Phylogenetic relationships among Cucumis species based on the ribosomal internal transcribed spacer sequence and microsatellite markers

Abstract

The phylogenetic relationships within the genus Cucumis (a total of 25 accessions belonging to 17 species) were studied using the nuclear ribosomal DNA internal transcribed spacer (ITS) region. The analysis included commercially important species such as melon (C. melo L.) and cucumber (C. sativus). Two additional cucurbit species, watermelon and zucchini, were also included as outgroups. The data obtained reflected the clustering of Cucumis species in four main groups, comprising accessions from cucumber, melon, C. metuliferus and the wild African species. Some of the species clustered in different positions from those reported in classifications previously described by other authors. The data obtained clearly identify a division between the 2n=2x = 14 species (C. sativus) and the 2n = 2x = 24 ones (C. melo and wild species). Within the wild species we identified a subgroup that included C. sagittatus and C. globosus. Oreosyce africana, also classified as Cucumis membranifolius, was shown to be nested within Cucumis. Three accessions previously classified as independent species were shown to be genotypes of Cucumis melo. A set of melon and cucumber SSRs were also used to analyse the Cucumis species and the results were compared with the ITS data. The differential amplification of the SSRs among the accessions made it possible to distinguish three main groups: melon, cucumber and the wild species, though with less detail than applying ITS. Some SSRs were shown to be specific for melon, but other SSRs were useful for producing PCR fragments in all species of the genus.