Genetic basis of the lobedness degree in tomato fruit morphology.

Fruit shape is a key trait in tomato (Solanum lycopersicum L.). Since most studies focused on proximo-distal fruit morphology, we hypothesized that unknown QTLs for medio-lateral direction ones could be found analysing segregating populations where major shape genes are fixed. We examined the diversity of fruit morphology in medio-lateral direction; defined divergent traits in cultivars carrying identical genetic constitution at LC and FAS genes; and identified QTLs for lobedness degree (LD) by a QTL-seq approach. We found that LC and FAS genes were not enough to explain LD variability in a large tomato collection. Then, we derived F2 populations crossing cultivars divergent for LD where LC and FAS were fixed (Yellow Stuffer x Heinz 1439 [F2YSxH] and Voyage x Old Brooks [F2VxOB]). By QTL-seq we identified a QTL for LD on chromosome 8 in both F2, which was validated in F2YSxH by interval mapping accounting for ~ 17% of the variability. Other two QTLs located on chromosomes 6 and 11 with epistasis explained ~ 61% of the variability in the F2VxOB. In conclusion, three novel QTLs with major effect for LD (ld6, ld8, and ld11) were identified through the study of diversity and genetic segregation in intraspecific tomato crosses.

Tomato fruit quality traits and metabolite content are affected by reciprocal crosses and heterosis.

Heterosis occurs when the F1s outperform their parental lines for a trait. Reciprocal hybrids are obtained by changing the cross direction of parental genotypes. Both biological phenomena could affect the external and internal attributes of fleshy fruits. This work aimed to detect reciprocal effects and heterosis in tomato (Solanum lycopersicum) fruit quality traits and metabolite content. Twelve agronomic traits and 28 metabolites identified and estimated by 1H-NMR were evaluated in five cultivars grown in two environments. Given that the genotype component was more important than the phenotype, the traits were evaluated following a full diallel mating design among those cultivars, in a greenhouse. Hybrids showed a higher phenotypic diversity than parental lines. Interestingly, the metabolites, mainly amino acids, displayed more reciprocal effects and heterosis. Agronomic traits were more influenced by general combining ability (GCA) and metabolites by specific combining ability (SCA). Furthermore, the genetic distance between parental lines was not causally related to the occurrence of reciprocal effects or heterosis. Hybrids with heterosis and a high content of metabolites linked to tomato flavour and nutritious components were obtained. Our results highlight the impact of selecting a cultivar as male or female in a cross to enhance the variability of fruit attributes through hybrids as well as the possibility to exploit heterosis for fruit composition.