P-539 - Differences in QoI fungicide sensitivity of Colletotrichum orbiculare in the eastern United States based on cucurbit host of origin

Monday, August 4, 2025

4:30 PM - 5:15 PM HST

Location: Exhibit Hall 3

Presenting Author(s)

RP

Rashmi Pokhrel (she/her/hers)

Graduate Reseach Assistant
Department of Plant Pathology, University of Georgia, Athens
Athens, Georgia, United States

Author(s)

NK

Navjot Kaur, PhD

Postdoctoral Associate Ad
Department of Plant pathology, University of Georgia, Tifton
Tifton, Georgia, United States
CC

Chloe Dela Cerna

Graduate Research Assistant
Institute of Plant Breeding, Genetics and Genomics (IPBGG), University of Georgia, Athens
Athens, Georgia, United States
BD

Bhabesh Dutta, PhD

Professor and Extension Vegetable Disease Specialist
University of Georgia
Tifton, Georgia, United States
MB

Marin Brewer

Professor of Mycology and William Terrell Distinguished Professor
Department of Plant Pathology, University of Georgia, Athens
Athens, Georgia, United States

Abstract Text: Watermelon, cucumber, and cantaloupe are major cucurbit crops grown in the United States, playing a key role in the fresh produce market. However, their production is often impacted by diseases, particularly anthracnose caused primarily by Colletotrichum orbiculare. Recent outbreaks have been reported in Florida, Georgia, South Carolina, North Carolina, Virginia, Delaware, and New York. In recent years, growers in the eastern U.S. have increasingly relied on QoI fungicides, like azoxystrobin, to manage cucurbit anthracnose. However, a noticeable reduction in fungicide effectiveness has been observed, especially for cucumber, suggesting potential resistance. We identified the F129L partial resistance mutation in the cytochrome B gene of C. orbiculare in Georgia isolates from cucumber (n=11) and cantaloupe (n=5), but not from watermelon (n=11). This mutation is associated with higher EC₅₀ values and potentially linked to emerging anthracnose outbreaks. To facilitate rapid detection of resistance, we have developed a PCR-based marker for the F129L mutation. The association of the marker with increased EC₅₀ values is being evaluated on 50 additional isolates from watermelon, cucumber, and cantaloupe from Georgia, South Carolina and Florida. Investigating resistance mechanisms is essential for understanding the pathogen's response to QoI fungicides, particularly if there are differences in populations among the cucurbit hosts. These findings support the development of efficient detection methods and ultimately contribute to improved disease management strategies.