P-125 - Resistance to single- and multi-site fungicides detected in soil-borne fungal pathogens of soybean

Monday, August 4, 2025

3:45 PM - 4:30 PM HST

Location: Exhibit Hall 3

Presenting Author(s)

KM

Kelvin Kagondu Muchiri (he/him/his)

Department of Plant Pathology, University of Nebraska-Lincoln
Lincoln, Nebraska, United States

Author(s)

DM

Dylan Mangel, n/a

Soybean Pathology Extension Specialist
University of Nebraska - Lincoln
Lincoln, Nebraska, United States
KB

Kyle C. Broderick, n/a

Associate Extension Educator
University of Nebraska-Lincoln
Lincoln, Nebraska, United States
FM

Febina Mathew, PhD

Associate Professor
Department of Plant Pathology, North Dakota State University, Fargo, ND 58102
Fargo, North Dakota, United States
TG

Teddy Garcia-Aroca, PhD

Assistant Professor
Department of Plant Pathology, University of Nebraska-Lincoln
Lincoln, NE, USA

Abstract Text: Over-reliance on fungicide application to control fungal pathogens has led to decreased sensitivity to commonly used fungicides including QoI’s, DMI’s and SDHI’s. However, our understanding of relative levels of resistance in soil-borne pathogens is not well documented. In this study, we investigated the status of fungicide resistance in soil-borne pathogens of soybean in Nebraska. Diseased soybeans were collected across 23 counties in Nebraska and obtained fungal isolates (n=309) were identified to genus or species level using phylogenetic analyses of ribosomal DNA and TEF1-α sequences. Representative isolates of Fusarium solani, F. oxysporum, Rhizoctonia solani, and Diaporthe longicolla were used in fungicide resistance experiments. Resistance screening was conducted in vitro using amended agar methods, with serial dilutions per fungicide and mycelial growth measured over time. Our results suggest differences between species (p < 0.0001) and fungicide (p < 0.0001), with a strong interaction effect (F = 13.80, p < 0.0001), indicating species-specific responses. Additionally, all fungicide dilutions significantly reduced growth compared to control (p < 0.0001), however, fungicide efficacy decreased at higher dilutions. F. oxysporum exhibited the highest resistance, while F. solani and D. longicolla showed no significant resistance (p = 0.3019). We detected single and unexpected multi-site fungicide resistance in some of the species. These findings will provide the knowledge needed in the development of effective management strategies against soil-borne pathogens of soybean.