Inheritance and characterization of a null allele for group A acetyl saponins found in a mutant soybean (Glycine max (L.) Merrill)

A total of 801 cultivated soybean accessions and 330 wild soybean accessions were screened for genotypes lacking group A acetyl saponins in seed hypocotyls using thin layer chromatography and high performance liquid chromatography. Only one accession from the soybean cultivars, A-b(F) lacked group A acetyl saponins but it had an unknown saponin. The inheritance of a null allele for group A acetyl saponins in soybeans was determined by crosses between A-b(F) and Shirosennari, which had group A acetyl saponin Aa, and Suzuyutaka, which had group A acetyl saponin Ab, respectively. All F1 seeds from these crosses had Aa and Ab respectively. F2 seeds resulting from these crosses segregated 3:1 indicating that the absence of group A acetyl saponins is inherited as a simple recessive. The gene symbol sg-1 is assigned to the allele coding for the absence of group A acetyl saponins, Sg-1a for the presence of group A acetyl saponin Aa and Sg-1b for the presence of group A acetyl saponin Ab, respectively. Sg-1a and Sg-1b are codominant alleles. Through FAB-MS and chemical analyses, the unknown saponin accumulated in the seed hypocotyls of A-b(F), was assumed to be 3-O-[beta-D-glucopyranosyl-(1 to 2)-beta-D-galactopyranosyl-(1 to 2)-beta-D-glucuronopyranosyl]-22-O-[alpha-L-arabinopyranosyl] soyasapogenol A