Cuchucho

BiochemicalSystematicsand Ecology,Vol. 14, No. 6, pp. 651-655, 1986. Printed in Great Britain.

0305-1978/86 $3.00+0.00 © 1986PergamonJournals Ltd.

Glycoalkaloids of SolanumSeries Megistacrolobumand Related Potato Cultigens
TIMOTHY JOHNS* and STANLEY F. OSMAN¢
Division of Biological Sciences, University of Michigan, Ann Arbor, MI 48109, U.S.A.; CEastern Regional Research Center, ARS,USDA, Philadelphia, PA 19118, U.S.A.

Key Word Index--Solanum Series Megistacrolobum; Solanum × ajanhuiri; Solanaceae; potato; Bolivia; glycoalkoloids;
domestication. Abstract--Glycoalkaloids were used as evidence of the affinities of nine taxa of Solanum Series Megistacrolobum and related potato cultigens from western Bolivia. S. boliviense, S. sanctae-rosae and S. toralapanum contain thecommertetraose sugar moiety and appear to represent a relatively wild group within the Series. S. megistacrolobum, S. sogarandinum and S. raphanifolium show anomolous glycoalkaloid profiles that probably reflect hybridization associated with human disturbance. Primitive forms of the S. × ajanhuiri cultigen are indistinguishable chemically from conspecific weeds that were previously classified as S.megistacroloburn. Variation in total glycoatkaloid content within Series Megistacrolobum likely reflects direct selection by humans for reduced glycoalkaloid levels during the domestication process.

Introduction

Solanum megistacrolobum Bitt. is among the
most frost-resistant potato species and is reputedly well adapted to arid conditions [1, 2]. The natural introgression of genes of S.megistacrolobum into the cultivated gene pool via the cultigen S. × ajanhuiri Juz. et Buk. has been important for extending the range of potato cultivation by Aymara-speaking farmers into the frigid and arid areas of western Bolivia. On the other hand populations of S. megistacrolobum have received genes from cultivated species through introgression; the nature of wild potatoes reflects humandisturbance associated with the domestication process [3, 4]. S. megistacrolobum, in particular, is a highly variable species [1, 5]. In general, discontinuities within the Series MegistacroIobum are difficult to delineate and make taxonomic decisions problematic. Surveys of steroidal glycoalkaloid constituents of wild species of tuber-bearing Solanum have neglected Series Megistacrolobum [6-8].Chemotaxonomic information was expected to given new insight into interspecific affinities
*Present address: Department of Entomological Sciences, University of California, Berkeley, CA 94720, U.S.A.

within the Series Megistacrolobum, as well as the origins of the cultigen, S. × ajanhuir~ The ready hybridization of S. megistacroIobum and the diploid cultigen S. stenotomum Juz. et Buk. indicates that S.megistacrolobum may have excellent potential in potato breeding. Assessment of glycoalkaloid content, in itself, is important for determining the suitability of wild species in breeding programs [9].
Results and Discussion Structural relationships of aglycones and glycoalkaloids identified in this study are recorded in Figure 1. Glycoalkaloid analyses of $. megistacrolobum (Table 1) areconsistent with the morphological variability typical of this species. Accessions obtained from the Potato Introduction Station, Sturgeon Bay, were characterized by tomatine (12), with some accessions also containing demissine (6) as either the major or minor constituent. Accession PI320303 contained commersonine (7), 6 and trace amounts of 12. It closely resembled PI458397, identified as S. toralapanumCard. et Hawkes, in both glycoalkaloid constituents and leaf morphology. Both collections were made in the southern part of the range of these species. Ochoa [10] has recently reduced S. toralapanum (referred to

(Received 14 August 1985)

651

652 ~ H

TIMOTHY JOHNS AND STANLEY F. OSMAN

RO 1 2 3 4 R R R R = = ~ = H; solanidine O-GIc-(l~3)-[Rha-(l~2)]-Gal; (x-solanine O-diRha-(l~2,...