Diaporthe species associated with symptomatic and asymptomatic infection of soybean stems in Minnesota: identity, virulence, and growth characteristics

Stem diseases of soybean with symptoms typical of infection by Diaporthe spp. are common in the Northern USA. Information is limited, however, on the characteristics of the associated pathogens. This study determined the identity and characteristics of Diaporthe spp. associated with symptomatic and asymptomatic soybean stems across diverse environments in Minnesota. Plants with symptoms of stem canker, pod and stem blight, and plant dieback, as well as asymptomatic plants, were sampled. Agar-based media and PCR assays were used to isolate and detect Diaporthe spp. from stems. The isolates were identified to species based on DNA sequencing and morphology. Diaporthe spp. were common in symptomatic and asymptomatic plants across all environments. Three species were detected: D. longicolla, D. caulivora, and D. cucurbitae. Diaporthe longicolla was the most widespread in distribution. Diaporthe cucurbitae was isolated from symptomatic soybean and confirmed to be a soybean pathogen for the first time. Only D. longicolla was detected in asymptomatic plants. While all isolates were pathogenic to soybean, virulence differed among isolates, and cultivars differed in susceptibility. Temperatures of 25°C and 32°C differentially influenced the growth of D. longicolla and D. caulivora. All isolates were sensitive to pyraclostrobin and tebuconazol. The results advance our understanding of the Diaporthe species associated with different soybean stem diseases, as well as their characteristics and management.