High-Throughput Microplate Assay to Detect QoI-Resistance in the Cercospora leaf blight Pathogen Complex of Soybean

Monday, August 4, 2025

12:45 PM - 1:00 PM HST

Location: Room 313 C

Presenting Author(s)

BC

Beatriz M. Carvalho

Postdoctoral Researcher
Department of Plant Pathology & Crop Physiology, Louisiana State University
Baton Rouge, LA, USA

Author(s)

AD

Abdulkadir I. Dalha (he/him/his)

Post Doctoral Researcher
Department of Plant Pathology & Crop Physiology, Louisiana State University
Baton Rouge, Louisiana, United States
PD

Pedro Henrique Dias dos Santos

Postdoctoral Researcher
Department of Plant Pathology & Crop Physiology, Louisiana State University
Baton Rouge, Louisiana, United States
SR

Stephanie Ramos

Department of Plant Pathology & Crop Physiology, Louisiana State University
Baton Rouge, Louisiana, United States
JA

Jonathan Patrick Amie

LSU
Baton Rouge, Louisiana, United States
TA

Tom W. Allen

Extension/Research Professor
Delta Research & Extension Center, Mississippi State University
Stoneville, Mississippi, United States
TS

Terry Spurlock, PhD

Associate Professor
Department of Entomology and Plant Pathology. University of Arkansas System Division of Agriculture
Little Rock, Arkansas, United States
DM

David Moseley

Assistant Professor/Soybean Specialist
Dean Lee Research & Extension Center, Louisiana State University
Alexandria, Louisiana, United States
TP

Trey Price, n/a

Associate Professor
Macon Ridge Research Station, Louisiana State University, Winnsboro, LA 71295
Winnsboro, Louisiana, United States
BP

Boyd Padgett

Professor
Dean Lee Research & Extension Center, Louisiana State University
Alexandria, Louisiana, United States
JR

Jonathan K. Richards

Associate Professor
Department of Plant Pathology & Crop Physiology, Louisiana State University, Baton Rouge, LA 70803
Baton Rouge, Louisiana, United States
VD

Vinson P. Doyle

Associate Professor
Department of Plant Pathology & Crop Physiology, Louisiana State University, Baton Rouge, LA 70803
Baton Rouge, Louisiana, United States
ST

Sara Thomas-Sharma

Assistant Professor
Department of Plant Pathology & Crop Physiology, Louisiana State University
Baton Rouge, Louisiana, United States

Abstract Text:
The quinone outside inhibitor (QoI) fungicides are widely used to manage Cercospora leaf blight (CLB) of soybean across the Mid-southern U.S. However, QoI-resistant Cercospora isolates were initially documented in 2015 from LA. Since the frequency of resistant isolates can vary by geographic region, rapid and reliable screening methods are needed to determine the frequency of QoI resistance in a region. We optimized a high-throughput microplate method to evaluate the resistance of Cercospora isolates to QoI fungicides. This new method was validated against the conventional assay using 10 Cercospora isolates known to be QoI-resistant or -sensitive based on the presence of the G143A substitution. The isolates were tested with azoxystrobin in two formulations – commercial-grade (22.9% active ingredient) and technical-grade (99.5% active ingredient) – at six concentrations (0, 0.01, 0.1, 1.0, 10, and 100 ppm). Each isolate was tested in triplicate, resulting in 360 plates/wells. The conventional assay was evaluated using a digital caliper and the microplate assay was evaluated spectrophotometrically at 600 nm. Assays were evaluated at multiple time points (0 to 192 h post-inoculation) and will be used to generate growth curves and EC₅₀ values to compare the two methods. If the microplate assay is suitable as a rapid tool for assessing QoI resistance in Cercospora isolates, the assay will also be adapted to measure resistance to additional active ingredients currently used for CLB management.