Taxonomy of Mexican diploid wild potato (Solanum sect. Petota) species: A morphological and molecular study

The potato and its wild relatives (Solarium sect. Petota) are distributed from the southern United States, throughout Mexico and Central America, continuing throughout the Andes to northern Argentina and adjacent Chile. About 30 of the approximately 200 wild members of sect. Petota occur in the United States, Mexico and Central America. Some of these 30 species are difficult to differentiate based on morphology. A prior chloroplast DNA restriction site analysis of these 30 species showed that 13 of them formed a clade consisting only of diploid species, but there was low resolution within this clade. The objective of this thesis was to better resolve species boundaries of the Mexican Stellata, investigate their relationships, and test a biogeographic hypothesis involving putatively related species in South America. A thorough morphological study was conducted, and two nuclear molecular markers, microsatellites and Amplified Fragment Length Polymorphisms (AFLPs) were used.; The morphological study resolved most of the problematic species, except a few like S. brachistotrichum, S. cardiophyllum subsp. ehrenbergii, and S. stenophyllidium that were hard to distinguish. Microsatellites were an inappropriate phylogenetic marker, as they showed poor to no support for these species. I showed this was caused by a cross-species amplification problem, since the microsatellite primers were developed for cultivated potato, S. tuberosum. After sequencing three microsatellites and comparing them to S. tuberosum , I found divergence of priming sites and divergence of microsatellite flanking sequences showing non-homology of microsatellite fragment sizes in the Mexican species relative to S. tuberosum.; AFLPs are becoming widely used, including in potato. After converting the AFLP data obtained through fluorescence into a presence/absence data set, I analyzed them phenetically and cladistically. Results of both techniques were similar, but some significant differences were found. Using AFLPs, most of the species are supported, except S. brachistotrichum, S. cardiophyllum subsp. ehrenbergii, and S. stenophyllidium , which are intermixed, as in the morphological study. The previously hypothesized close relationship between the primitive Mexican and South American Stellata species was supported. These results will be used in an ongoing taxonomic monograph of the wild potatoes from the United States, Mexico, and Central America.