APS Abstract of Presentation

Prevalence of frogeye leaf spot caused by Cercospora sojina in Ohio
C. CRUZ (1), A. E. Dorrance (1)
(1) The Ohio State University, OARDC, Wooster, OH
Phytopathology 98:S43

The severity and prevalence of frogeye leaf spot (FLS), a common disease of soybean in the southern U.S., has increased in Ohio during the previous 3 years. The objectives of this study were to determine: 1) if seed or soybean residue is the primary source of inoculum in the spring; and 2) if there is a shift in optimum temperature for growth of C. sojina. Soybean seed harvested from infected plants during 2006 were planted. Flats with 75 seed each were placed under mist for 30 days or in a greenhouse and watered twice per day. No leaf spots of C. sojina developed on any of the seedlings. In October 2007 stems and leaves with FLS were placed on the soil surface at two locations in Ohio. Conidia of C. sojina were detected from these stems and leaves recovered on January 2008. Fifty C. sojina isolates collected from 22 Ohio counties were compared to an isolate from southern Illinois. Mycelial growth at 17, 21, 25, 28, and 32°C was measured 6, 14, 22, and 30 days after plating in 2 separate experiments. There were significant differences in mycelial growth among the isolates after 30 days. These preliminary results indicate that isolates have a wide range of optimum temperatures and that this fungus may be overwintering on soybean residue in Ohio.

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