Resistance against a Ralstonia solanacearum race 3-phylotype II strain JT516 was assessed in a F(2:3) and a population of inbred lines (RIL), both derived from a cross between L. esculentum cv. Hawaii 7996 (partially resistant) and L. pimpinellifolium WVa700 (susceptible). Resistance criteria used were the percentage of wilted plants to calculate the AUDPC value, and bacterial colonization scores in roots and stem (hypocotyl and epicotyl) assessed in two independent greenhouse experiments conducted during the cool and hot seasons in Réunion Island, France. Symptoms were more severe during the cool season trials. Heritability estimates in individual seasons ranged from 0.82 to 0.88, depending on resistance criterion. A set of 76 molecular markers was used for quantitative trait loci (QTL) mapping using the single- and composite- interval mapping methods, as well as ANOVA. Four QTLs, named Bwr- followed by a number indicating their map location, were identified. They explained from 3.2 to 29.8% of the phenotypic variation, depending on the resistance criterion and the season. A major QTL, Bwr-6, and a minor one, Bwr-3, were detected in each season for all resistance criteria. Both QTLs showed stronger effects in the hot season than in the cool one. Their role in resistance to R. solanacearum race 3-phylotype II was subsequently confirmed in the RIL population derived from the same cross. Two other QTLs, Bwr-4 and Bwr-8, with intermediate and minor effects, respectively, were only detected in the hot season, demonstrating that environmental factors may strongly influence the expression of resistance against the race 3-phylotype II strain JT516. These QTLs were compared with those detected in the RIL population against race 1-phylotype I strain JT519 as well as those detected in other previous studies in the same genetic background against other race 1-phylotype I and II strains. This comparison revealed the possible occurrence of some phylotype-specific resistance QTLs in Hawaii 7996.

Sources of resistance to tropical race 1 strains of Ralstonia solanacearum, the causative agent of bacterial wilt, have been identified in the tomato germplasm. Till now, no experimental data are available on Lycopersicon spp. (now Solanum spp.) sources for resistance to temperate race 3, biovar 2 strains. Eighty-two accessions belonging to different Lycopersicon spp. were evaluated for resistance to a race 3 strain endemic to Re´union Island. Evaluation was conducted in growth chambers, and included the Lycopersicon esculentum cv. Roma as susceptible control. No immunity or complete resistance was observed in any accession tested under our experimental conditions. Therefore, race 3 strain was demonstrated to be highly pathogenic on all the Lycopersicon accessions tested. Partial resistance was significantly detected in only one accession belonging to the species Lycopersicon peruvianum, and one L. esculentum var. cerasiforme tomato line. Five other genotypes from the species L. esculentum, Lycopersicon hirsutum and L. peruvianum were noteworthy. The Hawaii 7996 line represented the best source of partial resistance to race 3 with 52% of wilting. It can therefore be used as a starting point for introducing resistance to bacterial wilt caused by R. solanacearum race 3 in tomato and studying its genetic control.

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