Relationships among wild relatives of the tomato, potato, and pepino

With ca. 200 species, the informally named Potato clade represents one of the larger subgroups of the estimated 1500 species of Solanum. Because its members include the potato (S. tuberosum), tomato (S. lycopersicum), and pepino (S. muri- catum), it is the most economically important clade in the genus. These crop species and their close relatives have been the focus of intensive research, but relationships among major lineages of the Potato clade remain poorly understood. In this study, we use sequences from the nuclear ITS and waxy (GBSSI), and plastid trnT-trnF and trnS-trnG to estimate a phylogeny and further explore relationships within the Potato clade. With increased sampling over past studies, the Potato clade emerges as a strongly supported clade and comprises 12-13 subclades which, for the most part, correspond to traditionally recognized sections. Solanum sect. Regmandra is sister to the rest of the lineages of the Potato clade which are, in turn, organized into two major subclades: (1) sections Anarrhichomenum, Articulatum, Basarthrum, Etuberosum, Juglandifolia, Lycopersicoides, Lycopersicon, and Petota, and (2) sections Herpystichum and Pteroidea. As in all other studies including these groups, sections Etuberosum, Juglandifolia, Lycopersicoides, Lycopersicon, and Petota form a strongly supported clade. Solanum oxycoccoides, a high-elevation species endemic to north-central Peru, was tentatively assigned to several groups within Solanum based on morphological evidence, but instead the species represents an independent lineage within the Potato clade, sister to the first major subclade. A key to the sections of the Potato clade is provided.