COMBINATIONS OF TY RESISTANCE GENES GENERALLY PROVIDE MORE EFFECTIVE CONTROL AGAINST BEGOMOVIRUSES THAN DO SINGLE GENES

Abstract

Begomoviruses are a major threat to tropical and subtropical tomato production, worldwide. Host resistance provides an effective strategy for reducing yield losses associated with these viruses. Resistance has been introgressed into cultivated tomato (Solanum lycopersicum L.) primarily from a number of wild tomato relatives, and the major resistance genes available to breeders today include Ty-1 (and its allele, Ty-3), Ty-2, Ty-4, ty-5, and a recently-identified gene tentatively named “Ty-6”. Important to the effective and efficient deployment of resistant cultivars is an understanding of each resistance allele’s effect when used alone and when combined with other resistance genes. Ty-1 and Ty2 are both dominant and, where effective, provide a high level of resistance; whereas the other genes provide partial resistance and are additive to partially dominant or recessive as with ty-5. Two- and three-gene combinations of Ty-3, Ty-4, and ty-5 in semi-isogenic backgrounds provided high levels of resistance to Tomato yellow leaf curl virus (TYLCV). Tomato mottle virus (ToMoV) trials in Florida using the same materials were severe, but indicated that Ty-3 and Ty-4 had small but significant effects in lowering ToMoV disease severity but, ty-5 did not. In two additional populations segregating for both ty-5 and “Ty-6” that were inoculated with ToMoV, ty-5 had no significant effect on resistance. Combining “Ty-6” and ty-5 homozygously provided a high level of resistance to TYLCV while the combination of homozygous ty-5 with heterozygous “Ty-6” was also good, but not as resistant as the former.