SIMILAR YIELD REDUCTIONS UNDER DIFFERENT GROWING CONDITIONS CAUSED BY THE INTROGRESSION OF GENETIC RESISTANCE TO TYLCV INTO TRADITIONAL TOMATO CULTIVARS

We are conducting a breeding program to introgress resistance to several viral diseases (ToMV, TSWV, and TYLCV, the most relevant in south-eastern Spain) into Spanish traditional tomato cultivars. In order to determine the possible negative effect of the introduction of TYLCV resistance, 70 F₂ plants from the selfing of an advanced breeding line of the ‘Muchamiel’ cultivar, homozygous for the resistance alleles Tm-2a, Sw-5, and heterozygous for Ty-1 were evaluated for yield. Plants were grown under greenhouse in an autumn-winter cycle, at the Estación Experimental Agraria de Elche (IVIA), Elche (Alicante). Yields were relatively high for a traditional variety, since fruit weight was 5.2 kg/plant. The Aps-F₂ marker, linked to the Ty-1 gene was used to confirm that the genotypes in the F₂ population followed the expected ratios (¼:½:¼). Plants homozygous for the TYLCV resistance gene (genotype Ty-1/Ty-1) showed on average a 33% yield decrease with respect to the susceptible plants (genotype ty-1/ty-1), while the heterozygous plants (genotype Ty-1/ty-1) experimented only a 13% yield decrease. In a previous field experiment conducted under open air, in a different growing cycle (spring-winter) and in a lower yield environment (2.4 kg of fruit weight per plant), the percentages of yield reductions, 31% for the resistant homozygote and 8 for the heterozygote, were very similar to those determined in the present experiment.