DETECTION AND IDENTIFICATION OF PHYTOPATHOGENIC XANTHOMONAS STRAINS BY AMPLIFICATION OF DNA-SEQUENCES RELATED TO THE HRP GENES OF XANTHOMONAS-CAMPESTRIS PV VESICATORIA

Three pairs of oligonucleotide primers specific for different regions of the hrp gene (hypersensitive reaction and pathogenicity) cluster of Xanthomonas campestris pv. vesicatoria were designed and tested for a mplification of DNA isolated from a large number of different bacteria . DNA sequences related to the hrp genes were successfully amplified f rom X. fragariae and from 28 pathovars of X. campestris. No DNA amplif ication occurred with genomic DNA from phytopathogenic strains of X. c ampestris pv. secalis, X. campestris pv. translucens, and X. albilinea ns or from nonpathogenic opportunistic xanthomonads and phytopathogeni c strains of the genera Acidovorax, Agrobacterium, Clavibacter, Erwini a, Pseudomonas, and Xylella. The DNA from those bacteria also failed t o hybridize to hrp-specific fragments in Southern blot analysis. DNA f ragments amplified with a particular primer pair were of identical siz e from each of the different phytopathogenic xanthomonads. However, re striction analysis of these fragments by using frequently cutting endo nucleases revealed variation in the pattern for these hrp-related frag ments amplified from the different Xanthomonas strains. The restrictio n patterns generated for the different fragments allowed distinction o f the strains representing a pathovar or species of phytopathogenic xa nthomonads. We believe that DNA amplification with hrp-specific oligon ucleotide primers is a highly sensitive and specific method that can b e applied for detection and identification of phytopathogenic xanthomo nads.