An extreme cytoplasmic bottleneck in the modern European cultivated potato(Solanum tuberosum) is not reflected in decreased levels of nuclear diversity

We have used the polymorphic chloroplast (cp) and nuclear simple sequence r epeats (SSRs) to analyse levels of cytoplasmic and nuclear diversity in the gene pool of the European cultivated potato (Solanum tuberosum sap. tubero sum). Primers designed from the complete chloroplast sequence of tobacco (N icotiana tabacum) were used to amplify polymorphic products in a range of p otato cultivars. Combining the data from seven polymorphic cpSSR loci gave 26 haplotypes, one of which (haplotype A) accounted for 151 out of the 178 individuals studied and corresponded to the T-type cytoplasm previously ide ntified in cultivated potatoes using chloroplast restriction fragment lengt h polymorphism analysis. Phylogenetic and diversity analyses of the relatio nships between cpSSR haplotypes confirmed much higher levels of cytoplasmic diversity outwith the T-type group. Diversity levels at eight nuclear SSR loci, however, were not significantly different between cytoplasmic groups, suggesting a severe maternal bottleneck in the evolution of the modern cul tivated potato. These results highlight the importance in quantifying level s of cytoplasmic as well as nuclear diversity and confirm the need for a ch ange in breeding practices to increase levels of non-T-type cytoplasm in th e cultivated gene pool, thus helping reduce problems associated with pollen sterility. This may be facilitated by germplasm analysis using cpSSRs, whi ch will allow efficient selection of diverse cytoplasm donors.