Genomic Origins of Potato Polyploids: GBSSI Gene Sequencing Data

Chromosome pairing relationships within cultivated potato (Solanum tuberosum) and its wild tuber-bearing relatives (Solanum sect. Petota) have been interpreted by genome formulas, developed in the early 1900s, through techniques of classic meiotic analysis of interspecifi c hybrids. Here we reexamine potato genome hypotheses with the fi rst phylogenetic analysis of all major genomes of sect. Petota using cloned DNA sequences of the single-copy nuclear gene GBSSI (waxy). Our results provide the fi rst molecular confi rmation of allopolyploidy in wild potato. They both support prior hypotheses and identify novel genome origins never before proposed. The data will be useful to help design crossing strategies to incorporate wild species germplasm into cultivated potato. The cultivated potato, Solanum tuberosum, has about 190 wild species tuber-bearing relatives, forming a well-defi ned phylogenetic group, Solanum sect. Petota (Spooner and Salas, 2006). Th e wild species represent diverse gene pools that are of great importance in breeding resistant and heterotic genotypes. However, not more than 10% of them are currently involved in the breeding process (Ross, 1986). A better understanding of their genome relationships would clarify the prospects for introgression of alien genes into potato and will help in planning eff ective breeding programs. About 70% of these wild species are diploid at 2n = 2x = 24, with the remaining species polyploid, mostly at the tetraploid (2n = 4x = 48) or hexaploid (2n = 6x = 72) levels. Th ese polyploids are valuable sources of genes for disease resistance, stress tolerance, and improved tuber quality in potato. For example, S. demissum is a source of late blight (Phytophthora infestans) resistance and has been incorporated into potato cultivars (Plaisted and Hoopes, 1989). Solanum acaule is a source of frost tolerance (Vega et al., 2000), and S. hjertingii is resistant to bruising (Culley et al., 2002). Other Solanum allopolyploids contain genes for resistance to soft rot (Pectobacterium spp.), bacterial ring rot (Clavibacter michiganensis subsp. sepedonicus), potato leafroll virus, potato virus X, and potato virus Y (Jansky, 2000). D.M. Spooner, F. Rodríguez, and S.H. Jansky, USDA-ARS, Dep. of Horticulture, University of Wisconsin, 1575 Linden Dr., Madison, WI 53706-1590; Z. Polgár, University of Pannonia, Center of Agricultural Sciences, Potato Research Centre, 8360 Keszthely, Deak F. u. 16., Hungary; H.E. Ballard, Jr., Dep. of Environmental and Plant Biology, Ohio University, 317 Porter Hall, Athens, OH 45701-2979. Received 11 Sept. 2007. *Corresponding author ([email protected]). Published in Crop Sci. 48(S1) S27–S36. Published 8 Feb. 2008. doi:10.2135/cropsci2007.09.0504tpg © Crop Science Society of America 677 S. Segoe Rd., Madison, WI 53711 USA Abbreviations: AFLP, amplifi ed fragment length polymorphism; EBN, endosperm balance number; MP, maximum parsimony. Ge ome The