Growth and resource allocation in Cucurbita pepo ssp. texana: Effects of fruit removal

Recent theory indicates that plants may be able to increase their fitness by adjusting the relative investment of resources in growth and reproduction, through the male or female function, in response to alterations in resource availability throughout the growing season. Fruit production has been shown to be costly to plants in terms of carbon and mineral nutrients that, otherwise, could be used for further growth, defense, or pollen production and dispersal. Consequently, the failure of flowers to initiate and/or produce mature fruits (e.g., because lack of pollination or flower predation) should free resources for growth, defense, and additional flower production. This prediction, however, assumes that plants have the physiological mechanisms to appropriately reallocate unused resources from the female function. This study examines whether plants of Cucurbita pepo ssp. texana reallocate resources from fruit/seed production to growth and flower production in response to the removal of pistillate flowers 1 d after anthesis. This wild gourd is an annual, monoecious vine that produces a single flower per reproductive node. We found that when plants were not permitted to allocate resources to fruit and seed production, the vines grew faster, initiated more staminate and pistillate flower buds, and produced more pistillate flowers but had a smaller proportion of staminate buds that reached anthesis and fewer staminate flowers on their main shoot than plants with fruit/seed production. These findings indicate that the resources that would have gone into fruit maturation were reallocated to growth and flower bud production. However, despite an increased investment in the production of staminate flower buds, a relative surplus of resources did not result in an increase in the production of staminate flowers. Recent findings concerning the physiology of sex expression in Cucurbita indicate that the failure of staminate flower buds to develop to anthesis results from an increase in the hormonal signal (ethylene) that stimulates pistillate flower development on vines without developing fruits.