Resource Re-Allocation Following Fruit Removal in Cucurbits: Patterns in Two Varieties of Squash

The effects of removal of marketable-sized fruits on investment toward male, female and vegetative activities were evaluated using two monoecious varieties of cultivated squash, Cucurbita pepo, cv. Striato d'Italia o di Napoli, and cv. Zucchini Black. Leaf and flower demography were used to examine potential trade-offs among these activities. Treated individuals produced more leaves, but individual leaf life expectancies were lower than those of controls. Fruit removal also significantly stimulated the production of male and female flowers, fruit and total above-ground biomass. By contrast, permitting the extended process of fruit maturation in controls significantly decreased the overall production of both male and female flowers. There was no significant difference in total fruit mass between treated and control individuals. However, production of female and male flowers was labile, and responsive to the resource relationships operating within the plant. Treated plants produced more female (potentially fruit-bearing) flowers as their fruits were harvested, and both groups of plants produced more male flowers at the end of the season. Overall, the squash cultivar produced almost twice as many male flowers as the zucchini cultivar; the harvesting treatment enhanced male flower production later in the season, and did so earlier in squash than in zucchini. Since reduced fruit production is achieved through reduced production of female flowers rather than through abortion of early fruits, and this precedes the period where resource limitation is anticipated, it is concluded that available resources do not directly prevent fruit development. The results are interpreted in the light of recent artificial selection for one to two large fruits per plant in the case of the squash cultivar, and many smaller fruits in the case of the zucchini.