluded that the strength of dominance by a developing fruit depends on the number of seeds it contains and that this also influences the result of fruit to fruit competition.