Resistance of tomato line Hawaii7996 to Ralstonia solanacearum Pss4 in Taiwan is controlled mainly by a major strain-specific locus

Bacterial wilt caused by the soilborne bacterium Ralstonia solanacearum att acks hundreds of plant species, including many agriculturally important cro ps. Natural resistance to this disease has been found in some species and i s usually inherited as a polygenic trait, In tomato, a model crop plant, ge netic analysis previously revealed the involvement of several QTL (quantita tive trait loci) controlling resistance and, in all of these studies with d ifferent strains of the pathogen, loci on chromosome 6 played the predomina nt role in controlling this trait. Using quantitative data collected from a greenhouse test F-3 population, we identified a new locus on chromosome 12 that appears to be active specifically against a race 1 biovar 3 Pss4 bact erial strain endemic to Taiwan, Chromosome 6 still contributes significantl y to the control of the resistance, and weaker associations of the trait to other regions of the genome are observed. These results are discussed in t he contest of current molecular knowledge about the strain specificity of d isease resistance genes.