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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 (Glycine max (L.) Merr.) seeds with undesirable texture cause processing complica- tions in soyfood production. Seed hardness is an important quality attribute for food-grade soy- beans. The objective of this study was to iden- tify quantitative trait loci (QTLs) associated with seed hardness in soybean. Three generations of F 2 -derived lines (159 F 2:3 , F 2:4 , and F 2:5 lines) from a soft ('SS-516') × hard ('Camp') soybean cross were grown in a replicated test in Fayetteville, AR, in 2003, 2004, and 2005. Pressure-cooked samples from each line were tested for seed hardness using a texture analyzer. A total of 874 simple sequence repeat (SSR) markers were used to screen the parents; 177 out of 236 poly- morphic markers between the parents showed polymorphism in the F 2:3 lines. A linkage map for seed hardness was established using 148 SSR markers, 15 of which were new and added to the current public soybean genetic linkage map. All identifi ed markers were placed on 19 linkage groups (LGs) and covered 1363.7 cM of the soy- bean genome with an average distance of 9.6 cM between markers. Broad-sense heritability was estimated to be 0.56 for seed hardness. Two stable QTLs across environments (Ha1 and Ha2, p < 0.00001) were identifi ed near Satt229 on LG L and Satt531 on LG D1a, respectively, for the average seed hardness over 3 yr. Ha1 had a logarithmic odds score of 6.17 with R 2 = 12.7%; Ha2 had a score of 5.08 with R 2 = 36.1%. A dom- inance-by-dominance interaction was detected between Ha1 and Ha2, explaining 7.9% of the phenotypic variance. Research is under way to confi rm the identifi ed QTLs for soybean seed hardness in multiple populations with different genetic backgrounds.

Soybean mosaic virus (SMV) is a highly destruc- tive viral disease. Three loci with 12 alleles con- ferring SMV resistance have been identifi ed in soybean (Glycine max (L.) Merr.). The objective of this study was to develop polymerase chain reaction-based markers for detecting the candi- date gene 3gG2 at the Rsv1 locus for SMV resis- tance in diverse soybean germplasm. A pair of DNA primers, Rsv1-f/r, was developed from the 3gG2 sequence. This primer pair produced a 341-bp DNA fragment specifi c for soybean cul- tivars containing Rsv1. The same fragment was confi rmed in genotypes containing Rsv1 alleles including 'Kwanggyo' (Rsv1-k), 'Marshall' (Rsv1- m), 'Ogden' (Rsv1-t), PI 96983 (Rsv1), PI 507389 (Rsv1-n), 'Raiden' (Rsv1-r), and 'Suweon 97' (Rsv1-s). The Rsv1-f/r fragment was also ampli- fi ed in genotypes with two-gene combinations (Rsv1Rsv3 and Rsv1Rsv4) but not in genotypes containing only Rsv3 or Rsv4 or in the sus- ceptible genotypes. The primer pair was used to screen for Rsv1 alleles in 97 SMV resistant genotypes. Results showed that 55 genotypes contained the 3gG2 gene, while 17 genotypes carrying the Rsv1-y allele and additional 25 SMV-resistant genotypes carrying Rsv3 or Rsv4 were not amplifi ed a product using the 3gG2 primer pair. Analysis of an F 2 population derived from J05 (Rsv1Rsv3) × 'Essex' (rsv1rsv3) showed a cosegregation between the marker Rsv1-f/r and the Rsv1 allele. Rsv1-f/r was also shown to be linked to simple sequence repeat marker Satt114 on soybean molecular linkage group F with a distance of 5.42 cM. This marker will give breeders a tool for marker-assisted selection and gene pyramiding in soybean breeding for SMV resistance.