Research Notes: Xanthomonas campestris pv. translucens Genes Determining Host-Specific Virulence and General Virulence on Cereals Identified by Tn5-gusA Insertion Mutagenesis. V. R. Waney. Plant Pathology Department, University of Florida, Gainesville 32611 U.S.A. M. T. Kingsley, and D. W. Gabriel. Plant Pathology Department, University of Florida, Gainesville 32611 U.S.A. MPMI 4:623-627. Accepted 27 June 1991. Copyright 1991 The American Phytopathological Society.

Transposon mutagenesis was used to obtain mutations affecting general and host-specific virulence in Xanthomonas campestris pv. translucens strain Xct-216.2. This strain causes bacterial leaf streak on barley, wheat, rye, oats, and triticale. Transposon Tn5-gusA inserted randomly into Xct-216.2 at a frequency of 10‾⁷-10?‾⁸ per recipient after conjugal transfer from Escherichia coli. Three thousand Tn5-gusA insertional derivatives were inoculated on the five hosts. Prototrophic mutants affected in virulence (growth and symptom induction) on one of the host species, and not the others (host-specific virulence minus phenotype, or Hsv‾) were identified at frequencies of 0.07% on barley (HsvB‾, 0.04% on wheat (HsvW‾), 0.11% on rye (HsvR‾), 0.07% on oats (HsvO‾), and 0.07% on triticale (HsvT‾). These mutants were not affected in their hypersensitive response on cotton, a nonhost. Prototrophic mutants affected in virulence on all hosts and failing to induce a nonhost hypersensitive response (Hrp‾ phenotype) were obtained at a frequency of 0.42%. Cosmid clones complementing one Hrp‾ mutant, and the HsvW‾ and HsvB‾ mutants were recovered from an Xct-216.2 wild type genomic library using the cloned Tn5::Xct-216.2 flanking DNA regions. The Xct-216.2 hrp clone hybridized to the hrp locus from Pseudomonas solanacearum strain GMI1000 cloned in pVir2 (C. A. Boucher, F. VanGijsegem, P. A. Barberis, M. Arlat, and C. Zischek, J. Bacteriol. 169:5626-5632). There was no evidence of avirulence or cultivar specificity of the hsv genes isolated from Xct-216.2 on 17 barley and 14 wheat cultivars tested. These hsv loci evidently represent a class of virulence genes distinct from hrp and avr loci, superimposed on a basic ability to parasitize.