Genomic Localization of Tomato Genes That Control a Hypersensitive Reaction to Xanthomonas Campestris Pv. Vesicatoria (Doidge) Dye

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Xanthomonas campestris pv. vesicatoria causes bacterial spot, one of the most serious diseases of tomatoes. The Lycopersicon esculentum accession `Hawaii 7998' is the only reliable source of resistance to race 1 strains of the pathogen. This resistance is associated with a hypersensitive reaction controlled by multiple nondominant genes. The inoculated area becomes fully necrotic 24 hr after inoculation in `Hawaii 7998,' whereas full necrosis is observed 5 and 4 days after inoculation in the susceptible species L. pennellii (LA 716) and their F(1), respectively. An interspecific backcross population, using `Hawaii 7998' as the recurrent parent, was analyzed to determine the linkage relationships between the resistance genes and 135 molecular marker loci. The range of responses of the BC(1) population included those of the parents. Linkage to a hypersensitive response factor was assessed by comparing the rates of necrosis development between homozygous and heterozygous plants at 8 hr-intervals. Three factors that affect the hypersensitive response of `Hawaii 7998' were detected. One factor is on the short arm of chromosome 1, another on the long arm of chromosome 1, and a third on the long arm of chromosome 5. These factors appeared to act independently and to have additive effects.

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