First report of southern blight of mung bean caused by Sclerotium rolfsii in China

Abstract Mung bean (Vigna radiata) is an important legume crop in China. An emerging mung bean disease with symptoms resembling southern blight was detected in China. This study was conducted to confirm and characterize the responsible pathogen through cultural and morphological characterization, and molecular detection using multiple specific primers and multiple-clone sequence analysis of the rDNA internal transcribed spacer (ITS) region and the translation elongation factor 1α (EF1α) and RNA polymerase II subunit 2 (RPB2) genes. All isolates obtained from mung bean were identified as Sclerotium rolfsii. Interestingly, we found that rDNA ITS, EF1α, and RPB2 sequences of all isolates consisted of two distinct types, which likely originated from different nuclei. Our findings indicated that S. rolfsii isolates were heterokaryotic and contain a heterozygous genome. Two trials of pathogenicity and host range revealed that all S. rolfsii isolates were not only strongly virulent to mung bean but also to several other important crops, indicating their potential threat to future agricultural production. To our knowledge, this is the first report of S. rolfsii causing southern blight on mung bean in China.