Reexamination of Series Relationships of Mexican and Central American Wild Potatoes (Solanum sect. Petota): Evidence from Chloroplast DNA Restriction Site Variation

Chloroplast DNA restriction analysis has been used to test the series classifications of the Mexican and Central American representatives of Solanum sect. Petota of Rydberg, Bukasov, Hawkes, and Correll. Three clades are supported: 1. all species in series Morelliformia, Pinnatisecta, and Polyadenia exclusive of S. bulbocastanum and S. cardiophyllum. Subclades within clade 1 include S. trifidum and S. tarnii; S. x michoacanum and S. pinnatisectum; S. brachistotrichum and S. stenophyllidium; S. clarum and S. morelliforme; and series Polyadenia; 2. S. bulbocastanum and S. cardiophyllum; 3. S. verrucosum (a Mexican diploid), the Mexican polyploid species, and the South American species. Within clade 3, series Conicibaccata forms a well-defined subclade, whereas S. verrucosum, series Longipedicellata, series Demissa, and the South American species form another. In reference to the latest classification of Hawkes, series Conicibaccata and Polyadenia are supported as monophyletic; the Mexican diploids are paraphyletic; and series Demissa, Longipedicellata, and S. verrucosum (series Tuberosa) form one monophyletic assemblage. Species within series Longipedicellata and Demissa are polyploid, possibly of hybrid origin, and may need less conservative markers or biparentally- inherited probes to distinguish them. These molecular results are compared to the diverse data sets that have led to this classification. Solanum sect. Petota Dumort., the potato and its wild relatives, traditionally has been consid- ered to be taxonomically difficult, and conflict- ing taxonomic interpretations of species bound- aries and series relationships are common. The group contains much morphological and phys- iological variability. An earlier taxonomic in- terpretation of the group (Correll 1962) recog- nized 157 species, while the latest (Hawkes 1990) recognizes 232 species. Bitter (1912) was the first to describe series in Solanum sect. Petota (series Conicibaccata and Maglia), although he failed to designate series affiliations for many species. Rydberg (1924) di- vided the Mexican and Central American po-