Genetic variability of seed sugar content in worldwide soybean germplasm collections
Soluble sugar is an important quality trait in food-grade soybeans [Glycine max (L.) Merr.]. Desirable sugars such as sucrose, glucose, and fructose can help improve the taste and flavor of soyfood including tofu, soymilk, and natto; whereas oligosaccharides including raffinose and stachyose are indigestible by humans and animals and often cause flatulence or diarrhea. In this study, 241 plant introductions (PIs) of three maturity groups (MGs) from 28 origins were investigated for seed sugar content including glucose, fructose, sucrose, raffinose, and stachyose. Variation was detected in individual and total sugars in soybean PIs from different origins and MGs. Sucrose and stachyose are the major sugars in soybean seed. The sucrose content ranged from 1.6 to 95.4 mg g–1 with 13 PIs containing greater than 70 mg g–1 and 14 PIs having less than 10 mg g–1. The stachyose content ranged from 0.2 to 69.6 mg g–1 with 14 PIs containing less than 10 mg g–1 stachyose. The high sucrose and low stachyose types are the most valuable for breeding specialty soybeans for soyfood and animal feed. In addition, 30 PIs were identified as having high concentrations of glucose or fructose as major sugars. This new class of high glucose or fructose has not been reported before. While soybean germplasm with unique sugar profiles may be useful for future breeding and genetic research, environmental effects on sugar stability will need to be further investigated.