Phylogenetic Relationships of Wild Potatoes, Solanum Series Conicibaccata (Sect. Petota)

Abstract

Solanum sect. Petota series Conicibaccata is a group of 40 wild potato species, composed of diploids, tetraploids, and hexaploids, distributed from central Mexico to central Bolivia. This study examined their species boundaries and interrelationships by phenetic analyses of morphological data and cladistic analyses of chloroplast DNA restriction site data. Mitotic chromosome counts were obtained for 114 accessions; species whose first counts are reported here are S. garcia-barrigae, S. orocense, and S. sucubunense. Most results were concordant in showing three main groups of species: 1) tetraploids and hexaploids from central Mexico to southern Ecuador; 2) diploids from northern Peru to Bolivia, included in a cpDNA clade of diploids and hexaploids assigned to ser. Demissa and ser. Tuberosa, and 3) diploids and tetraploids from southern Colombia to Peru, cladistically related to members of ser. Piurana. Some species boundaries, and even series boundaries of ser. Conicibaccata and ser. Piurana, are supported morphologically only by a combination of widely overlapping character states, none of which is constant for a species. Other species have no support, and it is likely that too many species are recognized in the group. The cladistic analysis of chloroplast DNA data suggested that some species represent a combination of apospecies and plesiospecies, and some populations are of possible hybrid origin. The genus Solanum L. contains about 1,000 to 1,100 species (D'Arcy 1991) and is one of the largest genera of angiosperms. Solanum sect. Petota Dumort., the potato and its wild relatives, includes 232 species as recognized by Hawkes (1990), or 223 species with the exclusion of nine nontuber-bearing species alternatively placed in sect. Etuberosum (Bukasov and Kameraz) A. Child, sect. Juglandifolium (Rydb.) A. Child, and sect. Lycopersicon (Mill.) Wettst. (Child 1990; Spooner et al. 1993). The tuber-bearing species are distributed from the southwestern United States to southern Chile, from sea level to over 4,500 m, with a concentration of diversity in the Andes. Section Petota contains diploids (2n = 2x = 24), tetraploids (2n = 4x = 48) and hexaploids (2n = 6x = 72), with occasional triploids and pentaploids. Section Petota is taxonomically difficult with much disagreement regarding species boundaries, affiliation of species to series, rank of infraspecific taxa, and hypotheses of hybridization (Spooner and van den Berg 1992a). Solanum ser. Conicibaccata Bitter presents many problems regarding species and series boundaries and is in need of revision. Bitter (1912) was the first to recognize series in sect. Petota. When Bitter (1912) first described the two series Conicibaccata and Maglia Bitter, the morphological distinction between the conical fruits of the former and rounded to ovoid fruits of the latter presented few taxonomic problems. As new species and series were described, these distinctions became imprecise and assignment of species to series varied widely among taxonomists, as summarized in Spooner and Sytsma (1992) and Spooner and van den Berg (1992a). The latest taxonomic treatment of sect. Petota (Hawkes 1990) recognized 19 tuber-bearing