Genetic Variability of Seed Sugar Content in Worldwide Soybean Collections.

Soluble sugar is an important quality trait in soybean seed, especially in food grade soybeans. In this study, 241 plant introductions (PI) consisting of 3 maturity groups (MG) from 28 origins were investigated for their seed sugar content, including glucose, fructose, sucrose, raffinose, and stachyose. Significant variation was detected in individual and total sugars in soybeans from different origins and maturity groups. The PIs from the U.S. contained an average of 41.1 mg/g sucrose, significant lower than PIs (47.6 – 49.2 mg/g) from China, Japan, and South Korea, while other individual sugars were similar in PIs from all four countries. The PIs of MG 3 had higher concentration of individual and total sugars than MG 4, and followed by MG 5. Thirty PIs had significant high concentration of glucose and fructose as major seed sugar components, whereas the remaining PIs had sucrose as the major sugar. The glucose content ranged from 0.1 mg/g to 36.2 mg/g, and the fructose from 0.1 mg/g to 36.5 mg/g. The PIs from Nepal, Peru, and Turkey generally had higher glucose and fructose content (14.9 – 23.9 mg/g), but lower total sugars (74.6 – 78.8 mg/g). The sucrose content ranged from 1.6 mg/g to 95.4 mg/g, with the highest content detected in PI  91346 collected from China. The raffinose (0.1 – 19.9 mg/g) and stachyose (0.2 – 69.6 mg/g) constitute the unfavorable oligosaccharide content. Low oligosaccharide content was identified in PIs from different origins, with some PIs containing relatively high sucrose. Significant associations were found between each individual or total sugar. While the genetics and environmental effects need to be further investigated, the unique sugar PIs identified from this study will be useful for soybean breeding to improve seed quality and marketability.