Genetic and chemical polymorphisms of saponins in soybean seed.

The variation in saponin composition in soybean seeds is explained by different combinations of five genes controlling the utilization of soyasapogenol glycosides as substrates. The function of these genes is variety-specific and organ-specific. Phenotypes of over 1000 soybeans were classified into eight saponin types, and the frequency of phenotypes was different between the cultivated [Glycine max (L.) Merr.] and the wild soybean (G. soja Sieb. & Zucc.). The AaBc saponin type predominated in G. soja (58.4% of test collections), but was only found in 0.3% of G. max. Four unidentified arabinoside saponins were detected in the seeds of the AaBc type soybeans. The mode of inheritance of saponin types is explained by a combination of co-dominant, dominant and recessive acting genes. The combined chemical and genetic data show that the directed manipulation of soybean saponin composition is a possibility for the future.