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Etiology

Association of Pseudomonas syringae pv. syringae With a Leaf Spot Disease of Tomato Transplants in Southern Georgia. J. B. Jones, Postdoctoral associate, Department of Plant Pathology, University of Georgia, Athens 30602; S. M. McCarter(2), and R. D. Gitaitis(3). (2)Professor, Department of Plant Pathology, University of Georgia, Athens 30602; (3)Assistant professor, Coastal Plain Experiment Station, Tifton, GA 31793. Phytopathology 71:1281-1285. Accepted for publication 2 April 1981. Copyright 1981 The American Phytopathological Society. DOI: 10.1094/Phyto-71-1281.

An outbreak of a foliar disease on tomato transplants in southern Georgia during 1980 was originally diagnosed as bacterial speck caused by Pseudomonas tomato (P. syringae pv. tomato). Isolates from diseased tissue yielded a green fluorescent pseudomonad that was oxidase- and arginine dihydrolase-negative and induced a hypersensitive reaction in tobacco but, in pathogenicity tests, did not cause typical bacterial speck symptoms. Physiological, biochemical, and pathogenicity tests demonstrated that the 1980 Georgia isolates were more similar to P. syringae (P. syringae pv. syringae) than to P. tomato. Most isolates of the new bacterium were similar to P. syringae in producing syringomycin, in using erythritoal and dl-lactate as substrates, and in forming ice nuclei. The 1980 isolates typically caused necrotic leaf spots with halos on California Blackeye 3 cowpea and necrotic reactions on Lovell peach, both known hosts of P. syringae, whereas P. tomato isolates usually caused no necrotic symptoms. The new bacterium also caused brown necrotic lesions without halos on leaves of Chico III tomato plants after infiltration with the bacteria or when wounds were made. These results show a fluorescent pseudomonad other than P. tomato may be responsible for necrotic lesions on tomato transplants and indicate the need for additional testing to differentiate the bacteria during certification procedures.