Phylogenetic diversity of Calonectria ilicicola causing Cylindrocladium black rot of peanut and red crown rot of soybean in southern China

Calonectria ilicicola Boedijin & Reitsma (anamorph: Cylindrocladium parasiticum Crous, Wingfield & Alfennas) is an important pathogen worldwide, which causes Cylindrocladium black rot (CBR) in peanut (Arachis hypogaea L.) and red crown rot (RCR) in soybean [Glycine max (L.) Merr.]. We isolated the CBR and RCR pathogens from heavily diseased peanut and soybean fields in southern China and assessed their pathogenicity. Two inoculation methods were applied separately to evaluate the pathogenicity of different C. ilicicola strains on peanut cultivar Yueyou 13. Our results indicate that the Chinese C. ilicicola strains exhibited a range of virulence on peanut, with strains of soybean origin exhibiting a weak virulence relative to strains isolated from peanut. Multilocus sequence type analysis indicates that the C. ilicicola strains partitioned into two distinct clades, which were heavily structured based on geographical origin. Phylogenetic results demonstrated that the origins of C. ilicicola in southern China were multiple. This study also revealed that the backgrounds of CBR pathogens may be different from those of RCR pathogens.