Molecular Characterization of a Tomato Cultivar Resistant to Bacterial Canker Disease Caused by Clavibacter michiganensis subsp. michiganensis

Bacterial canker disease in tomato is widely present worldwide and causes significant economic loss. The disease is caused by Clavibacter michiganensis subsp. michiganensis (Cmm), a Gram-positive plant-pathogenic bacterium and this pathogen is transmitted by seeds. When infected seeds are germinated, pathogens move to vascular system of tomato seedling. Typical disease symptoms such as wilting, maceration of stem tissues, and canker symptoms on stems and fruits appear in adult stages of tomato plants. So far only two quantitative trait loci (QTL) in Solanum habrochaites accession LA407 (previously named as Lycopersicon hirsutum) have been reported to confer disease resistance to Cmm. In this study, we aimed to find cultivars in the tomato species, S. lycopersicum, showing resistance to Cmm for future usage as resource of disease resistance. Based on breeding linages, we selected 12 commercialized cultivars and Moneymaker, which has been widely used as a susceptible cultivar. In addition, we used two different Cmm strains isolated from either tomato or pepper plants. Pathogenicity assay showed that (1) 11 out of 12 cultivars were highly susceptible to both strains and (2) one particular cultivar showed significant resistance phenotype to Cmm tomato strain, but extreme resistance phenotype to Cmm pepper strain, indicating that this cultivar may carry a disease resistance gene(s) against Cmm. In addition, molecular characterization of this cultivar at the genome level is being investigated.