Genetic diversity of Cercospora sojina revealed by amplified fragment length polymorphism markers

Cercospora sojina Hara, the causal agent of frogeye leaf spot of soybean (Glycine max (L.) Merr.), causes yield reductions worldwide. Although the phenotypic diversity (physiological races) of this pathogen has been assessed through its ability to affect soybean lines with different resistant genes (Rcs genes), little is known about the pathogen's genetic diversity. In order to better understand the genetic diversity that exists with C. sojina, a historical collection of 62 C. sojina isolates from Brazil (10 isolates), China (7 isolates), Nigeria (1 isolate), and United States (44 isolates) was used for genetic diversity analysis with amplified fragment length polymorphism (AFLP) markers. The average genetic similarity of the isolates was 0.56 on a scale between 0 and 1, indicating a high degree of genetic diversity within the species. Cluster analysis resulted in two major clusters and seven sub-clusters. Two isolates collected from Georgia were clustered together, and two isolates from China were clustered together. Besides these four isolates, no clear separation of isolates based on origin was found. Our results provide evidence that substantial genetic diversity exists within the species of C. sojina and that selection for broad-spectrum host-resistance should be targeted in soybean breeding programmes.