Doctor of Philosophy (PhD)
Plant Pathology and Crop Physiology
Aspergillus flavus is an ascomycete fungus impacting agriculture, public and environmental health due to production of acutely-toxic, carcinogenic aflatoxins in oil seed crops, especially corn in Louisiana, and lung infections of immunocompromised patients resulting in a leading cause of AIDS patients’ deaths globally. The most effective aflatoxin mitigation strategy, biocontrol by atoxigenic A. flavus presents several concerns including: dissemination of a human pathogen, possible sexual reproduction and reliance on precise environmental conditions. Several aspects of A. flavus biology were investigated to potentially improve treatments. Studies investigated how genotypically diverse members within the A. flavus population interact with other population members and across kingdoms, and how these interactions ultimately regulate aflatoxin production and contamination of corn. A main finding was, biocontrol strains inhibited aflatoxin production of corn-adapted strains more completely than soil-adapted strains. Biocontrol strains inhibited aflatoxin by production of secreted inhibitory chemicals in addition to touch and direct replacement. Corn-adapted strains produced more inoculum and infected more kernels at low inoculum levels than soil-adapted strains; a likely explanation for differences between corn and soil A. flavus populations. Including differences in male and female gametic structure production between strains in estimates of effective breeding population size indicated sexual reproduction was less likely than expected based on mating type distributions and sexual reproduction would be more likely after harvest, when the numerous male corn-adapted population comes in contact with the female population in the soil. Finally, gases produced by clones can inhibit or stimulate aflatoxin production of neighboring clones. The main implication of this research is to improve biocontrol efficacy and minimize infection by highly toxic soil-adapted strains, corn should not come in contact with soil after harvest. Applying currently available male biocontrol strains to the soil dominated by females should greatly increase the chance for sexual reproduction during cultivation. The speed of sexual reproduction in the field needs to be investigated, as well as the use of infertile biocontrol strains. The inhibitory secreted and volatile chemicals produced by A. flavus need to be identified to help produce a fungus-free biocontrol product.
Sweany, Rebecca R., "Investigations into Aspergillus flavus Infection of Corn and Regulation of Aflatoxin Production by Volatiles and Biocontrol Strains" (2019). LSU Doctoral Dissertations. 4780.