An Emerging Disease of Leaf Spot Caused by Paramyrothecium vignicola on Soybean in China.

Soybean (Glycine max) is an important legume crop worldwide. An emerging leaf spot was observed in soybean plants with obvious black necrotic spot symptoms during the disease survey in Changping District, Beijing, China. To confirm the causal agent, the pathogen was isolated from the diseased leaves. Three isolates were obtained and showed a morphology extremely similar to Paramyrothecium vignicola. The isolates were identified by morphological and molecular characteristics. Phylogenetic analyses were performed using multiple gene regions (ITS, cmdA, rpb2, and tub2). The result indicated that the three isolates showed a high similarity (100%) with the known P. vignicola strains. Pathogenicity and host range tests of the isolates were performed on soybean and other legume crops. Three isolates were strongly pathogenic to soybean, hyacinth bean, common bean, faba bean, pea, mung bean, and lentil; moderate pathogenicity on adzuki bean; mild pathogenicity on cowpea and peanut. To screen resistant germplasms for disease control, the screening experiment of inoculum concentration of P. vignicola were performed. The result showed the most suitable concentration of P. vignicola isolate is 1 × 105 spores/mL for evaluation of germplasms resistance. Paramyrothecium species have been frequently identified to cause leaf spot and blight disease on a wide range of vegetables, ornamental plants, and economic crops. To our knowledge, this is the first report of P. vignicolaa inducing leaf spot on soybean worldwide. This study indicates P. vignicola might pose a potential risk to legume crops in the future.