Poster Session: Biology of Pathogens - Mycology

361-P

Is Cercospora kikuchii the causal agent of Cercospora leaf blight and purple seed stain in the Gulf South? .
S. ALBU (1), P. P. Price (1), V. Doyle (2), R. Schneider (1)
(1) Louisiana State University Agricultural Center, Baton Rouge, LA, U.S.A.; (2) Louisiana State University, Baton Rouge, LA, U.S.A.

Cercospora kikuchii is considered to be the causal agent of Cercospora leaf blight (CLB) and purple seed stain (PSS), two economically important diseases of soybean (Glycine max) in the Gulf South. Identification of C. kikuchii is predominantly based on host association, cercosporin production and conidial morphology. However, these characters are unreliable for differentiating closely related species. Cercosporin production is variable among isolates, and it is difficult to induce sporulation in vitro. Recent molecular phylogenetic studies have shown that multiple cryptic species of Cercospora are capable of infecting a single host. Furthermore, previous studies determined that there is genetic diversity among cercosporoid soybean pathogens. Therefore, the etiology of CLB and PSS remains in question. In this study, we used a multilocus phylogenetic approach to determine if fungal isolates responsible for CLB and PSS are monophyletic. We addressed the utility of actin, calmodulin, elongation factor, histone and the internal transcribed spacer region for evaluating intraspecific relationships among Cercospora isolates collected from symptomatic soybean seeds and leaves. The multilocus phylogeny showed that none of the isolates collected in this study clustered within the clade containing the type strain of C. kikuchii. These results suggest that C. kikuchii is not the pathogen responsible for causing CLB and PSS in Louisiana and other gulf states.