Semester of Graduation

Spring 2023


Master of Science (MS)


Plant Pathology and Crop Physiology

Document Type



Cercospora sojina is the causal agent of the fungal disease frogeye leaf spot (FLS) in soybeans. Management of this disease consists of foliar application of fungicides and the use of resistant cultivars. However, fungicide resistance has been detected in C. sojina populations and characterization of host resistance genes is relatively limited. To overcome the latter obstacle, we aimed to identify novel resistance genes using quantitative image analysis of the SoyNAM population. Two image analysis workflows using ImageJ and PlantCV were optimized and implemented to increase reproducibility and reduce subjectivity. The quantitative measurements included disease severity, lesion count, and average lesion size. The SoyNAM parental lines showed a wide range of host reactions to two C. sojina isolates compared to a suceptible and resistant control. The parental line Prohio exhibited high levels of resistance comparable to the resistant control. The Prohio × IA3023 bi-parental recombinant inbred line population was inoculated with two C. sojina isolates and rated using quantitative measurements via image analysis and a categorical scale. Single marker association analyses identified a locus on chromosome 16, likely corresponding to Rcs3, associated with resistance to both isolates and by all measured parameters. Multiple small effect loci were identified throughout the genome which were specific for each isolate. Linkage disequilibrium (LD) blocks were calculated for the major chromosome 16 locus, as well as for loci on chromosomes 5 and 19. Candidate genes with functions associated with the host defense response were identified within each LD block. Taken together, image analysis and quantitative measurements of disease led to insight behind the genetics of resistance to FLS.



Committee Chair

Richards, Jonathan K.