Wednesday, April 18, 2018 at 12:20pm
Graduate Student Exit Seminar, PPPMB, Cornell University
My work is focused on the diversity and abundance of fungi in the human environment and fungi associated with food. I am particularly interested in fungal communities of food spoilage, as well as fungi that survive in extreme environments such as preserved foods and in our homes. The implications of contact with and consumption of these organisms and their associated secondary metabolites intrigue me. My research is currently focused on thermotolerant fungi, which survive conventional food processing, and cause spoilage. I am interested in the diversity of these organisms as well as the variation in physiological traits among isolates that allow them to cause problems.
Paecilomyces niveus is an important heat-resistant spoilage mold of fruit products which produces the mycotoxin, patulin. This understudied ascomycete is regarded as a soil-borne contaminant and known to synthesize the regulated mycotoxin patulin, a virulence factor for other apple diseases. My goals were to determine the occurrence of P. niveus in New York soils, including orchards, assess the ability of P. niveus to infect apples under post-harvest and field conditions, test whether infected apples can be a source of spoilage fungi in the finished apple juice concentrate, and evaluate the sensitivity of isolates to post-harvest fungicides. Paecilomyces niveus was isolated from 30% of soil samples. When screened, isolates from agricultural environments showed reduced sensitivity to difenoconazole, fludioxonil, and pyrimethanil compared to isolates from non-agricultural environments. Paecilomyces niveus was demonstrated to infect apples through wounds, both under post-harvest conditions and in the orchard. This newly described disease, Paecilomyces rot, causes symptoms similar to other apple diseases, including bull’s-eye rot. Despite thermal processing, juice concentrate made from infected fruit contained viable P. niveus propagules and > 50 ppb, the legal limit for patulin (FDA). This work suggests P. niveus may be introduced to wounded fruit from orchard soils, and go on to cause spoilage and mycotoxin problems in processed products. Due to its superficial similarity to other diseases, Paecilomyces rot may be overlooked. Proposing a novel explanation for the episodic nature of P. niveus contamination, this research links apple disease with food spoilage. Controlling Paecilomyces rot with fungicides may be complicated by selection for fungicide resistance among diverse isolates, which is the subject of ongoing work.