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Transmission of Pantoea ananatis, Causal Agent of Center Rot of Onion, by Tobacco Thrips, Frankliniella fusca

Center rot of onion, caused by Pantoea ananatis, was first reported on onion in Georgia in 1997 and has continued to reduce yields and cause postharvest losses. In a previous study, we developed a nondestructive assay that demonstrated an association between P. ananatis and approximately 10% of the tobacco thrips, Frankliniella fusca, surveyed. In this study, we report that all strains of P. ananatis, isolated from surface-sterilized, crushed thrips, were pathogenic when inoculated onto greenhouse-grown onion plants. Furthermore, when 6 to 12 thrips harboring populations of P. ananatis of 1 × 10³ CFU ml^-1 or greater were placed on healthy onion seedlings to feed, disease transmission occurred in 52% of the plants challenged. Incubation periods ranged from 4 to 9 days. Bacteria isolated from symptoms typical of those associated with center rot were characterized and identified as P. ananatis. In contrast, an equal number of plants remained healthy for up to 28 days after being exposed to the same number of tobacco thrips that were identified as being free of P. ananatis.