Submitted to: Acta Horticulture Proceedings
Publication Type: Proceedings
Publication Acceptance Date: April 10, 2010
Publication Date: August 10, 2010
Citation: Macarisin, D., Wisniewski, M.E., Droby, S., Bauchan, G.R. 2010. A role for reactive oxygen species in postharvest biocontrol. Acta Horticulture Proceedings. Technical Abstract: Reactive oxygen species (ROS) play an important role in plant defense responses against pathogens. There is evidence that microbial biocontrol agents also induce a transient production of ROS in a host plant which triggers local and systemic defense responses. In this study, we explored the ability of yeast antagonists to induce defense-related oxidative responses in fruits. We observed that two antagonist yeasts, Metschnikowia fructicola and Candida oleophila, generate greater levels of super oxide anion on intact fruit surfaces (poor in nutrients) than when they are grown on a nutrient-poor agar medium. When the antagonists are applied to wounded fruit (rich in nutrients), accumulation of super oxide anion detected by nitro blue tetrazolium staining occurs more rapidly than when the yeast are grown on a nutrient-rich medium. Using laser scanning confocal microscopy, we also observed that the application of M. fructicola and C. oleophila into citrus and apple fruit wounds was correlated with an increase in H(2)O(2) accumulation in host tissue. As early as 18 hours after inoculation, the level of H(2)O(2) in inoculated, wounded tissue was 4-fold greater than in control wounds inoculated only with water. Yeast continued to stimulate H(2)O(2) production in citrus fruit up to 66 hours after inoculation, and H(2)O(2) levels were still 3-fold above the control. Living yeast cells were detected in fruit wounds at this time point indicating the ability of M. fructicola to tolerate host ROS, which has been suggested to be an intrinsic characteristic of effective yeast antagonists. Collectively, our data, along with our earlier report on the importance of H(2)O(2) production in the defense response of citrus flavedo to postharvest pathogens, indicate that the ability of yeasts to induce an oxidative response in fruit tissue may be an essential aspect of yeast species and strains that serve as effective postharvest biocontrol agents.