In Korea, black soybeans are traditionally consumed after cooking with rice to supplement protein and oil which are lacking in rice. Seed cooking quality including seed traits after cooking with rice, which is important for consumers, were so far not comprehensively considered during the process of breeding. In this study, we first evaluated seed quality after cooking with rice, we tested the correlation between seed cooking quality and seed water absorption ratio, and we attempted to identify the Quantitative trait locus(QTL)/gene using two recombinant inbred line (RIL) populations, i.e., Daepung × Socheong2 and Daepung × Ilpumgeomjeong. Based on phenotype and correlation analyses, the main factors affecting the hardness of soybeans cooked with rice may differ between RIL population. In the Daepung × Socheong2 RIL population, one QTL associated with seed hardness after cooking with rice was identified on chromosome 11, and Glyma.11g049600, encoding peroxidase, is proposed as a candidate gene. In the Daepung × Ilpumgeomjeong RIL population, two QTLs associated with seed hardness after cooking with rice were identified on chromosomes 7 and 19, one QTL related to seed water absorption on chromosome 3, and Glyma.19g092600 encoding pectin methylesterase inhibitor are proposed as candidate genes. This is the first study on soybean cooking quality after cooking with rice, and the locations of four related QTLs were identified. The results will be of use for future development of high-quality black soybean varieties with high consumer preference using molecular breeding methods.

A black soybean cultivar called ‘Noksim’ was developed using pedigree selection by crossing ‘Ilpumgeomjeong’ (SLSB87-3 × YS558) and ‘PI547426’. A p reliminary y ield t rial (PYT), advanced y ield t rial (AYT), and regional y ield t rial (RYT) were conducted in t hree regions. ‘Noksim’ has a determinate growth habit, purple flowers, and spherical seeds. In the regional yield trial, the flowering and maturity dates of ‘Noksim’ were August 4 and October 13, respectively, and its 100-seed weight was 26.5 g, which was lower than that of ‘Chungja 3’ (36.5 g). Additionally, ‘Noksim’ showed resistance to lodging, soybean mosaic virus (SMV), bacterial blight, and pod shattering. In terms of the seed quality, the chlorophyll content of ‘Noksim’ was 71.19%, which was higher than that of ‘Chungja 3’ (50.78%), and its total anthocy anin c ontent w as 2 5.17 m g/100g, w hich w as t hree t imes more than t hat of ‘Chungja 3’. The mean y ield o f ‘Noksim’ i n RYT was 2.35 ton/ha, which was 18% greater than that of ‘Chungja 3’. ‘Noksim’ is suitable for cooking with rice and soy products such as soymilk because of its high brix degree (35 Brix) after cooking with rice, as well as its soymilk yield (71.2%). Overall, ‘Noksim’ has dark green cotyledons with a black seed coat that is preferred by consumers, and its early maturity with pod shattering resistance results in an increased seed yield. (Registration No. 7734).