Variation among tree tomato (Solanum betaceum Cav.) accessions from different cultivar groups: implications for conservation of genetic resources and breeding

Abstract

Tree tomato (Solanum betaceum, Solanaceae) is a neglected small tree native to the Andean region used for its edible and juicy fruits. We have elaborated a list of 39 quantitative morphological descriptors for different plant parts (plant architecture, leaf, inflorescence and flower, infructescence and fruit, and seed) and have used them to characterize 24 accessions of tree tomato from different origins corresponding to five cultivar groups: orange, orange pointed, purple, red, and red conical. Several parameters, including range, maximum/minimum value ratio, standard deviation, coefficient of variation, and broad-sense heritability, as well as analyses of variance, have been used to validate the utility of the descriptors, which have proved useful for the characterization of this crop. Significant (P < 0.05) differences among accessions were found for the descriptors we evaluated, with the exception of three flower-size descriptors. Fruit and infructescence traits and seed number displayed the most variation and greatest heritability values. Considerable variation was found within each cultivar group for many traits. Many differences were found at the morphological level between the odd, red conical group, which includes a single accession with small fruits containing very few seeds, and all other cultivar groups. Ranges of variation among these other groups overlap for most of the descriptors studied, although the orange and red cultivar groups are the most distinct. Most of the significant correlations found among traits connect descriptors from the same part of the plant. Multivariate cluster and principal component analyses separated the tree tomato accessions into several morphologically similar groups. With the exception of single accession clusters, the rest of clusters contain accessions of several cultivar groups, reflecting considerable variation within cultivar groups, as well as (with the exception of the red conical group) a low degree of morphological differentiation among them. The descriptors we developed and the results obtained are relevant for the conservation and breeding of this promising fruit crop.