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Transmission of Pantoea ananatis and P. agglomerans, Causal Agents of Center Rot of Onion (Allium cepa), by Onion Thrips (Thrips tabaci) Through Feces

First, sixth, and seventh authors: Department of Plant Pathology, Coastal Plain Experiment Station, University of Georgia, Tifton, GA 31793; second and third authors: Department of Entomology, Coastal Plain Experiment Station, University of Georgia, Tifton, GA 31793; fourth author: Complex Carbohydrate Research Center, University of Georgia, Athens, GA 30602; and fifth author: Department of Entomology, University of California, Davis, CA 95616.

Frankliniella fusca, the tobacco thrips, has been shown to acquire and transmit Pantoea ananatis, one of the causal agents of the center rot of onion. Although Thrips tabaci, the onion thrips, is a common pest of onions, its role as a vector of P. ananatis has been unknown. The bacterium, P. agglomerans, is also associated with the center rot of onion, but its transmission by thrips has not been previously investigated. In this study, we investigated the relationship of T. tabaci with P. ananatis and P. agglomerans. Surface-sterilized T. tabaci were provided with various acquisition access periods (AAP) on onion leaves inoculated with either P. ananatis or P. agglomerans. A positive exponential relationship was observed between thrips AAP duration and P. ananatis (R² = 0.967; P = 0.023) or P. agglomerans acquisition (R² = 0.958; P = 0.017). Transmission experiments conducted with T. tabaci adults indicated that 70% of the seedlings developed center rot symptoms 15 days after inoculation. Immunofluorescence microscopy with antibodies specific to P. ananatis revealed that the bacterium was localized only in the gut of T. tabaci adults. Mechanical inoculation of onion seedlings with fecal rinsates alone produced center rot but not with salivary secretions. Together these results suggested that T. tabaci could efficiently transmit P. ananatis and P. agglomerans.