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Genetics

Mutations for Change of Race in Cultures of Xanthomonas vesicatoria. D. Dahlbeck, Graduate research assistant, Plant Pathology Department, University of Florida, Gainesville 32611, USA; R. E. Stall, professor, Plant Pathology Department, University of Florida, Gainesville 32611, USA. Phytopathology 69:634-636. Accepted for publication 21 December 1978. Copyright 1979 The American Phytopathological Society. DOI: 10.1094/Phyto-69-634.

Suspensions of Xanthomonas vesicatoria at approximately 10⁴ cells per milliliter were infiltrated into the mesophyll of pepper (Capsicum annuum) leaves that reacted hypersensitively to the bacterium. Mutants in the inoculum produced lesions after 3–4 wk of incubation and bacteria from those lesions produced a susceptible reaction in the leaves. With fluctuation analysis experiments it was determined that these mutations occurred randomly in nutrient broth cultures at an apparent rate of 4 × 10^–4 mutants per cell per division. Within the populations of X. vesicatoria mutations occurred that converted the tomato race 1 to pepper race 2 and pepper race 2 to pepper race 1. No mutational conversion was observed from tomato race 1 to pepper race 1. It was postulated that the latter only would occur after a double mutation. The high rate of mutation for change of race did not occur with change in resistance to streptomycin. The latter occurred at an apparent rate of 1.9 × 10^–9 mutants per cell per division.