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 b y adjusting the relative investment of resources in growth and reproduction , through the male or female function, in response to alterations in resour ce availability throughout the growing season. Fruit production has been sh own to be costly to plants in terms of carbon and mineral nutrients that, o therwise, could be used for further growth, defense, or pollen production a nd dispersal. Consequently, the failure of flowers to initiate and/or produ ce mature fruits (e.g., because lack of pollination or flower predation) sh ould free resources for growth, defense, and additional flower production. This prediction, however, assumes that plants have the physiological mechan isms to appropriately reallocate unused resources from the female function. This study examines whether plants of Cucurbita pepo ssp. texana reallocat e resources from fruit/seed production to growth and flower production in r esponse to the removal of pistillate flowers 1 d after anthesis. This wild gourd is an annual, monoecious vine that produces a single flower per repro ductive node. We found that when plants were not permitted to allocate reso urces to fruit and seed production, the vines grew faster, initiated more s taminate and pistillate flower buds, and produced more pistillate flowers b ut had a smaller proportion of staminate buds that reached anthesis and few er staminate flowers on their main shoot than plants with fruit/seed produc tion. These findings indicate that the resources that would have gone into fruit maturation were reallocated to growth and flower bud production. Howe ver, 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 flowe r buds to develop to anthesis results from an increase in the hormonal sign al (ethylene) that stimulates pistillate flower development on vines withou t developing fruits.