Introgression of virus-resistance genes into traditional Spanish tomato cultivars (Solanum lycopersicum L.): Effects on yield and quality

The objective of this study was to determine and quantify the effects of ToMV, TSWV and TYLCV resistance introgressions (determined by Tm-2a, Sw-5 and Ty-1 genes, respectively) on the yield and quality of fresh market tomatoes. Two sets of near isogenic lines (NILs) containing the eight homozygous combinations for the three resistance genes were developed in the backgrounds of the traditional tomato cultivars 'De la Pera' and 'Muchamiel'. These NILs were grown and evaluated in replicated trials in five locations in south-eastern Spain. Across all the analyses performed, the chromosome fragment that consistently had a greater effect was that containing the Ty-1 gene, which conferred resistance to TYLCV. This gene introgression negatively affected all the studied parameters, except for soluble solids content, and its effect was particularly significant on total and commercial yields, which decreased by 50%. This reduction in agricultural yield would only be acceptable when cultivating under high levels of virus infection. The effects of the other introduced fragments (containing Tm-2a and Sw-5) were minor and more variable, increasing or decreasing depending on the trial and the studied parameter. Advanced breeding lines carrying ToMV and TSWV resistance genes in homozygous conditions can be developed without important losses in agronomic and quality characteristics. However, the Ty-1 gene used for TYLCV resistance should only be used in developing cultivars for highly virus-infected areas.