Shrimp Shells Loom Large in Fight Against Apple Scab
August 11, 2020 Researchers from the University of New Hampshire and Penn State University are investigating the effectiveness of chitosan — a byproduct of mostly shrimp shells from the seafood industry — in the management of apple scab for Northeast farmers.
Previous research involving chitosan has focused on the reduction of postharvest disease. Led by UNH graduate student Liza DeGenring, researchers would like to extend that knowledge to investigate the effect of a chitosan application during crop production and in combination with an application of biopesticides.
“Reduced fruit quality is a major concern for the New Hampshire tree fruit industry since New Hampshire growers primarily market retail sales of fresh apples through pick-your-own, farm stands, and direct sales to grocery stores,” DeGenring said. “Apple scab lesions on the fruit can result in decreased revenue to the grower due to consumers’ low threshold for imperfections on their apples.”
Although many beneficial microorganisms associated with plants have been commercialized and sold as biopesticides for use in agriculture to reduce plant diseases, widespread adoption of biopesticides has been limited due to inconsistencies in their effectiveness.
“Because biopesticides are living products, their activity is affected by environment. Biopesticides often fail to grow and maintain high enough population levels in the orchard or do not produce antifungal compounds at levels necessary to suppress the disease,” DeGenring said. “It is increasingly recognized that solving these issues is key to increasing adoption of biopesticides. I am investigating a way to enhance biopesticide effectiveness using chitosan. There is evidence that chitosan may act as a food source for the biopesticides and stimulate production of antifungal enzymes, thereby enhancing their usefulness.”
DeGenring is working with NH Agricultural Experiment Station researcher Anissa Poleatewich, who is also an Assistant Professor of Plant Pathology and her faculty advisor. Collaborators include George Hamilton and Jeremy DeLise, both with UNH Cooperative Extension, and Kari Peter from the Pennsylvania State University Fruit Research and Extension Center.
Apple scab, caused by the fungus Venturia inaequalis, can cause up to 100% crop loss and significant reduction in fruit marketability. According to the USDA National Agricultural Statistics Service, the market value of apples nationwide was $2.4 billion. The New Hampshire tree fruit industry includes 228 farms, growing 1,701 acres of tree fruit, valued at $9.3 million.
“UNH has a historical reputation of conducting apple scab research,” Poleatewich said. “Much of what we know today about the disease is based on work done by William MacHardy, Professor Emeritus of Plant Biology. New Hampshire tree fruit growers have a strong history of collaboration with UNH to develop and adopt more environmentally and economically sustainable practices. In the 1980s, MacHardy and colleagues developed disease-forecasting models that growers still use today to predict outbreaks and apply fungicides only when disease risk is high. New Hampshire growers also have adopted integrated pest management, which incorporates cultural, biological, and chemical practices to suppress disease. Even with these advances, apple scab continues to be a major nemesis to tree fruit growers.”
To combat apple scab disease, growers primarily rely on sanitation and fungicide applications in their orchards. However, there is increasing pressure by consumers to decrease the use of synthetic chemicals due to concerns of adverse effects on non-pest species and human health, as well as the risk of pathogen resistance development with regular fungicide applications. Both the potential decrease in consumer demand and increased costs of resistant pathogen management can decrease producer profits.
“Both farmers and apple consumers would like alternative options for controlling apple scab. Chitosan has shown promise in other research in reducing disease, and there is a potential to use it to suppress disease in tree fruit production,” DeGenring said.
According to DeGenring, the success of sustainable agriculture in the United States will increasingly rely on the integration of biologically based methods with conventional agricultural practices that rely on fungicides. The scientific and agricultural community has begun to recognize the critical role microorganisms, such as bacteria and fungi, and their metabolites play in agro-ecosystem health.
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