GENOMIC LOCALIZATION OF TOMATO GENES THAT CONTROL A HYPERSENSITIVE REACTION TO XANTHOMONAS-CAMPESTRIS PV VESICATORIA (DOIDGE) DYE

Xanthomonas campestris pv. vesicatoria causes bacterial spot, one of t he most serious diseases of tomatoes. The Lycopersicon esculentum acce ssion 'Hawaii 7998' is the only reliable source of resistance to race 1 strains of the pathogen. This resistance is associated with a hypers ensitive reaction controlled by multiple nondominant genes. The inocul ated area becomes fully necrotic 24 hr after inoculation in 'Hawaii 79 98,' whereas full necrosis is observed 5 and 4 days after inoculation in the susceptible species, pennellii (LA 716) and their F-1, respecti vely. An interspecific backcross population, using 'Hawaii 7998' as th e recurrent parent, was analyzed to determine the linkage relationship s between the resistance genes and 135 molecular marker loci. The rang e of responses of the BC, population included those of the parents. Li nkage to a hypersensitive response factor was assessed by comparing th e rates of necrosis development between homozygous and heterozygous pl ants at 8 hr-intervals. Three factors that affect the hypersensitive r esponse of 'Hawaii 7998' were detected. One factor is on the short arm of chromosome 1, another on the long arm of chromosome I, and a third on the long arm of chromosome 5. These factors appeared to act indepe ndently and to have additive effects.