Semester of Graduation

Fall 2017

Degree

Master of Science (MS)

Department

Department of Plant Pathology and Crop Physiology

Document Type

Thesis

Abstract

Aspergillus flavus is a saprophytic ascomycete that can also actively invade the seed of crops and potentially contaminate them with harmful aflatoxins. Management of A. flavus currently relies mostly on biocontrol. However, there is still a lot to learn about its biology and ecology so the current approach can be improved. An A. flavus population survey was undertaken during the fall of 2014 across eight Mississippi River states to determine population diversity and geographic distribution of VCGs. Isolates from corn and soil were also characterized for VCG, sclerotial morphotype, mating type, cyclopiazonic acid, and aflatoxin production in order to determine trait uniformity within VCGs and those VCGs traits which may be associated with corn infection. From a collection of 339 soil and 204 kernel isolates, 18 multiple-isolate VCGs were determined. Four VCGs accounted for 54% of soil and 48% of total kernel populations and these were the only ones recovered from both niches. Nine VCGs were only recovered from the soil population and 5 from corn kernels. Two VCGs were widely distributed across the 8-state transect and they were the same most frequently isolated from corn kernels in Louisiana in 2007. Results also indicate that the A. flavus metapopulation along the Mississippi River was highly genetically diverse as reflected by the diversity of VCGs. Southern populations were more diverse, and the northern region showed higher clonal fractions. Mating type MAT1-2 and high CPA production were associated with corn infectors, which were mainly of the L-morphotype. The soil niche had both, S and L-sclerotial morphotypes and although ~70% of isolates from both niches produced CPA, kernel isolates produced higher concentrations and support the report that CPA is a pathogenicity factor for A. flavus. These results give insight into important traits for corn infection, for both toxigenic and atoxigenic strains, which may be key in the improvement of biological control strategies. Characterizing the diversity of VCGs and their distribution over a 1500 km transect spanning important corn growing areas in the US, has allowed creation of a quantitative baseline of VCGs which can be used for monitoring changes in biodiversity over time.

Date

11-13-2017

Committee Chair

Damann, Kenneth

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