Phomopsis longicolla β conidia in naturally infected soybean

Abstract

P. longicolla is primarily known as a soybean seedborne pathogen but it can be isolated from all parts of the plant. Atypical symptoms have been frequently noted on the basal parts of soybean stems of mature plants: slightly sunken lesions with irregular shapes and sizes, bordered by a thin black margin with diffusely distributed pycnidia with α and β conidia. Initially, it was believed that the causal agent was the fungus P. sojae, however morphological characteristics of the isolates suggested that the causal agent was not P. sojae. This study was an attempt to prove that, under certain conditions, P. longicolla produces masses of β conidia. Beta conidia were observed for quite some time in the field, but they were believed to belong to P. sojae, which typically forms this type of conidia. However, after isolation from infected plant parts, the fungus formed colonies and reproductive organs which were identical to the morphological characteristics of P. longicolla described by Hobbs et al. (1985). In other words, we found evidence that the isolated fungus was P. longicolla.