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POSTERS: Disease Detection and Diagnosis I

P-209 - Direct assessment of QoI fungicide resistance from leaves in Cercospora leaf blight of soybean

Monday, August 4, 2025
3:45 PM - 4:30 PM HST
Location: Exhibit Hall 3

    Presenting Author(s)

  • SR

    Stephanie Karen Ramos

    Graduate Student
    Louisiana State University
    Baton Rouge, Louisiana, United States

    • Author(s)

  • DM

    David Moseley

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

  • ED

    Ernesto Da Silva

    LSU
    Baton Rouge, Louisiana, United States

  • JA

    Jonathan Patrick Amie

    LSU
    Baton Rouge, Louisiana, United States

  • FD

    Felipe Dalla Lana

    Assistant Professor
    Louisiana State University
    Rayne, 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:

Cercospora leaf blight (CLB) has been the primary foliar disease of soybean in the mid-South for over a decade with management complicated by the evolution of fungicide resistance. Geographic delineation of fungicide resistance and use of alternate chemistries are critical for effective control of CLB. Although resistance to QoI (quinone outside inhibitor) fungicides was first documented in 2015, its frequency is known to vary by field. Thus, QoI applications may remain effective when sensitive isolates dominate. Two protocols – LAMP (loop-mediated isothermal amplification) and PCR-RFLP (polymerase chain reaction-restriction fragment length polymorphism) – were tested to quickly detect the G143A mutation associated with QoI resistance. Both methods identified 77% of 147 isolates as QoI resistant, but only LAMP detected resistance directly from artificially inoculated leaves. The LAMP assay was then used on 320 leaf disks from ten georeferenced CLB symptomatic soybean samples, collected across four fields in LA. High frequency of QoI resistance was present in all fields (80%), regardless of fungicide use, with spatial clustering in two fields (Moran’s I 0.404 and 0.092, p< 0.05). Species-specific qPCR assays to detect CLB pathogens identified Cercospora cf. flagellaris on 98% of the leaf disks and C. cf. sigesbeckiae on 2%. The LAMP assay had 96% accuracy and 99% sensitivity with the key advantage of detecting QoI resistance without pathogen isolation. The data will be used to guide sampling for fungicide resistance.