statistically significant only if plants were inoculated through shoots. If inoculated through roots, the chromosome
seven locus was not significant.
Since these earlier studies were based on experiments with only one strain of P. solanacearum, an
important question was whether the partial resistance loci provided varying levels of resistance to different P.
solanacearum isolates. Therefore, cuttings from F2 plants in the mapping population were inoculated with two other
strains of the pathogen and the statistical significance for the resistance loci on chromosomes six and ten
estimated for each strain. All three strains were Race 1, with UW-364 coming originally from China (L. Sequiera, U.
Wisconsin) and the other two strains (PSS4 and PSS97) both coming from Taiwan (Jaw Feng, Asian Vegetable
Research and Development Center). Moreover UW-364 and PSS4 were both isolated from tomato, while PSS97
was isolated from eggplant.
The results (Table 1) clearly demonstrate that the partial resistance loci differ in their absolute and relative
impact on resistance depending on P. solanacearum strain. Specifically, the partial resistance locus on
chromosome six (near CT184) was highly dependent on P. solanacearum strain, showing the greatest resistance
to UW-364, but little resistance to PSS4 and only modest resistance against PSS97. By contrast, the partial
resistance locus on chromosome 10 (near TG225b and TG230) showed moderate levels of resistance to all three
strains, although its greatest effect was also observed with UW-364.
Literature Cited
Acosta, J. , Gilbert, J. , Quinon, V. 1964. Heritability of bacterial wilt resistance in tomato. Proc. Am. Soc. Hort. Sci.
84: 455-461.
Boucher, C. , Gough, C. , Arlat, M. 1992. Molecular genetics of pathogenicity determinants of Pseudomonas
solanacearum. Annu. Rev. Phytopathol. 30: 443-461.
Danesh, D., Aarons, S., McGill, G.E., Young, N. D. 1994. Genetic dissection of oligogenic resistance to bacterial
wilt in tomato. Molec. Plant-Microbe Interact. In press.
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