Identification and inheritance of quantitative resistance against Verticillium dahliae in tomato

Verticillium dahliae is a soil-borne fungal pathogen that causes vascular wilt diseases in temperate regions around the world. The fungus can infect over 200 plant species, among which are many economically important crops. Yield losses caused by V. dahliae generally range from 10 to 15%, but for various crops, such as potato, cotton, lettuce and strawberry, yield losses of over 50% have been reported. For over a century, the identification and employment of genetic resistance has been one of the preferred strategies to control V. dahliae. This approach aims at the exploration of plant germplasm for resistance sources, identification of the underlying resistance genes or quantitative trait loci (QTLs), followed by the introduction of these genes or QTLs into commercial cultivars. In tomato, the only described qualitative resistances thus far against V. dahliae are the Ve1 gene and the dominantly inherited V2 locus. The aim of the research of this thesis was to identify additional genes or QTLs which provide resistance against V. dahliae. By using an optimized phenotyping method, several wild tomato accessions were identified which displayed broad-spectrum resistance against V. dahliae. Of one of these wild tomato accessions, QTLs were identified which caused a reduction in V. dahliae symptom expression.

We also investigated which  avirulence effector of V. dahliae isolates is recognized by the V2 resistance locus. By performing a comparative genomics analysis between isolates which are controlled by V2 and isolates which have overcome V2 resistance, we identified two candidate effector genes, one of which is most likely the avirulence effector recognized by V2.