Occurrence of collar rot caused by Athelia rolfsii on soybean in China

Soybean (Glycine max) is an annual leguminous plant that has been cultivated in China for over 4500 years. During a survey conducted in 2018, collar rot was observed in soybean crops in Zhangzhou, Fujian Province, China. The disease first appeared as water-soaked lesions on the surface of the stems, followed by the development of large decayed areas with abundant white mycelium. A fungus was isolated from the diseased stems, which grew to form white colonies within 3 days of incubation on potato dextrose agar. Subsequently, white sclerotia began to form, which eventually turned yellow and then dark brown. Pathogenicity tests were performed on healthy soybeans and collar rot symptoms developed 6-8 days after inoculation. Sequencing of PCR products amplified with the primers ITS1 and ITS4 indicated 99% identity with a reference sequence of Athelia rolfsii (JN081867.1) in the GenBank database. Based on morphological and molecular characteristics, the fungal pathogen was identified as Athelia rolfsii (anamorph: Sclerotium rolfsii). Athelia rolfsii infects many economically important crops and attention should be given to other potentially susceptible hosts in the region.