Pre-inoculation by an arbuscular mycorrhizal fungus enhances male reproductive output of Cucurbita foetidissima

Male and female reproductive output of Cucurbita foetidissima, a gynodioecious native perennial, was examined in a 2-yr greenhouse/outplanting study. Plants were divided into three treatment groups: (1) a low-phosphorus (P) soil mix control; (2) a low-P soil mix with the addition of mycorrhizal inoculum (Glomus intraradices); and (3) a high-P soil mix. Plants were outplanted after one summer of greenhouse growth and harvested in the fall of the second year. High-P treatment plants grew best during the first year, having significantly longer vines than either low-P treatment. By the end of the second year, however, treatment had no significant effect on either aboveground biomass or weight of the tuberous storage root. Tissue concentrations of N and P also did not differ significantly with treatment. Male reproductive output was significantly enhanced by the addition of mycorrhizal inoculum, resulting in a threefold increase over control plants in the production of male flowers. In contrast, treatment had no significant effect on aspects of female reproductive output, including number of female flowers, percent fruit set, total fruit biomass produced by the plant, or mean fruit weight. Fruit production was correlated with vegetative aboveground biomass and is likely reflective of carbon status. These results suggest that mycorrhizal colonization may differentially influence male and female components of plant reproduction.