Acridine Orange Selects for Deletion of hrp Genes in All Races of Pseudomonas solanacearum. Christian A. Boucher. Laboratoire de Biologie Moléculaire des Relations Plantes-Microorganismes, CNRS-INRA, BP 27, 31326 Castanet-Tolosan Cedex, France. Patrick A. Barberis, and Matthieu Arlat. Laboratoire de Biologie Moléculaire des Relations Plantes-Microorganismes, CNRS-INRA, BP 27, 31326 Castanet-Tolosan Cedex, France.. MPMI 1:282-288. Accepted 29 September 1988. Copyright 1988 The American Phytopathological Society.

Data previously established for Pseudomonas solanacearum strain GMI1000 concerning the structure of the genome in the vicinity of the cluster of hrp genes (Boucher et al. 1987, J. Bacteriol. 169:5626-5632) have been extended to 52 strains of P. solanacearum representing different races, biovars, and geographical origins. All pathogenic strains carry DNA sequences homologous to hrp genes present in strain GMI1000. For a majority of strains, as for strain GMI1000, acridine orange-resistant (Acr^{rhrp region in these mutants was deleted, causing a simultaneous loss of pathogenicity toward host and of the ability to induce a hypersensitive response on nonhost plants. In addition, they were auxotrophic for methionine and excreted a brown pigment, two phenotypic traits that had previously been shown to be associated in Acrr derivatives of strain GMI1000. These data collectively suggest a fairly similar organization of the hrp genes and the flanking DNA in this species. A restriction fragment length polymorphism study in the the hrp region and in three other randomly chosen regions shows the existence of a limited degree of polymorphism and suggests the coevolution of hrp genes with the rest of the genome.}