Date of Award

Fall 2023

Project Type

Dissertation

Program or Major

Animal and Nutritional Sciences

Degree Name

Doctor of Philosophy

First Advisor

Anissa Poleatewich

Second Advisor

Rebecca Sideman

Third Advisor

Cheryl Smith

Abstract

Annual crop losses caused by plant diseases are estimated worldwide at 220 billion US dollars. Conventional fungicides are the primary means to control these diseases, however there are growing concerns over human health, effects on non-target species, and environmental contamination. Furthermore, many plant pathogens have developed fungicide resistance due to overexposure to chemicals with single modes of action. There is a worldwide trend to explore alternative tools to reduce the use of synthetic fungicides while continuing to reduce plant disease. Among these control strategies are the use of antagonistic microorganisms (biopesticides) and naturally occurring compounds that have fungicidal activity. Chitosan is a promising natural compound documented to have antifungal and disease suppressive effects. Chitosan has been used successfully as a postharvest application to prevent storage rot and extend shelf life of perishable fruits and vegetables. There is limited research on preharvest application of chitosan for reducing pre-harvest and post-harvest diseases. The overall goal of this research was to investigate biopesticide-chitosan synergisms in two cropping systems to improve biological control of pre- and post-harvest plant diseases. These systems were chosen to represent two plant types (woody and herbaceous) and two production industries (perennial field production and greenhouse production). The herbaceous cropping system focused on the investigation of chitosan’s ability to suppress gray mold on petunia leaves caused by Botrytis cinerea using in vitro and in planta approaches. In this research I found that chitosan products, both reagent grade and commercial, reduced B. cinerea growth in vitro and lesion size in planta. For the woody cropping system, I focused on the investigation of chitosan’s efficacy and the potential synergisms of chitosan and a biopesticide to suppress fungal above-ground apple diseases. Results indicate that pre-harvest chitosan applications can reduce foliar diseases on apple but was most effective when overlayed onto a grower standard treatment. Additionally, the addition of chitosan to a biopesticide spray did not enhance the biopesticide’s efficacy under the research conditions. Postharvest chitosan treatments greatly reduced postharvest incidence and severity of rots caused by Penicillium expansum and Colletotrichum fioriniae. Results from this research demonstrate that chitosan can suppress foliar and fruit fungal diseases and has the potential to play a role in a disease management program for reduction of above-ground fungal pathogens under various cropping systems.

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