2017 ASHS Annual Conference

Fusarium wilt, caused by Fusarium oxysporum f. sp. lycopersici, (Fol) is a major soil-borne disease of tomato (Solanum lycopersicum) in many production regions throughout the world. Disease management is primarily achieved by the deployment of dominant, race-specific resistance genes. There are three races of Fol. Resistance to the third race (Fol3) is conferred by the I-3 gene originating from S. pennellii accession LA716. Although cultivars containing I-3 have been available since the mid 1990’s, the development and adoption of Fol3-resistant cultivars has been hampered due to the negative association of the I-3 locus with several horticultural traits. The S. pennellii species is reported to be highly resistant to all races of Fol, and it may harbor additional Fol3 resistance alleles. Based on the hypothesis that an alternative Fol3 resistance allele may have no such negative horticultural associations, we have sought to introgress novel Fol3 resistance into cultivated tomato. Seedling disease screens were employed for backcrossing resistance from 42 S. pennellii accessions into elite, Fol3-susceptible, backgrounds. Markers linked to I-3 were used to select against this locus at the BC₁F₁ generation, and selection for horticultural type was done at the BC₄F₁ generation. Progeny of single-plant selections corresponding to 32 of the original accessions were screened at the BC₄F₂ generation, and families from 18 different accessions segregated for resistance. Ratios of healthy to infected plants that approximated a 3:1 ratio (indicating the presence of a single, dominant resistance gene), and phylogenetic relationships among the 18 accessions, were considered in the selection of two BC₄F₂ families for genotyping. Results will allow mapping and subsequent characterization of novel resistance genes from these accessions.