Sources of resistance to Verticillium dahliae races 1 and 2 in accessions of Solanum (section Lycopersicon)Verticillium wilt (Verticillium dahliae) is one of the most destructive diseases of tomato (Solanum lycopersicum). Two V. dahliae races have been described infecting tomatoes and both are present in Brazil. The most effective control strategy of V. dahliae race 1 isolates is based upon the use of resistant cultivars combined with cultural practices. However, there is so far no fresh-market tomato cultivar available with resistance to V. dahliae race 2. Therefore, it is important to identify new sources of effective resistance against both pathogen races. Solanum (section Lycopersicon) accessions were screened to search for resistance sources to both V. dahliae races 1 and 2. A germplasm collection composed by 100 accessions of cultivated and wild tomatoes was first inoculated via root dipping method (5 mL; 10(6) conidia/mL) with one isolate of V. dahliae race 1. Disease assessment was done 30 days after inoculation using a disease severity index ranging from 1 (plant without symptoms) to 5 (dead plant). Accessions with average severity index from 1 to 2 were classified as resistant. A subgroup of 38 race 1 resistant accessions was re-evaluated against four isolates of V. dahliae belonging to races 1 and 2. The cultivars Ponderosa and Floradade were used as controls. The assay was conducted under greenhouse conditions using a completely randomized, factorial (5 x 40) design with three replicates (three pots with four plants each). Evaluation was done based upon two epidemiological parameters: incubation period and disease severity index. Race-specific and multiple-race resistance sources were identified. The most promising accessions could be useful for breeding purposes aiming to develop cultivars with stable resistance to both races.
Solanum lycopersicum; resistance; genetic breeding
