Identification of Cercospora species associated with Cercospora Leaf Blight of soybean in Brazil

Diseases of soybean caused by Cercospora spp. are endemic globally throughout the soybean production regions. Research into the genus Cercospora in soybean has historically been underrepresented in terms of species diversity due to a dependence of differentiation on morphological characteristics, symptomology, and host associations. Previous studies have indicated two species, C. kikuchii and C. sojina, to be infective on soybeans. However, recent research, including molecular analytical methods, has shown that a broader range of species can be associated with the disease. Therefore, the objective of this study was to identify the predominant species of Cercospora associated with Cercospora Leaf Blight (CLB) in soybean in Brazil and to investigate the pathogenicity of the identified species in greenhouse experiments. For this purpose, 43 isolates of Cercospora spp. from Brazil were analyzed using a multi-locus phylogenetic approach with five different loci from the gDNA. Furthermore, cloning was performed on 11 leaf samples to correctly identify the species present. Of the 43 isolates, 41 were identified as Cercospora sp. Q, one as C. kikuchii and one as C. cf. sigesbeckiae. In all the 11 cloned leaf samples, C. sp. Q was the predominant species. However, C. kikuchii, C. cf. flagellaris, C. cf. nicotianae and C. sp. P were also detected in many samples, although at much lower frequencies. Furthermore, infection of soybean plants under greenhouse conditions was achieved for the predominant species (C. sp. Q). This study proves the pathogenicity of Cercospora sp. Q on soybeans, suggests that C. sp. Q is the most frequent species of Cercospora infecting the analyzed soybean samples in Brazil and confirms that the CLB can involve more than one species of Cercospora simultaneously. However, further studies are required to identify and establish improved markers for the molecular differentiation between Cercospora species.