Search

Salinity has been recognized as a constraint for soybean [Glycine max (L.) Merr.] production in many regions worldwide. Fortunately, genetic variation in salt tolerance is available in the soybean germplasm bank. However, current screening methodologies for salt-tolerant genotypes are time-consuming and often ineffective because of their limitations in detecting and measuring plant response to salinity. The objective of this study was to develop a rapid visual method for screening soybean genotypes in response to salt stress based on foliar symptoms. Soybean seedlings were grown in hydroponics with 0, 40, 80, 120, or 160 mM NaCl. Visual foliar symptoms of excessive NaCl were evident at 26 d after planting (14 d in 120 and 160 mM NaCl treatment). The NaCl level of 120 mM was most effective for salt-tolerance screening based on visual foliar symptoms on a group of differential genotypes. Chloride includers ('Williams', 'Clark', 'HBK R4924', and 'Dare') exhibited interveinal chlorosis, while CI excluders ('S-100', 'Lee 68', and 'HBK R5525') showed no chlorosis at the 120 mM NaCl level. At this critical selection level (120 mM NaCl), average leaf Na and [Cl.sup.-] contents were 2.64 and 1.96 times higher, respectively, for Cl includers than for Cl excluders. Plant damage was more evident at 120 and 160 mM NaCl, as demonstrated by the decreased shoot and root biomass and near maximum accumulation of Na and [Cl.sup.-] in the tissue. There was a significant and negative correlation (r = -0.69, p = 0.0006) between relative root dry weight and [Cl.sup.-] concentration in the leaf. This methodology is simple, rapid, and effective for selection of Cl tolerant genotypes with a minimum investment of cost and time.

Soybean [Glycine max (L.) Merr.] seeds with undesirable texture cause processing complications in soyfood production. Seed hardness is an important quality attribute for food-grade soybeans. The objective of this study was to identify quantitative trait Ioci (QTLs) associated with seed hardness in soybean. Three generations of [F.sub.2]-derived lines (159 [F.sub.2:3], [F.sub.2:4,] and [F.sub.2:5] lines) from a soft ('SS-516') x 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 polymorphic markers between the parents showed polymorphism in the [F.sub.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. AII identified markers were placed on 19 linkage groups (LGs) and covered 1363.7 cM of the soybean 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 identified near Satt229 on LG L and Satt531 on LG D1a, respectively, for the average seed hardness over 3 yr. Ha1 had a Iogarithmic odds score of 6.17 with [R.sup.2] = 12.7%; Ha2 had a score of 5.08 with [R.sup.2] = 36.1%. A dominance-by-dominance interaction was detected between Ha1 and Ha2, explaining 7.9% of the phenotypic variance. Research is under way to confirm the identified QTLs for soybean seed hardness in multiple populations with different genetic backgrounds.

Diversity of food-grade soybeans is critical for utilization of genetic resources in cultivar development, germplasm enhancement, and end-product commercialization. The objective of this study was to assess seed quality attributes and phenotypic variability among 54 U.S. and 51 Asian food-grade cultivars and breeding lines. The results showed greater genetic diversity of protein content, calcium content, seed hardness, and seed size uniformity than other quality traits in both small- and large-seeded genotypes evaluated in this study. Among the small-seeded soybeans, the U.S. genotypes were more diverse and exhibited higher swell ratio and oil content but lower stone seed ratio and protein content than Asian accessions. Among the large-seeded accessions, U.S. genotypes had higher stone seed ratio and oil content but lower swell ratio and protein content, and were less diverse than Asian genotypes. The characterization of diverse food-grade soybeans will facilitate parent selection in specialty soybean breeding. [ABSTRACT FROM AUTHOR]

Seed calcium content is an important quality attribute of specialty soybean [Glycine max (L.) Merr.] for soyfoods. However, analyzing seed for calcium content is time consuming and labor intensive. Knowing quantitative trait loci (QTL) for seed calcium will facilitate the development of elite cultivars with proper calcium content through marker-assisted selection (MAS). The objective of his study was to identify major QTL associated with calcium content in soybean seed. Calcium content was tested in 17 F2.3 and 157 F2.4 lines derived from the cross of SS-516 (low calcium) x Camp (high calcium). The F2.3 lines were genotyped with 148 simple sequence repeat markers in a previous study on seed hardness, and the genotypic data were used in the QTL analysis of the current study. Four QTL designated as Ca1, Ca2, Ca3, and Ca4 orp linkage groups (LGs) A2, 1, and M were identified by both single- marker analysis and composite-interval mapping, and the QTL accounted for 10.7%, I 6.3%, 14.9%, and 9.7% of calcium content variation, respectively. In addition, multiple- interval mapping analysis revealed a significant dominant-by- dominant interaction effect between Cal and Ca3, which accounted for 4.3% calcium content variation. These QTL will facilitate the implementation of MAS for calcium content in soybean-breeding programs. [ABSTRACT FROM AUTHOR]

Soybean [Glycine max (L.) Merr.] seeds with undesirable texture cause processing complications in soyfood production. Seed hardness is an important quality attribute for food-grade soybeans. The objective of this study was to identify quantitative trait loci (QTLs) associated with seed hardness in soybean. Three generations of F2-derived lines (159 F2:3, F2:4, and F2:5 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 polymorphic markers between the parents showed polymorphism in the F2:3 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 identified markers were placed on 19 linkage groups (LGs) and covered 1363.7 cM of the soybean 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 (Hal and Ha2, p < 0.00001) were identified near Satt229 on LG Land Satt531 on LG D1a, respectively, for the average seed hardness over 3 yr. Ha1 had a logarithmic odds score of 6.17 with R² = 12.7%; Ha² had a score of 5.08 with R² = 36.1%. A dominance-by-dominance interaction was detected between Ha1 and Ha2, explaining 7.9% of the phenotypic variance. Research is under way to confirm the identified QTLs for soybean seed hardness in multiple populations with different genetic backgrounds. [ABSTRACT FROM AUTHOR]