The influence of herbivory on measures of male function in Cucurbita pepo ssp. texana.
Winsor, James*,1, Smith, Matthew 2, Stephenson, Andrew2, 1 The Pennsylvania State University, Altoona2 The Pennsylvania State University, University Park
ABSTRACT- Compared to their effects on fruit and seed production, the effects of plant disease on fitness through the male function are less well known. We examined the interaction of herbivory and disease transmission on male function in garden-grown Cucubita pepo ssp. texana. This wild gourd is susceptible to infection by several common viral diseases of cucubits, which are vectored by spotted and striped cucumber beetles (Diabrotica and Acalymma respectively). Sixty plants from each of five maternal families were transplanted as seedlings into experimental gardens. Half of the plants were randomly selected for weekly application of Asana XL, a contact insecticide used for beetle control; the remaining plants were sprayed with comparable amount of tap water. Damage by beetles and infection by viruses were assessed three times during the growing system by a 0 to 5 scale. Reproductive output through the male function was measured by (1) number of staminate flowers produced, (2) mean pollen grains per flower, (3) pollen tube growth rate in vitro, and (4) pollen success in siring seeds in vivo. Sprayed plants were significantly less likely to be damaged by beetles than nonsprayed plants (1.2 vs. 2.9 on the 5 point scale) and were significantly less likely to be infested by viruses (0.66 vs. 0.79 on the 5 point scale). Sprayed plants produced significantly more staminate flowers (32%), significantly more pollen per flower (6%), and significantly faster pollen tube growth in vitro (11%). Moreover, the pollen from sprayed plants was more successful than that of nonsprayed plants in competition with zucchini pollen on zucchini maternal parents. These data show that plant fitness, measured through the male function, is enhanced when disease-carrying vectors are controlled.
Key words: herbivory, disease, male function, cucurbita
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