Identification of a New Begomovirus Resistance Locus, “Ty-6,” in Tomato

Begomoviruses, including Tomato Yellow Leaf Curl Virus (TYLCV), are among the most important diseases of tomatoes grown in tropical and sub-tropical regions of the world. The development of resistance to the begomoviruses TYLCV and to Tomato Mottle Virus (ToMoV) has been a major breeding objective of the University of Florida tomato breeding program since the early 1990s. Resistance has been incorporated from the cultivar Tyking and from several Solanum chilense accessions, and resistance alleles of the major resistance genes Ty-1 (and its allele, Ty-3), Ty-2, Ty-4, and ty-5 are all utilized in the program. The resistance in some advanced lines, however, is not explained by these alleles. Fla. 8383 has a moderate level of resistance derived from S. chilense accession LA2779, but lacks all of the previously identified resistance loci. In Spring 2010, 203 plants of an F₂ population derived from the cross between Fla. 8383 and the susceptible breeding line, Fla. 7776, were inoculated with TYLCV and evaluated for disease severity. Each plant was genotyped with 158 polymorphic snps developed through the SolCAP project. Single marker analysis identified a major resistance allele on chromosome 10, tentatively named “Ty-6,” which functions additively. For confirmation, Fla. 8638B, which has a high level of resistance conferred by ty-5 (derived from ‘Tyking’) and by one or more alleles derived from S. chilense accession LA1938, was crossed to the susceptible breeding line, Fla. 7804; 240 F₂ plants were inoculated with TYLCV and evaluated for disease severity in Fall 2012. Each plant was genotyped with a marker for the ty-5 allele and with a marker for the “Ty-6” allele. Both loci were highly significantly associated with resistance and together explained 73% of the phenotypic variation in the population. There was no epistatic interaction between ty-5 and “Ty-6”.