Chloroplast DNA analysis of Solanum bulbocastanum and S-cardiophyllum, and evidence for the distinctiveness of S-cardiophyllum subsp ehrenbergii (sect Petota)

Chloroplast DNA restriction site analysis was used to test hypotheses of sister group relationships of the diploid Mexican wild potato species Solanum bulbocastanum (ser. Bulbocastana) and S. cardiophyllum (ser. Pinnatisecta). A prior chloroplast DNA study including two accessions each of these two species supported them as sister taxa, widely separated from their presumed closest Mexican diploid species relatives. The present study samples more widely by examining 28 accessions of all three subspecies of S. bulbocastanum, and 20 accessions of all three subspecies of S. cardiophyllum. The results support two main clades exclusive of the outgroup: 1. Solanum bulbocastanum (all subspecies) and S. cardiophyllum (all subspecies except subsp. ehrenbergii), and 2. S. cardiophyllum subsp. ehrenbergii and members of ser. Pinnatisecta other than subsp. ehrenbergii. In the first dade, there was little resolution and some chloroplast types were shared by three subspecies of S. bulbocastanum and two subspecies of S. cardiophyllum. These results, in combination with an earlier chloroplast DNA study of the Mexican and Central American species, suggest that subsp. ehrenbergii is related to other members of ser Pinnatisecta, possibly S. brachistotrichum or S. stenophyllidium, or alternatively that subsp. ehrenbergii obtained the chloroplast genome of a species in ser. Pinnatisecta by introgression.