RESPONSE OF TOLERANT BREEDING LINES OF TOMATO, LYCOPERSICON-ESCULENTUM, ORIGINATING FROM 3 DIFFERENT SOURCES (LYCOPERSICON-PERUVIANUM, L-PIMPINELLIFOLIUM AND L-CHILENSE) TO EARLY CONTROLLED INOCULATION BY TOMATO YELLOW LEAF CURL VIRUS (TYLCV)

Selection of tomato plants supposedly tolerant to tomato yellow leaf c url virus (TYLCV), based solely on the absence of symptoms in an infes ted held can be misleading. An inoculation routine was therefore estab lished to avoid escapes and to overcome difficulties associated with t he age of the plant at the time of infection. The inoculation routine was applied to a selection of resistant/tolerant individuals generated through a diallel F-1 cross and to F-2 segregating populations origin ating from three wild tomato species described as tolerant to TYLCV: L ycopersicon peruvianum EC104395, Lycopersicon pimpinellifolium Hirsute and Lycopersicon chilense LA1969. Clear differences were observed bet ween susceptible symptomatic and tolerant symptomless tomato genotypes , indicating that the uncertainty resulting from escapes, from differe nt levels of inoculum, and from the time of inoculation, can be elimin ated. The genes involved in tolerance provided different levels of pro tection; combinations of various tolerant sources and levels in a sing le genotype gave a higher level of tolerance. Differences in level of protection were found between genes from the same source and between s ources; none of the sources tested had complete dominance. The results obtained with the F-2 segregating population showed that tolerance fr om L. pimpinellifolium is controlled by one major gene, that from L. c hilense by two genes, and that from L. peruvianum by three genes with no dominant effect. The combination of sources for resistance can thus have positive or negative synergistic effects, or no effect. We sugge st that a maximal level of tolerance can be obtained by the additive e ffect of the partly dominant genes from L. pimpinellifolium and L. chi lense.