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Poster: Biology & Disease Mgmt: Bacteriology


Host range potential of bacterial soft rot pathogens isolated from Phalaenopsis and Oncidium orchids
R. CATING (1), B. Robinson (1), A. Palmateer (2), K. Frost (3) (1) Oregon State University, U.S.A.; (2) University of Florida, U.S.A.; (3) Oregon State University, U.S.A.

Bacteria from the genera Pectobacterium and Dickeya (formerly Erwinia chrysanthemi) are known to cause soft rot disease in many plant species. Since 2008, bacterial soft rot caused by a Dickeya sp. has been reported on several orchid genera in South Florida. Ten isolates (5 from Phalaenopsis, 5 from Oncidium) were identified as belonging to the Dickeya or Pectobacterium genera based on phenotypic and 16S sequence data and were cultured on nutrient agar for 24 h at 28°C. Cultures were suspended in sterile water and adjusted to a concentration of 1 x 108. Carrots, onions, potatoes (R. Burbank), and Phalaenopsis orchids were inoculated by placing a 10 µL drop of bacterial suspension directly over a wound made with a sterile pipette tip. Inoculated plant material was incubated at 28 °C and evaluated for symptoms at 24, 48, 72, and 96 h. Bacteria were re-isolated from symptomatic tissue and identified based on the 16S and Pel genes. Orchid isolates caused soft rot symptoms in onion, potato, carrot, and Phalaenopsis orchids. Recently, Dickeya spp. and a newly proposed species, D. solani, have been reported to cause soft rot disease of potato tubers in other parts of the world, and there is concern that new species will end up in the US. We are continuing work on the orchid strains to determine their appropriate species designation