Patterns of solanidine glycoalkaloid variation in four gene pools of the cultivated potato

Patterns of variation for the solanidine-based glycoalkaloids have been determined for tuber material of genebank accessions of landraces of the cultivated potato and three closely-related wild species. Total levels were low in the cultivated taxa investigated, S. phureja, S. stenotomum, and the tetraploid S. tuberosum in its two forms S. tuberosum ssp. tuberosum and S. tuberosum ssp. andigena. The only solanidine-based glycolkaloids found in the tubers investigated in this study were α-solanine and α-chaconine, with one additional related compound, dehydrocommersonine, found in tubers of an accession of S. canasense. The ratio of chaconine:solanine differed markedly from a mean of 0.98 in S. phureja to 2.28 in Chilean S. tuberosum ssp. tuberosum. The chaconine:solanine ratio was relatively constant within these two taxa, reflecting their relatively narrow genetic bases, but was much more variable within the taxa regarded as ancestral, S. stenotomum and S. tuberosum ssp. andigena. The wild species S. sparsipilum has been implicated in the origin of the tetraploid potato, S. tuberosum, but there was no support for this from the patterns of variation in chaconine:solanine ratio. The cline of chaconine:solanine ratios in cultivated potatoes along the spine of S. America does not appear to relate to the influence of local wild species through introgression, but may instead reflect differing selective pressures acting in different parts of the native range of the cultivated potato.