Submitted to: Genetics
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/4/2003
Publication Date: 1/8/2004
Citation: Simko, I., Costanzo, S., Haynes, K., Christ,B., Jones, R.W. 2004. Linkage disequilibrium mapping of a Verticillium dahliae resistance quantitative trait locus in tetraploid potato (Solanum tuberosum) through a candidate gene approach. Theoretical and Applied Genetics. 108:217-224. Interpretive Summary: Verticillium wilt is a disease caused by the Verticillum fungus which survives in the soil and infects potato plants. Infected plants show premature yellowing of vines, wilting and eventually die. The disease is a limiting factor in many potato-producing areas, since most of the commercial cultivars are susceptible to infection. In tomato, which is genetically closely related to potato, two resistance genes were recently cloned. We have tested 139 potato cultivars and breeding selections grown in North America for resistance to Verticillium wilt. The association between resistance to the disease in potatoes and the presence of a molecular marker closely linked to the tomato resistance genes was found. This information will be used to develop new potato cultivars with improved resistance to the disease. Molecular markers can be used to screen for plants that are likely to be resistant and speed-up the selection process. Potato breeders, the potato industry, and consumers will benefit from this research.
Technical Abstract: We have used the linkage disequilibrium mapping method to test for an association between a candidate gene marker and resistance to Verticillium dahliae in tetraploid potato. A probe derived from the tomato Verticillium resistance gene (Ve1) identified homologous sequences (StVe1) in potato, which in a diploid population map to chromosome 9, in a position analogous to that of the tomato resistance gene. When a molecular marker closely linked (1.5 cM) to the homologues was used as a candidate gene marker on 135 tetraploid potato genotypes (mostly North American cultivars), the association between the marker and resistance was confirmed (p < 0.001). The amount of phenotypic variation in resistance explained by the allele of the STM1051 marker was greater than 10% and 25% in two subpopulations that were inferred from coancestry data matrix. Cloning of homologues from the highly resistant potato cv. Reddale indicates that the resistance QTL comprises at least an eleven-member family, encoding plant specific leucine rich repeat proteins highly similar to the tomato Ve genes. The sequence analysis shows that all homologues are uninterrupted open reading frames and thus represent putative functional resistance genes. This is the first time that the linkage disequilibrium method has been used to find an association between a resistance gene and a candidate gene marker in tetraploid potato. We have shown that it is possible to map QTL directly on already available potato cultivars, without developing a new mapping population.