The Sg-6 saponins, new components in wild soybean (Glycine soja Sieb. and Zucc.): polymorphism, geographical distribution and inheritance

Hypocotyl saponin composition of 1,198 accessions of wild soybean (Glycine soja) collected from China, Korea, Japan and Russia Far East was analyzed by thin-layer chromatography to determine polymorphic variation and geographical distribution. Eight common distinguishable saponin phenotypes were identified: Aa, Ab, AaBc, AbBc, Aa+α, Ab+α, AaBc+α and AbBc+α. The latter four +α type were new. All eight types were identified in China. Type Ab+α was absent in Korea. Types Ab+α and AbBc+α, and Aa+α and Ab+α were not identified in Japan and Russia far east, respectively. Six new triterpene saponins were detected in +α type via LC-PDA/MS/MS analyses. They were, tentatively, designated as H-αg, H-αa, I-αg, I-αa, J-αg and J-αa. These saponins were inherited together by a single dominant allele. A gene symbol Sg-6 was assigned. Hence, the new saponins were collectively named as Sg-6 saponins. The frequency of Sg-6 allele was 17.6 % in Chinese, 10.0 % in Korean and 1.0 % in Japanese wild soybean. The wild soybeans having Sg-6 saponins can be utilized in soybean breeding programs as well as in saponin biosynthesis studies in soybean.