SUMMARY The Center of Conservation and Improvement of Agrodiversity (COMAV) of the Polytechnical University of Valencia holds one of the most important collections of accessions of the genus Lycopersicon genus, including the cultivated tomato (Lycopersicon esculentum, L. esculentum var. cerasiforme) and its wild relatives (L. cheesmanii, L. pimpinellifolium, L. hirsutum, L. pennellii, L. chmilewskii, L. parviflorum L. peruvianum and L. chilense). In spite of tomato being one of the vegetables of greater economic importance at world-wide level, ambiguities in its taxonomy continue existing as well as doubts about its domesticación. In fact, intermediate forms are observed in many occasions between the cultivated tomato and the botanical variety cerasiforme, and between the cerasiforme form and L. pimpinellifolium. Also intermediate forms between L. pimpinellifolium and L. cheesmanii have been detected. These species constitute the Eulycopersicon subgenus, interfertile with the cultivated tomato. Of them, the botanical variety cerasifrome is considered as ancestry of the tomato and introgression phenomena between L. pimpinellifolium and the tomato have been reported. The theories regarding the domestication of the tomato are not unique, being the theories of Jenkins (1948) and Rick (1958) opposed to most recent ones of Rick and Fobes (1975) and Rick and Holle (1990). In order to contribute to the clarification of these aspects, in the present Doctoral Thesis the following objectives are proposed: 1.- Study of the morphologic and molecular variability of these species 2.- Elucidation of the phylogenetic relations between the species of the Eulycopersicon subgenus. 3.- Establishment of strategies of conservation of these species and in special of Lycopersicon pimpinellifolium, for which important differences in the degree of alogamy have been described. 4.- Beginning of the establishment of a core collection in the collection of accessions of L. pimpinellifolium of the COMAV. A total of 165 accessions of the Lycopersicon genus have been studied, belonging 48 of them to Lycopersicon esculentun var. cerasiforme, 86 to L. pimpinellifolium and 31 to L. esculentum. Experiments were carried out in 2000-01 and 2001-02 years during autumn-winter seasons. Morphological characterization was done following the tomato descriptors published by the IPGRI. AFLPs were used for molecular characterization. Data were analyzed by means of multivariant analysis, using Principal Components Analysis and Cluster Analysis. Euclidean distances were calculated for anlysis of quantitative data and the UPGMA clustering method was used. The robustness and level of reliability of clusters were fitted by bootstrap technique. ANOVA and Newman-Keuls test were performed. Genetic similarity between the different accessions were calculated. Polymorphism and the genetic diversity were calculated according to Nei (1973). The analysis of main components carried out allowed the assignment of most part of the accessions studied to Lycopersicon esculentum, L. pimpinellifolium and L. esculentum var. cerasiforme species. Nevertheless, the separation was not complete, existing a continuous gradation among them, probably as a result of a not finalized simpatric speciation process. The lack of identification of specific molecular markers of species support this hypothesis. The existence of interspecific hybridization would contribute to the maintenance of this situation, constituting L. esculentum, L. esculentum var. cerasiforme and L. pimpinellifolium extreme forms of this continuous. A series of specific qualitative characters of the most typical forms of the species in study was identified. Thus, the antocianic colour of the stem, the type of leaf "pimpinellifolium" (generally smaller, pinnate and with entire edges) and the style very projected were characteristic of L. pimpinellifolium. L. esculentum was characterized fundamentally by characters relative to the fruit, as the variation in the form and the color of the mature fruit, irregular forms of the cross-sectional section, the pistil scar and the apex of the fruit, all associated to the process of domesticación undergone by this species. var. cerasiforme was characterized by the absence of the typical characters of the two described species. The number of flowers per inflorescencia, the number and length of the petals and width and weight of the fruit, did not show interactions Accession x Year. These characters, along with the qualitative ones previously cited, are considered like as discriminants between L. pimpinellifolium, L. esculentum var. cerasiforme and L. esculentum. The cluster analysis carried out with morphological characters grouped L. pimpinellifolium accessions with those of var. cerasiforme, whereas the cluster made with molecular data grouped L. esculentum with var. cerasiforme, being L. pimpinellifolium separated of both. This supports the hypothesis that var. cerasiforme is the ancestry of the cultivated tomato. Accessions of L. pimpinellifolium displayed a high variability for vegetative, of flower and fruit characteristics contributing to demonstrate that L. pimpinellifolium, is a very variable species, against the uniformity previously established. Other studies made with these accessions have also demonstrated their variability for characteristics of quality and resistance to diseases, making it an extremely useful collection for tomato breeding. In the accesions studied in this work a gradation on the style exsertion is observed, associated to floral organs of greater size and greater degree of alogamy, being higher frequency of style very projected in the most northern Departments of Piura and Lambayeque, whereas in Cajamarca and La Libertad, abounds the entrances with styles nonprojected or even inserted. The populations from Piura and Lambayeque have a higher total genetic diversity, probably as a result of the higher degree of alogamia. This fact has important implications in the sampling and regeneration tasks in the Genebanks. Accessions of characterized L. esculentum var. cerasiforme have shown a high variability for morphologic characters, both vegetative and fruit. This variability was associated to the origin, being much more uniform and having characteristics of cerasiforme coming from Mexico, whereas those of Ecuador and other origins were much more variable, not corresponding sometimes to the typical form of this variety. Accessions of L. esculetum studied were grouped according to their origin, Mexico or Spain, regarding both for their morphologic and molecular characteristics. In the first case, it probably is due to the different exerted pressures of selection in both countries. In the second, it would be consequence of the geographic division of both groups for more than 500 years. Accessions from Mexico belong to “criollo” types, very appreciated by their characteristics of quality, resistance to cracking and the ability to fruits set at low temperatures. These accessions will be very useful for their use in breeding programs. The higher value of total genetic diversity for accession from Mexico, would support the existence of a bottle neck due to the limited number of individuals transported from Mexico to Spain, where the diffusion throughout Europe began. Three groups of accessions of L. pimpinellifolium have been established. One of them from the Galápagos Islands, other collected in Cuzco and the other from the North of Peru and Ecuador, with great morphologic and molecular differences. All of them will have to be represented in the core collection of this species at the Genebank of the COMAV. Cluster analisys allowed the identification of duplicated accessions in the collection. Duplicates appear grouped in the trees with considerably high bootstrap values. This information will allow the elimination of such duplicates for the formation of the core collection. The higher genetic diversity of the accessions from Piura and Lambayeque Departments as opposed to those of Cajamarca and La Libertad advises a greater representation of the formers in the nuclear collection, in order to assure that most of this genetic diversity is represented in the core collection.