QTL MAPPING OF FOLIAR GLYCOALKALOID AGLYCONES IN SOLANUM-TUBEROSUM X SOLANUM-BERTHAULTII POTATO PROGENIES - QUANTITATIVE VARIATION AND PLANT SECONDARY METABOLISM

Glycoalkaloids are quantitatively inherited in Solanum, and in high co ncentrations they can be toxic to humans. The increased use of wild po tato germplasm to improve the pest resistance, yield, and quality char acteristics of cultivated potato may elevate or introduce new, more to xic glycoalkaloids into the cultivated gene pool. Therefore, it is imp ortant to increase our understanding of their inheritance, accumulatio n, and biosynthesis. Glycoalkaloids have two basic constituents - a gl ycosidic grouping and a steroid alkaloid skeleton. Steroid alkaloids a re classified as solanidanes and spirosolanes, of which solanidine and solasodine are, respectively, representatives. RFLP-mapped, diploid, reciprocal backcross potato progenies involving the parents S. tuberos um and S. berthaultii, which produce solanidine and solasodine, respec tively, were analyzed for segregation of the glycoalkaloids solanine, chaconine, solasodine and solamargine to identify quantitative trait l oci (QTLs) for the production of the aglycones solanidine and solasodi ne. The F-1 clone M200-30 exhibited low to nondetectable levels of sol asodine and solanidine, suggesting that expression was controlled by r ecessive genes. In a backcross to berthaultii (BCB) and backcross to t uberosum (BCT), several QTLs for the accumulation of solasodine and so lanidine were identified. Three QTLs explaining approximately 20% of t he variation in solasodine were identified in BCB on chromosomes 4, 6, and 12. Similarly, three QTLs were identified in BCT on chromosomes 4 , 8 and 11, but these accounted for only 10% of the variation observed in solasodine accumulation. Two QTLs for solanidine were identified i n BCT on chromosomes 1 and 4. The QTL located on chromosome 1 was high ly significant, accounting for 17% and 22% of the variation in solanid ine accumulation in 1994 and 1995, respectively. This same QTL was als o detected in BCB. The QTLs detected in this study probably represent structural and/or regulatory genes controlling the accumulation of sol asodine and solanidine. Results are discussed in the context of steroi d alkaloid accumulation and biosynthesis.