Limiting temperatures for urediniospore germination are low in a systemic rust fungus of tallgrass prairie

Potential responses of plant disease phenology to climate change have been addressed primarily in agricultural systems. As a first step toward understanding the phenology of Uropyxis petalostemonis, a rust fungus commonly infecting the legume Dalea candida in U.S.A. tallgrass prairie, we evaluated the effects of temperature on urediniospore germination. While urediniospore germination for many rust fungi has been reported to decline only when temperatures are well above 25 degrees C, in vitro germination of U. petalostemonis dropped sharply at this temperature. Responses observed on water agar, potato dextrose agar and lima bean agar were similar, although lima bean agar supported a higher percentage germination overall. The low limiting temperatures suggest that most epidemically important new infections by U. petalostemonis occur in spring. High summer temperatures in tallgrass prairie might push infection by this rust fungus species to earlier in the year and select for stronger systemic growth characteristics.