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Oral: Oomycete Biology


Temperature and light effects on germination of Peronospora effusa
R. CHOUDHURY (1), S. Koike (2), N. McRoberts (1) (1) University of California, Davis, U.S.A.; (2) UCCE Monterey County, U.S.A.

Spinach downy mildew, caused by the biotrophic oomycete Peronospora effusa, is an economically important disease that is found in all spinach growing regions of the US. To effectively predict disease risk we need to understand the response of P. effusa to different environmental conditions. However, compared with several other downy mildew pathogens, relatively little research has been done on the optimal environmental conditions for growth and sporulation of P.effusa. We conducted several germination assays, exposing P. effusa sporangia to different temperature and lighting conditions. Between 5 and 25°C under constant darkness, germination of P. effusa sporangia on water agar declined following an approximately logistic decay. These results were qualitatively different from a previous study of P. effusa germination that found a bimodal response curve, with increased germination at lower and higher temperatures. Time course studies revealed that most sporangia germinated within the first eight hours of plating, regardless of incubation temperature. Sporangia exposed to green or blue light had significantly reduced germination when compared with those exposed to red, yellow, or no light. Light intensity and color significantly impacted germination, although the effect of color varied by light intensity. The use of these results in the development of a disease risk model will be discussed.