Identification of Resistance to Target Spot of Tomato Caused by Corynespora cassiicola in Wild Tomato Accessions

Tomato (Solanum lycopersicum) is an important vegetable crop and a valuable source of nutrients for the human diet. The southeast is the main fresh market tomato producer of the United States, with much of the production concentrated in Florida. However, production in this region is threatened by plant diseases such as target spot of tomato (TS) caused by Corynespora cassiicola, a multitrophic fungus widely distributed in tropical and subtropical areas. TS can infect foliage and fruit, often resulting in significant yield losses in conductive environments. There are no known TS-resistant cultivars, and control relies entirely on fungicidal sprays. However, several studies have demonstrated that the fungus is developing resistance to commonly used fungicides which further complicates disease management. The objective of this work was to identify sources of resistance to TS from wild Solanum accessions. Initial screens of 83 accessions informed the selection of 24 accessions for a more robust screening in which six diverse C. cassiicola isolates were used for single-isolate inoculation experiments. The results from a broad-sense mixed-model analysis including data from all six experiments demonstrated that all 24 accessions had significantly lower disease severities compared with the susceptible controls, suggesting that all accessions potentially harbor resistance quantitative trait loci (QTLs). Solanum cheesmaniae accession LA0524, S. galapagense accessions LA0483 and LA0532, and S. pimpinellifolium accession LA2093 were among the most resistant accessions tested and may be particularly useful for introgression of resistance into cultivated germplasm and for mapping of TS resistance QTLs.