Recovery of Pantoea ananatis, causal agent of center rot of onion, from weeds and crops in Georgia, USA

Abstract

Center rot of onion, caused by Pantoea ananatis, has been a problem of sweet onions in Georgia since 1997. A polymerase chain reaction (PCR) protocol was developed to screen for populations of P. ananatis on plant surfaces. Plant samples producing a positive PCR reaction were targeted for further processing to culture the bacterium. In a survey of the Vidalia onion-growing region of Georgia, we detected and cultured P. ananatis from 25 asymptomatic weed species, which included commonly occurring weeds such as crabgrass ( Digitaria sanguinalis), Florida beggarweed ( Desmodium tortuosum), Florida pusley ( Richardia scabra), sicklepod ( Cassia obtusifolia), Texas Millet ( Panicum texanum), tall verbena ( Verbena bonariensis) and yellow nutsedge ( Cyperus esculentus). In addition, the bacterium was recovered from crop plants such as Bermuda grass ( Cynodon dactylon), cowpea ( Vigna unguiculata) and soybean ( Glycine max) . Based on the field survey and tests with strains held in storage in the Coastal Plain Experiment Station culture collection, we concluded that P. ananatis was in Georgia prior to 1997, and was distributed widely on weeds and crops throughout southern Georgia.