Accession S. peruvianum PI 126944 has been reported as resistant to several biotic stresses, among them to Tomato yellow leaf curl disease, (TYLCD). In previous works carried out in the "Instituto Universitario para la Conservación y Mejora de la Agrodiversidad Valenciana" (COMAV) three interspecific hybrids between this accession and cultivated tomato were obtained, using immature seeds rescue. In subsequent works more advances generations from these materials were developed, including until the pseudo-F6 generations and backcrosses to the cultivated species of some of the pseudo-Fn generations. With the aim of taking advantage of these materials in the improvement of cultivated tomato, in previous works of the group, the development of a set of Introgression lines (ILs) that contain the genome of the accession PI 126944 in the genetic background of S. lycopersicum was initiated. The obtaining of a large number of descendants is necessary in order to have correctly represented the genome of the donor species, thus there is the need to optimize the protocols In this sense, the first aim of this work was the study of several factors involved in the overcoming of the incompatibility barriers, to obtain a high number of descendants and maximize the probability of introgressing the genome of PI 126944 in the set of ILs. Three backcross assays were carried out, initiated with different plants of the generations pseudo-F4, pseudo-F5 and pseudo-F6. The parental genotype resulted a determinant factor in the obtaining of descendants, so the recommendation is the use of the maximum number of different genotypes, in order to maximize the probability of obtaining progeny. A proof of different culture media was carried out, which allowed the selection of the better combination of auxins and cytokinins to grow immature seed and regenerate plants. The effect of the number of days from pollination to fruit harvest was also studied. As mentioned before, the collection of ILs results of interest, given the resistance of the donor parental to TYLCD, among others traits. Once the collection is completed, it will be evaluated for its resistance to this disease. The previous studies showed that it is probably a quantitative resistance, whose expression is often more dependent of the environmental conditions and of other factors. In these cases, the use of only one resistant and one susceptible control is not sufficient to determine with accuracy the level of resistance. Availability of controls with different levels of resistance would allow a more precise phenotyping. A group of researchers of the "Volcani Center" developed a scale that consisted of seven lines with different levels of resistance to TYLCD, introgressed from different wild species. In this work, the response of this scale in seven distinct assays was evaluated, four of them carried out in the COMAV-UPV and the others three in the "Instituto Nacional de Ciencias Hortícolas de Cuba". Two isolates of TYLCV (Tomato yellow leaf curl virus), one of the species causing TYLCD, different inoculation method, two development stages of the plant and several environmental conditions were evaluated. In general, the symptoms were more slight that the obtained in the conditions assayed by the authors that developed the scale, although the order of the lines in the scale were maintained, with few exceptions. However, in most of the conditions, the response obtained did not correspond to a graded scale, since there were high differences among the symptom scores of the susceptible and the resistant lines, with very small the differences among the resistant lines. These results suggest the possibility to reduce the number of lines to employ in each concrete condition, selecting the most susceptible, the most resistant and another with intermediate levels of resistance. TESIS