Characterization of a repertoire of tomato fruit genetic variants in the San marzano genetic background

San Marzano (SM) is a worldwide famous tomato Italian traditional landrace characterized by elongated fruits with a dual-purpose use in the fresh and processing market. A repertoire of mutations affecting the fruit and of interest for commercial breeding were introduced into the SM genetic background following backcross schemes. The lines generated included 13 genotypes each carrying a single mutation in genes controlling a) the content of all pigments (hp-1, hp-2, pd), b) of carotenoids (r, t, at, B, B_moB), c) of chlorophyll (gf), d) of flavonoids (y) or e) the ripening process (Nr, rin, Gr). Five lines carrying a combination of two mutations were also included. Analysis of SNP polymorphisms showed that the genetic distance of the lines from the recurrent parent was very variable and not well predicted by the number of backcrosses because it was also a function of the dissimilarity of the donor parent. All the genotypes, together with an SM control, were grown in two consecutive years and characterized for vegetative, reproductive and fruit quality traits. Overall, the studied lines reproduced the SM typical phenotypes, but several differences also emerged as both possible negative or advantageous pleiotropic traits for fresh or processing uses and peeling. High pigment mutations confirmed the negative pleiotropic effects on plant fertility and fruit development described earlier and also negatively affected fruit post-harvest life. These latter defects were also reported in the carotenoid mutant tangerine. In contrast, absence of peel pigmentation in the y mutant was associated with positive postharvest properties as those fruit presented higher resistance to wrinkling and dehydration. Delayed ripening mutants showed positive post-harvest phenotypes, as expected. In conclusion, the study of the present repertoire of fruit variations in an elongated tomato genotype represents a contribution to expand the study of fruit physiology to unusual fruit types and to breed innovative tomato lines with valuable nutritional and technological properties.7s