Development of a breeder-friendly functional codominant DNA marker for the I2 locus covering resistance to Fusarium oxysporum f. sp. lycopersici

Fusarium oxysporum f. sp. lycopersici Snyder & Hans. (FOL) is a major soil-borne pathogen and the causal agent of Fusarium wilt of tomato, resulting in significant production yield losses. Resistant cultivars have become the most effective method for controlling this fungal disease, and the most important resistance locus to F. oxysporum f. sp. lycopersici in tomato is I2, conferring resistance to race 2 of the pathogen, and widely used in breeding programs. Although this locus was cloned, a robust codominant DNA marker for the I2 locus is not available to date. The development of such a marker has been hindered by the presence of seven homologous sequences at this locus that tend to amplify, and by the absence of information about the structure of the recessive I2 locus. We performed a comparative analysis of the I2 locus nucleotide sequences of tomato genotypes resistant and susceptible to Fusarium wilt. We developed a breeder-friendly functional codominant cleaved amplified polymorphic sequence marker of I2 based on this analysis that can be used in tomato breeding programs for resistance to FOL race 2.