Date of Award


Document Type


Degree Name

Master of Science (MS)


Plant and Environmental Science

Committee Chair/Advisor

Dr. Hehe Wang

Committee Member

Dr. Guido Schnabel

Committee Member

Dr. Juan Carlos Melgar


Xanthomonas arboricola pv. pruni (Xap) is an economically important pathogen causing bacterial spot of stone fruits worldwide. In the southeastern US management for this disease relies on copper and oxytetracycline (OTC) sprays, yet disease incidence remains high especially when the environmental conditions are conducive (warm and rainy). To further complicate disease management copper tolerant and OTC resistant (OTCR) strains of Xap have been reported in the southeastern peach orchards. complicating disease management. Therefore, we aim to evaluate potential chemical and biological alternatives for disease management. The first objective was to evaluate a novel nano nanoformulation Bz (Zinc Borate) with OTC against Xap. In the lab, Bz alone exhibited bactericidal effect against all five Xap strains tested; it showed an overall additive effect when combined with OTC and a slight synergistic effect was observed against one OTC sensitive strain. The second objective was to evaluate the impact of fungicide spray programs and other novel chemicals on managing Xap strains with different levels of sensitivity to copper and OTC. In the lab, 30 chemicals were evaluated against five Xap strains; 11 fungicides at the maximum label rate and 4 other novel chemicals significantly reduced Xap colony formation on media; 9 chemical were further tested at the half rate and five completely inhibited the Xap growth. Seven chemicals were tested on peach trees in the greenhouse against an OTCR strain; most of them (Ziram, AmTide, Maneb, and Manzate) and Quatrain significantly reduced the disease incidence and severity on leaves; Zinkicide reduced the disease severity only. The third objective was to evaluate biological agents for Xap control. In the lab, all 17 Bacillus strains tested developed zones of inhibition against all four Xap strains. In the greenhouse, 5 biological agents were tested with one-time spray, but none were able to reduce disease on peach leaves inoculated with an OTCR strain. This study will provide information for developing new chemical and biological alternatives for management of bacterial spot in peach.

Included in

Life Sciences Commons



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