Morphological and Molecular Diversity in a Collection of the Andean Tree Tomato (Solanum betaceum Cav.)

Abstract

SUMMARY Tree tomato or tamarillo (Solanum betaceum Cav., syn. Cyphomandra betacea (Cav. Sendt.) is a small tree native to the Andean region that produces juicy berries the size of a hen’s egg. Tree tomatoes are commonly found in local markets of South America, where they are sold being consumed as a fresh fruit or for producing juices (Bohs, 1989). This species represents an important alternative to production, diversification and commercialization of non-traditional products and, in addition, it is a promising crop for some regions with Mediterranean climate (Prohens and Nuez, 2000). The expansion of the crop is limited by some factors, such as the lack of clear differentiation among varieties, low fruit quality (heterogeneity and phytosanitary problems), use of inappropriate varieties, or substitution of local varieties with materials from other origins; moreover, the tree tomato is frequently a subsistence crop and is considered a neglected crop, not included in programs of conservation and genetic improvement of genetic resources. This raises the need to undertake studies aimed at the characterization of its diversity, which is essential to its use and conservation, as up to now neither morphological descriptors for tree tomato characterization have been published, nor the morphological and genetic relationships among cultivar groups have been studied. We have made a morphological and molecular characterization of tree tomato including a significant number of morphological traits and AFLPs markers, based on a broad diversity of accessions (27 cultivated, collected in the Andean region -the center of origin of this speciesor in other continents, and belonging to S. cajanumense Kunth, used as an outgroup in the molecular characterization). Accessions were assigned to five cultivar groups: orange, orange pointed, purple, red, and red conical. As a result of our research we have elaborated a list of 39 quantitative morphological descriptors, useful to differentiate accessions and to identify characteristics of interest in accessions and cultivar groups (Acosta-Quezada et al., 2011). Statistical analyses performed have included measures of position and dispersion (mean, standard deviation and coefficient of variation), analyses of variance (to validate the utility of descriptors), and heritability. Statistically significant differences (P<0.05) among accessions were found for most traits, especially for fruit traits, which indicates that a wide variation exists and that it is possible to select materials with fruit characteristics more appropriate for the markets. Fruit traits have also displayed high heritability values, showing that selection for