Author ORCID Identifier

https://orcid.org/0000-0003-1403-4888

Year of Publication

2022

Degree Name

Master of Science (MS)

Document Type

Master's Thesis

College

Agriculture, Food and Environment

Department/School/Program

Plant Pathology

First Advisor

Dr. Lisa Vaillancourt

Abstract

Fusarium Head Blight (FHB), caused by Fusarium graminearum sensu stricto and other members of the F. graminearum species complex (FGSC), is a plant disease that occurs on cereal crops worldwide. FHB causes yield losses not only by reducing grain weight, but also by contaminating the kernels with dangerous trichothecene mycotoxins, especially deoxynivalenol (DON). There is a high degree of genotypic and phenotypic variation among pathogen species and strains, but current FHB risk assessment models and treatments do not account for pathogen diversity. Therefore, it is difficult to predict what will happen if a new, potentially more aggressive variant is introduced, or if changes in the environment favor one genotype over another. Fusarium graminearum is homothallic, and self-fertility is regulated by the complex MAT1 locus that encodes two genes called MAT1-1-1 and MAT1-2-1. Previous studies have demonstrated that deletion of either gene produces an obligately heterothallic strain that can only outcross with a strain of the opposite type. The goal of my thesis research was to screen a collection of independent MAT1-1-1 and MAT1-2-1 (MAT) deletion mutants to identify appropriate test maters that could be used to cross with wild type (WT) strains and facilitate genetic analyses of traits of interest. Because the deletion strains engage only in heterothallic mating, it solves the problem of identifying outcrossed perithecia. The ideal mating tester strain should be phenotypically similar to the WT in pathogenicity and toxigenicity, and should also grow normally in culture, be highly female-fertile, and produce abundant ascospore progeny that exhibit normal marker segregation patterns. Many of the deletion strains, especially the MAT1-2-1 deletions, were significantly less pathogenic and fit compared with their WT progenitor strain PH-1. Strains also varied widely in female fertility and levels of interfertility with other mutant and WT strains. Two highly female-fertile MAT1-1-1 deletion strains that had WT levels of pathogenicity, toxigenicity, and fitness were used in test crosses with several other strains. These included a MAT1-2-1 deletion strain with reduced fitness and pathogenicity, and several WT strains including PH-1, another strain of F. graminearum ss. (Gz3639), and F. meridionale, another member of the FGSC that can cause FHB. Antibiotic resistance, MAT alleles, chemotypes, CAPs markers, and fertility all had expected 1-1 segregation patterns in the crosses and expected linkage relationships. These mating tester strains can be used in the future to identify novel genetic markers associated with fitness and pathogenicity that could be incorporated into multi-locus genotyping assays to monitor and predict population shifts.

Digital Object Identifier (DOI)

https://doi.org/10.13023/etd.2022.298

Funding Information

U.S. Wheat & Barley Scab Initiative 2019-2022

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