Survival Sites Discovered for the Bacterial Spot Pathogen of Pepper

Situation or issue identification: Bell pepper is an important crop in Florida, especially on the mineral soils of the lower east coast and in southwestern vegetable-growing areas. In a recent year, 20,300 acres were harvested in the state with a value of $188 million. Bacterial spot, caused by Xanthomonas campestris pv. vesicatoria, has been a major disease threat to the pepper industry for over 50 years. Sprays of copper-based bactericides have been a mainstay of the management program for bacterial spot, but only marginal success has been attained. We've shown that epiphytic populations of the pathogen within buds escape potentially lethal doses of copper, accounting, in part, for lack of copper efficacy. In one test, copper sprays reduced X. campestris pv. vesicatoria populations by 99% on exposed leaves, compared to only 51% in buds. Epiphytic populations were also consistently higher on cultures without resistance genes. Populations on leaves of susceptible cultivar Jupiter were 2-3 log units higher than on Boynton Bell with the Bs2 gene for resistance to races 1, 2, 3 of the pathogen.

Rationale for research support resources: Growers may be applying up to 15 applications of copper, often in a vain attempt, to manage bacterial spot. Because these studies show that significant populations of the pathogen survive in buds, where they are protected from copper exposure, we may be able to educate growers in less dependence on these questionable sprays. Reductions in sprays will have positive economic and environmental impacts.

Measurable or potential impact in terms of social, economic, and/or environmental factors resulting from expenditure of research support funds: Residual populations X. campestris pv. vesicatoria on leaves of resistant cultivars are one million-fold less than in susceptible cultivars. This translates into a 50% reduction in disease and a net return of approximately 700 boxes of pepper per acre. If growers see the lack of benefit of copper sprays because of populations in buds, 3-5 copper applications per acre may be saved, which is equivalent to 60,000 pounds less copper in the environment annually.

Collaborating organizations/agencies and teaching/research/extension partnerships: This work has involved collaboration between University personnel, private seed companies, individual growers, and the Florida Bell Pepper Exchange.

For more information contact: Kenneth L. Pernezny