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Genetic Characterization of RRS1, a Recessive Locus in Arabidopsis thaliana that Confers Resistance to the Bacterial Soilborne Pathogen Ralstonia solanacearum

¹Laboratoire de Biologie Moléculaire des Relations Plantes-Microorganismes, CNRS-INRA, BP 27 Auzeville, Castanet-Tolosan, France; ²Department of Biological Sciences, Wye College, University of London, Wye, Kent, TN25 5AH, UK; ³Department of Plant Genetics and Biotechnology, Horticulture Research International, Wellesbourne, Warwick, CV35 9EF, UK

The soilborne, vascular pathogen Ralstonia solanacearum, the causative agent of bacterial wilt, was shown to infect a range of Arabidopsis thaliana accessions. The pathogen was capable of infecting the Col-5 accession in an hrp-dependent manner, following root inoculation. Elevated bacterial population levels were found in leaves of Col-5, 4 to 5 days after root inoculation by the GMI1000 strain. Bacteria were found predominantly in the xylem vessels and spread systemically throughout the plant. The Nd-1 accession of A. thaliana was resistant to the GMI1000 strain of R. solanacearum. Bacterial concentrations detected in leaves of Nd-1, inoculated with an hrp⁺ strain of R. solanacearum, were only slightly higher than those detected in the susceptible accession, Col-5, following inoculation with a strain whose hrp gene cluster was deleted. Leaf inoculation of the GMI1000 strain on the resistant accession Nd-1 induced the formation of lesions in the older leaves of the rosette whereas the same strain of R. solanacearum provoked complete wilting of Col-5. Resistance to strain GMI1000 of R. solanacearum segregated as a simply inherited recessive trait in a genetic cross between Col-5 and Nd-1. F₉ recombinant inbred lines generated between these two accessions were used to map a locus, RRS1, that was the major determinant of resistance between restriction fragment length polymorphism markers mi83 and mi61 on chromosome V. This region of the A. thaliana genome is known to contain many other pathogen recognition capabilities.

Additional keywords: hrp genes, R gene.