Quantitative Trait Loci Mapping of Seed Hardness in Soybean

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.