Poster Session # 20: Predator - Prey / Mutualism - Parasitism Ecology.

Thursday, August 7 Presentation from 5:00 PM to 6:30 PM. SITCC Exhibit Hall B.

Effects of the pathogen Uromyces ari-triphylli on reproductive biology and growing season of Arisaema triphyllum.

Cook, Jessica*,1, 1 Michigan State University, East Lansing, MI

ABSTRACT- Arisaema triphyllum, Jack-in-the-pulpit, is a common spring ephemeral in eastern forests of North America. Populations frequently contain plants infected with the systemic rust Uromyces ari-triphylli. Previous research demonstrated that disease reduces seed set in infected females, but results came from a single A. triphyllum population over a single growing season. In this study, I do a detailed comparison of flowering phenology, female reproductive success, and length of growing period for healthy and infected plants at four sites in Michigan. Light intensity, soil pH, soil moisture were also measured to determine their influence on growth and flowering. Hand pollination experiments were conducted to determine if reduced seed set is caused by lower pollinator visitation of diseased plants. Environmental variables did not affect flowering period, emergence date, and growth period of healthy or diseased plants, while disease influenced growing period and flowering phenology. Diseased plants emerged significantly earlier (on average five days) than healthy plants. Growing season length was significantly shorter for diseased plants (average 41 days infected, 57 days healthy). Average flowering period for healthy plants (28 days) was significantly longer than diseased plants (23 days). The percentage of healthy females setting seed (71%) was also significantly higher than diseased females (17%). Hand pollination increased seed set in both healthy (34%) and diseased females (133%). Healthy and diseased plants did not differ in pollen viability. For females that produced seed, differences in the number of seeds produced were only slightly significant. This pathogen exerts a strong influence on the life history of A. triphyllum by limiting flowering time, growing season, seed production, and resource allocation to developing seeds. At the population level, this pathogen can dramatically reduce individual plant growth and fitness, which can affect A. triphyllum population dynamics both genetically and numerically.

Key words: Arisaema triphyllum, pathogen, flowering period, reproductive success