Origin of T-type chloroplast DNA in potato

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Chioroplast DNA of the common potato is different from that of its immediate ancestor, the Andean tetrapiold cultivated potato, by the presence of a 241 bp deletion and named T-type chioroplast DNA. To explore the ancestral wild species that conferred T-type chioroplast DNA to the cultivated potatoes, 566 accessions of 35 wild species from Bolivia and Argentina were surveyed for the presence/absence of the deletion by a simple PCR-based assay. The deletion was found in 16 accessions of S, berthaulti, S.neorossli and S.tarijense. The sequencing analysis of the deleted region confirmed that the 241 bp deletion occurred in the same region. In addition to the presence/absence of the deletion, two PCR-RFLP markers (H2 and H3) and four microsatellite markers (NTCP6, NTCP7, NTCP1.4 and NTCP18) were used to evaluate S. berthaultii (30 accessions), S. neorossii (five accessions), S. tarijense (62 accessions), putative S. berthaultiix S. tarijense hybrids (25 accessions), S. tuberosum ssp. tubetosum (7 accessions mostly from Chile) and ssp. andigena (five accessions, all having T-type chioroplast DNA), and one accession from each of S. stenotomum, S. phureja and S. chacoense. Twenty-five haplotypes were distinguished. All of the S. tuberosum accessions having T-type chtoroplast DNA were distinguished as haplotype 1 holders. The haptotype 1 was also found in 14 accessions of S. tarijense and four accessions of S. berthaultiix S. tarijense hybids. This strongly suggests that the wild maternal ancestor of common potato was S. tarijense.