Gene-For-Gene Relationships Specifying Disease Resistance in Xanthomonas campestris pv. vesicatoria – Pepper Interactions. G. V. Minsavage. Department of Plant Pathology, University of Florida, Gainesville 32611 U.S.A. D. Dahlbeck(2), M. C. Whalen (2), B. Kearney(2), U. Bonas(2,3), B. J. Staskawicz(2), and R. E. Stall(1). (1)Department of Plant Pathology, University of Florida, Gainesville 32611 U.S.A; (2)Department of Plant Pathology, University of California, Berkeley 94720 U.S.A; and (3)Institut für Genbiologische Forschung, Berlin, West Germany.. MPMI 3:41-47. Accepted 2 October 1989. Copyright 1990 The American Phytopathological Society.

Three groups of Xanthomonas campestris pv. vesicatoria strains were distinguished, based on the response to infection of the tomato cultivar Walter and a set of near-isogenic lines of pepper. The near-isogenic pepper lines were derived from Early Calwonder (ECW), ECW-10R, ECW-20R, and ECW-30R, and contain the resistance genes Bs1, Bs2, and Bs3, respectively. The XcvT group was avirulent on all pepper lines and virulent on Walter; the XcvP group was avirulent on specific pepper lines and also avirulent on Walter; and the XcvPT group was avirulent on specific pepper lines but virulent on Walter. To test whether avirulence genes played a role in these responses, genomic and plasmid DNA libraries were constructed from two strains of X. c. pv. vesicatoria. Three avirulence genes were identified that converted normally virulent strains to avirulence on specific lines of pepper. The three avirulence genes were characterized by restriction enzyme analysis, Southern blot analysis, and analysis of the phenotype of the hypersensitive reaction (HR). The avirulence gene avrBsT controlled the ability of the XcvT group to induce an HR on pepper. The avirulence genes avrBs2 and avrBs3 allowed strains carrying these genes to induce an HR on pepper lines containing the corresponding disease resistance genes Bs2 and Bs3. The avrBsT and avrBs3 genes were localized to indigenous plasmids while avrBs2 appears to be localized to the chromosome. To further characterize the HR resistance induced by X. c. pv. vesicatoria avirulence genes, four avirulence genes from X. c. pv. vesicatoria were conjugated into a spontaneous mutant of X. c. pv. vesicatoria that was virulent on all pepper lines. Comparisons of the electrolyte leakage patterns of resistant pepper lines inoculated with these transconjugants revealed that strains carrying the cloned avirulence genes induced patterns similar to those of the wild-type strains with that avirulence gene.