Frogeye leaf spot caused by Cercospora sojina: A review

Frogeye leaf spot (FLS), caused by Cercospora sojina, is an economically important disease of soybean in many parts of the world where soybean is grown, including the United States and Argentina. Yield losses caused by FLS epidemics are mainly due to reduced photosynthetic leaf area, premature defoliation and reduced seed weight. Epidemics may be initiated from inoculum produced on infected plant residue where the pathogen can overwinter for up to two years. Many questions relating to population biology, genetic variability and pathotype structure remain unanswered. Race designations for C. sojina are under debate since the use of the 12 soybean differentials has produced inconsistent numbers of races in separate studies. Although a sexual stage for C. sojina has not been observed in either field or laboratory conditions, equal proportion of mating-type loci and high genotypic diversity suggest that populations of C. sojina are most likely to be undergoing cryptic sexual reproduction. Management practices for this disease include the use of cultivars with partial or complete resistance (Rcs genes), cultural practices (crop rotation and tillage) and foliar fungicide applications. However, resistance to quinone outside inhibitor (QoI) fungicides (caused by the G143A mutation in the Cytochrome b gene) has been reported since 2010, and resistant populations have become widespread across more than 20 soybean-producing states in the U.S. This review provides detailed information on the taxonomy, identification and genetic diversity of the pathogen. It also summarizes epidemiological aspects and strategies to combat this increasing threat to soybean crops worldwide.