Diversity of Pythium Species Associated with Snap Bean Production in Delaware

• Yuki Jatmiko, Plant Science, University of Maryland Eastern Shore

• Alyssa Koehler, Plant and Soil Sciences, University of Delaware

Snap beans are an important processing vegetable crop in Delaware and the occurrence of Pythium cottony leak has increased in recent seasons. Pythium is a pathogenic oomycete that thrives in wet conditions and poorly drained fields, resulting in root rot, stem lesions, and pod infections in snap beans throughout the growing season. White cottony growth on infected beans reduces yield, can result in rejection of the crop, or can present issues in post-harvest storage. While multiple organisms can be associated with cottony leak symptoms, no isolate characterization studies have been conducted in Delaware. In order to determine which species may be involved, a survey was initiated in summer 2023 to collect symptomatic snap beans from multiple fields. After collection, samples were brought back to the lab and pure culture isolates were obtained using selective media.  Hyphae from each representative culture were used for DNA amplification with Phire Plant Direct Master Mix for Polymerase Chain Reaction (PCR) amplification of the internal transcribed spacers (ITS45) region. PCR products were sent for sequencing and two species, Pythium aphanidermatum and Pythium ultimum, were identified.  Understanding species diversity provides critical information to monitor and track how Pythium species interact with the snap beans in the field in the long run. This study will aid future research to determine if planting date or variety selection could be used as tools to mitigate snap bean yield loss from Pythium.