Cercospora cf. nicotianae is a causal agent of Cercospora leaf blight of soybean

Cercospora leaf blight (CLB) of soybean was believed to be caused only by Cercospora kikuchii worldwide. However, recent studies that include molecular phylogenetic analyses reveal that several cryptic species within Cercospora are associated with the disease. In a previous study, following a survey of commercial soybean fields in Santa Cruz, Bolivia, Cercospora spp. strains were isolated and identified as Cercospora cf. nicotianae based on morphological characteristics and by sequencing parts of the calmodulin, histone H3, and translation elongation factor 1-alpha genes and placing into a multilocus phylogeny. In the present study, pathogenicity tests were carried out in greenhouse assays on eleven soybean varieties which confirmed the infection and reproduction of the symptoms originally observed in the field. All the inoculated varieties were infected and showed CLB symptoms. Isolates were recovered from all soybean varieties tested and monoconidial cultures resembled original inoculum, completing Koch's postulates. Thus, we confirm that according to the morphology of the conidia and cultures, pathogenicity tests, and molecular identification, C. cf. nicotianae is a causal agent of CLB of soybean.