The value of soybean [Glycine max (L.) Merr.] depends on quantity (yield) and quality, such as seed composition and test weight (TW). Test weight is a bulk density measurement for grain quality evaluation, and higher TW grains are preferred for storage, transport, and export. Thus, soybean breeding should focus on improvement of TW. The objectives of this study were to determine genotypic and environmental effects on TW of soybean and explore relationships of TW with yield, maturity, 100 seed weight (SDWT), seed quality (SQ), seed oil concentration (SOC), and seed protein concentration (SPC). Three sets of breeding populations (BPs), two mapping populations (MPs), and five different high vs. low seed protein near-isogenic lines populations (NILPs) were used. The BPs and MPs had an average range of 3.5 kg hectoliter (hL) -1 in TW among genotypes. The average ranges of TW in the NILPs were equal for both low protein (LP) and high protein (HP) lines (2.7 kg hL -1 ). Broad-sense heritability estimates for TW ranged from .62 to .95. The genotypic and G × E effects on TW were significant in all trials. The SDWT, SQ, SOC, and SPC had strong significant relationships with TW in multiple trials, but were inconsistent overall. Test weight of NILPs differing by presence of 'Danbaekkong' high protein allele on chromosome 20 had mostly significant positive and negative relationships with SPC and SOC, respectively.This is an open access article under the terms of the Creative Commons Attribution-NonCommercial-NoDerivs License, which permits use and distribution in any medium, provided the original work is properly cited, the use is non-commercial and no modifications or adaptations are made.

Trypsin inhibitors (TI), a common anti-nutritional factor in soybean, prevent animals’ protein digestibility reducing animal growth performance. No commercial soybean cultivars with low or null concentration of TI are available. The availability of a high throughput genotyping assay will be beneficial to incorporate the low TI trait into elite breeding lines. The aim of this study is to develop and validate a breeder friendly Kompetitive Allele Specific PCR (KASP) assay linked to low Kunitz trypsin inhibitor (KTI) in soybean seeds. A total of 200 F3:5 lines derived from PI 547656 (low KTI) X Glenn (normal KTI) were genotyped using the BARCSoySNP6K_v2 Beadchip. F3:4 and F3:5 lines were grown in Blacksburg and Orange, Virginia in three years, respectively, and were measured for KTI content using a quantitative HPLC method. We identified three SNP markers tightly linked to the major QTL associated to low KTI in the mapping population. Based on these SNPs, we developed and validated the KASP assays in a set of 93 diverse germplasm accessions. The marker Gm08_44814503 has 86% selection efficiency for the accessions with low KTI and could be used in marker assisted breeding to facilitate the incorporation of low KTI content in soybean seeds.

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