Comparative differentiation in mitochondrial and chloroplast DNA among cultivated potatoes and closely related wild species

A total of 476 accessions of seven cultivated and 32 wild potato species previously characterized by nuclear DNA (nDNA) and chloroplast DNA (ctDNA) marker analyses were employed to the mitochondrial DNA (mtDNA) marker analysis. Fourteen simple sequence repeat (SSR) markers with mononucleotide repeat regions were developed from the potato mtDNA, although their variability was extremely low. Six mtDNA markers including three developed SSR markers disclosed 40 banding patterns that discriminated 63 different mtDNAs. For the same set of samples, 72 ctDNA banding patterns discriminated 129 different ctDNAs. Consequently, 164 haplotypes were distinguished. The correlation between ctDNA and mtDNA differentiation was positive (r = 0.226), but poor when compared with that between ctDNA and nDNA (r = 0.415), which likely lowered the utility of mtDNA polymorphisms in evaluating relationships among these species. Nevertheless, a finding of a unique mtDNA type in all T-type ctDNA holders (S. tuberosum and S. tarijense) strongly supports S. tarijense functioned as a maternal ancestor of potato.