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.

Soybean mosaic virus (SMV) is one of the most prevalent viral diseases in all major soybean [Glycine max (L.) Merr.] growing areas worldwide, causing substantial yield losses and seed quality deterioration in soybean. Seven strain groups of SMV (G1–G7) in the United States and three resistance loci (Rsv1, Rsv3, and Rsv4) have been identified in soybean. The objective of this research was to screen diverse soybean germplasm in attempt to identify new alleles for SMV resistance. A total of 253 soybean accessions collected from 26 countries were screened with six SMV strains in the greenhouse. The results showed that 157 accessions were susceptible to all six tested SMV strains, 75 accessions were resistant to some of strains, while 21 accessions were resistant to all strains tested. Among the resistant accessions, seven showed complete resistance to six strains and presumably carried Rsv1‐h, Rsv4, or combinations of Rsv1, Rsv3, and Rsv4; 14 showed resistance or early seedling stage resistance to six strains and presumably carried the Rsv4 allele; 50 accessions exhibited similar reaction patterns to known alleles: two Rsv1, 22 Rsv1‐k, 16 Rsv1‐y, one Rsv1‐t, and nine Rsv3 Twenty‐five accessions showed distinct reaction patterns and presumably carry new alleles. The resistant accessions identified in this study will be valuable germplasm resources for breeding SMV resistance.

Purple seed stain (PSS), caused by Cercospora kikuchii, is a prevalent soybean disease that causes latent seed infection, seed decay, purple seed discoloration, and overall quality deterioration. The objective of this research was to screen soybean accessions from the United States Department of Agriculture germplasm collection for resistance to PSS. In total, 123 plant introductions (PI) from 28 different countries, representing maturity groups (MG) III, IV, and V, were screened. Incidence of Cercospora leaf blight (% CLB), visual PSS (% PSS), and seed infected by C. kikuchii (% C. kikuchii) in harvested seed were determined. In 2007, % C. kikuchii was 2 to 51% for MG III, 2 to 35% for MG IV, and 0 to 33% for MG V. In 2008, % C. kikuchii was 0 to 45% for MG III, 1 to 71% for MG IV, and 0 to 15% for MG V. In total, four and ten PI from MG III and IV, respectively, were identified as resistant to PSS in both years. Highly positive correlations were found for inoculated versus noninoculated treatments and for % PSS versus % C. kikuchii infection. The PSS-resistant PI identified in this study will be valuable to breeders in developing resistant cultivars.

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