Characterization and Survival of Cercospora sojina in Ohio

Frogeye leaf spot (FLS) of soybean, caused by Cercospora sojina, has increased in incidence and severity during the last 3 years in Ohio and caused substantial economic losses for the first time during 2006. FLS is common in the southern United States but has only recently been reported to cause losses in the north-central region. This study evaluated several traits of the fungus which may have contributed to the increase in disease incidence such as: the ability of C. sojina to overwinter and sporulate on infested soybean debris; optimum temperatures for mycelial growth; races (pathotypes) present in Ohio; and pathogenicity on cultivars with Rcs gene(s) for FLS resistance. Conidia of C. sojina were recovered from soybean debris collected at two locations from December to May 2007-2008. The optimum temperature for mycelial growth of all isolates evaluated in this study including those from Louisiana and southern Illinois was 25°C. The 50 isolates of C. sojina collected in Ohio were able to infect a mean of 4.9 of 12 differentials and had a total of 20 different pathotypes. The Rcs 3 gene conferred resistance to all of the Ohio isolates. Survival of C. sojina in the field during the winters of 2005 to 2007 contributed to the increase of C. sojina during the 2005, 2006, and 2007 production seasons in Ohio. Accepted for publication 11 April 2009. Published 12 May 2009.