Semester of Graduation
Fall 2024 (december)
Degree
Master of Science (MS)
Department
Plant Pathology and Crop Physiology
Document Type
Thesis
Abstract
Cercospora leaf blight (CLB) has been the primary foliar disease impacting the soybean crop in the mid-South for over a decade. A poor understanding of disease epidemiology and the prevalence of fungicide resistance have added complexity to management efforts. Recent findings suggest that airborne conidia play a significant role in the outbreak of CLB. We investigated the relationship between weather variables and conidial release using multi-site, multi-year spore trapping data. The findings confirm that C. cf. flagellaris is the dominant CLB pathogen, contributing significantly more conidia than C. cf. sigesbeckiae and C. kikuchii in soybean fields across Arkansas, Mississippi, and Louisiana. Individual and combined weather variables from local weather stations did not correlate with conidial peaks at LA locations when tested for the week of and the previous week of spore trapping. A deeper understanding of the biology of CLB pathogens by using controlled environmental conditions may be needed to identify weather variables associated with sporulation and spore release. To guide fungicide resistance management, we tested if quick resistance detection protocols can provide a fine-scale spatial characterization of fungicide resistance. Two rapid QoI (Quinone outside inhibitor) fungicide resistance detection protocols – loop-mediated isothermal amplification (LAMP) and polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) – were tested directly on leaves for detecting the G143A mutation associated with QoI resistance. Although both LAMP and PCR-RFLP identified 113 of 147 isolates (76.9%) collected from across the U.S. as QoI resistant, only the LAMP assay could detect resistance directly on leaves. Using ten georeferenced CLB symptomatic soybean samples collected from four fields in four LA parishes, the LAMP assay indicated that QoI resistance was present in all fields (79.69% of 320 leaf disks), regardless of fungicide usage. Further in only 4.375% of the cases, did two leaf disks originating from a single leaflet differ in resistant/sensitive results, suggesting an overall uniformity of QoI resistance among the selected parishes in Louisiana. The protocol developed here can be used to determine the number of samples needed to accurately detect low levels of resistance in the field and enhance the management strategies for CLB.
Date
11-1-2024
Recommended Citation
Ramos, Stephanie Karen, "ADDRESSING KNOWLEDGE GAPS IN DISEASE EPIDEMIOLOGY AND DETECTION OF FUNGICIDE RESISTANCE IN CERCOSPORA LEAF BLIGHT OF SOYBEAN" (2024). LSU Master's Theses. 6058.
https://repository.lsu.edu/gradschool_theses/6058
Committee Chair
Sara Thomas-Sharma