Stacking multiple Tomato Yellow Leaf Curl Virus (TYLCV) resistance genes in tomato: Effect on Resistance and Fitness cost

Tomato production is in constant pressure of biotic and abiotic stresses that limit production. In South Texas, the main disease affecting production is caused by the Tomato yellow leaf curl virus (TYLCV), a virus vectored by the silverleaf whitefly (Bemisia tabaci). In the absence of Texas-adapted heat tolerant and TYLCV resistant cultivars, disease control relies on the application of insecticides to control the vector. Nevertheless, the excessive insecticide use has led to the loss of pesticide efficacy and ultimately to the severe decline of the tomato industry in the Rio Grande Valley since 2002. Up to now, six several major resistance genes have been identified and individually introgressed into Texas A&M tomato breeding lines. However, no-single Ty-resistance gene confers complete immunity. Preliminary data indicates that stacking more than one gene can provide optimal control even under high disease pressure. Therefore, more than one resistance gene needs to be introgressed into heat tolerant breeding lines in order to develop cultivars that perform well under harsh Texas conditions. Unfortunately, stacking several genes may also result on a fitness cost to the plant (e.g. yield reduction especially under low disease pressure). This proposed project aims to determine the best Ty- resistance gene combination(s) that optimize disease control while avoiding undesirable yield reduction due the cost of fitness. Furthermore, we will develop a high throughput method to genotype and phenotype TYLCV resistance.  Results from this project are fundamental to speed up the development of TYLCV resistant-high yield-heat tolerant cultivars adapted to Texas.