Molecular mapping of hypersensitive resistance from tomato 'Hawaii 7981' to Xanthomonas perforans race T3.

Bacterial spot of tomato (Solanum lycopersicum) is caused by four species of Xanthomonas. The disease causes significant yield losses and a reduction in fruit quality. Physiological races have been described with tomato race 3 (T3) corresponding to strains of Xanthomonas perforans. The breeding line Hawaii 7981 (hereafter H7981) shows a hypersensitive reaction (HR) to race T3 strains conditioned by the interaction of the host resistance locus Xv3 and the bacterial effector avrXv3. The Xv3 gene is required for H7981-derived resistance to be effective under field conditions, though its expression is subject to genetic background. The segregation of HR in F(2) populations derived from H7981 crossed to processing tomato parents OH88119 and OH7870 was studied in 331 progeny, with the two independent crosses providing validation. We screened 453 simple-sequence repeat, insertion/deletion, and single-nucleotide polymorphism markers and identified 44 polymorphic markers each for the OH88119 and OH7870 populations covering 84.6 and 73.3% of the genome, respectively, within 20 centimorgans (cM). Marker-trait analysis using all polymorphic markers demonstrated that Xv3-mediated resistance maps to chromosome 11 in the two independent crosses. Allelism tests were conducted in crosses between lines carrying Xv3 derived from H7981, Rx-4 derived from plant introduction (PI) 128216, and resistance derived from PI 126932. These allelism tests suggested that the loci conditioning HR to race T3 strains are linked within 0.1 cM, are allelic, or are the same gene.