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Poster: Biology & Disease Mgmt: Bacteriology


Epiphytic survival of Pantoea ananatis on Florida Pusley (Richardia scabra L.)
B. DUTTA (1), R. Gitaitis (1), F. Anderson (1) (1) the university of georgia, U.S.A.

Pantoea ananatis, the causal organism of center rot of onion (Allium cepa L.), can survive on different weeds, but in a previous survey it was most commonly found on Florida pusley (Richardia scabra L.). The epiphytic survival of P. ananatis on Florida pusley under different temperature and moisture regimes was investigated. Weed seedlings were spray-inoculated with 103 colony forming units (CFU)/ml of rifampicin-resistant strain Pan 97-1rif and incubated in a growth chamber at 15.5° or 21.1°C at 65% RH for 96 h, which represented mean environmental conditions during mid-March to mid-May in Vidalia, GA. P. ananatis survived for 96 h when incubated at 21.1°C with a mean population of 3.2×101 CFU/g of leaf tissue. In contrast, no viable bacteria were detected after 96 h at 15.5°C. Survival of P. ananatis on Florida pusley was also monitored during alternating 12-h wet and dry periods, or continuous wet or dry periods for 96 h at 15.5° or 21.1°C. Compared to initial or continuous dry periods, P. ananatis survived significantly better with a 12/12-h wet/dry cycle or a continuous 24-h wet period at both 15.5° and 21.1°C. Unlike at 15.5 ?C, P. ananatis populations (1.8×101 CFU/g) survived for 96 hours post inoculation at 21.1 ?C under a 12-h of dry/12-h wet cycle. These results demonstrate that P. ananatis can survive on Florida pusley leaves under conditions of 21.1°C and prolonged leaf wetness and may potentially serve as a source of inoculum to onion.