Phomopsis seed decay of soybean (Glycine max L.) is endemic in the United States, but new fungi are involved

Authors: PETROVIC, KRISTINA - South Dakota State University; SKALTSAS, DEMETRA - Orise Fellow; Castlebury, Lisa; KONTZ, BRIAN - South Dakota State University; ALLEN, TOM - Mississippi State University; CHILVERS, MARTIN - Michigan State University; GREGORY, NANCY - University Of Delaware; KELLY, HEATHER - University Of Tennessee; KOEHLER, ALYSSA - University Of Delaware; KLECZEWSKI, NATHAN - University Of Illinois; MUELLER, DAREN - Iowa State University; PRICE, PAUL - Louisiana State University; SMITH, DAMON - University Of Wisconsin; MATHEW, FEBINA - South Dakota State University

Submitted to: Plant Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/17/2020
Publication Date: 5/5/2021
Citation: Petrovic, K., Skaltsas, D.N., Castlebury, L.A., Kontz, B., Allen, T.W., Chilvers, M.I., Gregory, N., Kelly, H., Koehler, A.M., Kleczewski, N., Mueller, D.S., Price, P.P., Smith, D.L., Mathew, F.M. 2021. Phomopsis seed decay of soybean (Glycine max L.) is endemic in the United States, but new fungi are involved. Plant Disease. https://doi.org/10.1094/PDIS-03-20-0604-RE.
DOI: https://doi.org/10.1094/PDIS-03-20-0604-RE

Interpretive Summary: Fungi in the genus Diaporthe occur on many different plant hosts with some species causing disease and other co-existing with their host plants without causing disease. Because many species in this genus have similar microscopic appearances, they are often difficult to identify correctly. In this study, 10 species of Diaporthe were isolated from soybean seed from soybean-growing areas all over the United States and characterized using DNA sequences and cultural characteristics. Three new species were discovered and several species not formerly associated with soybeans were found. This research will be used by extension agents, plant breeders, plant pathologists, and plant quarantine officials to implement management strategies and to accurately determine the presence of these species in the United States and other countries to keep American agriculture safe.

Technical Abstract: Phomopsis seed decay is a major disease of soybean (Glycine max L.) in the U.S. In this study, 45 isolates of Diaporthe were recovered from seeds sampled from soybean fields affected by Phomopsis seed decay in eight U.S. states. These isolates were identified to belonging to 10 species of Diaporthe based on morphology and phylogenetic analyses of the internal transcribed spacer, the partial translation elongation factor 1-alpha and beta-tubulin genes. Of the 10 species, D. longicolla was commonly recovered; D. bacillus, D. flavescens and D. insulae were novel; D. kongii, D. ueckerae, and D. unshiuensis were detected for the first time on soybean in the U.S. One representative isolate of the 10 species was examined for pathogenicity on seeds of cv. ‘Sava’ under controlled conditions. Seven days post-inoculation, the incidence of D. aspalathi, D. bacillus, D. longicolla, D. sojae, D. ueckerae, and D. unshiuensis in seed was 100%. The incidence of D. kongii, D. caulivora, D. flavescens and D. insulae in seed was 97%, 88%, 79%, and 79% respectively. This study suggests that the species diversity of Diaporthe causing Phomopsis seed decay in the U.S. may have changed and further investigation on the infection process of these pathogens is warranted.