Tofu, a widely consumed soy-based product, has seen increasing consumer demand, driven by health and dietary trends. Enhancing the processing suitability of soybeans requires analysis of the genetics associated with tofu quality traits. In this study, five key traits, namely water absorption (WA%), Brix of soymilk (°BS), soymilk yield (YM%), tofu residue (TR%), and tofu yield (YT%), were evaluated in two recombinant inbred line (RIL) populations: 81 lines of “Daepung”דSaedanbaek” and 122 lines of “Daepung”דGalchae”. Most traits exhibited normal distributions and transgressive segregation. Trait correlations revealed strong associations between WA and TR, and between YM and YT, with population-specific variation. Quantitative trait locus (QTL) mapping identified eight loci in each population linked to WA, °BS, YM, TR, and YT across multiple chromosomes. Notably, co-localized QTL were detected for WA% and TR% (chromosomes 1 and 6) and for WA%, YM%, °Brix, and TR% (chromosome 8), indicating pleiotropic regulation. Candidate genes included Glyma.06g173500, associated with β-glucan biosynthesis, and Glyma.03g132700, encoding β-glucanase, both implicated in seed coat permeability and tofu yield. These results provide novel genetic insights into seed coat properties and processing quality, and the identified QTLs and candidate genes represent valuable targets for marker-assisted selection in soybean breeding programs optimized for tofu production in Korea.

Tofu is produced by mixing condensed soymilk with a coagulant. It has a low calorie and high protein and contains various important vitamins and minerals; therefore, consumption of tofu as a healthy and dietetic food has increased worldwide. For systematic application in breeding programs to increase tofu yield, evaluation of tofu characteristics is essential. To test the various characteristics of tofu, typically, a considerable amount of seeds (approximately 100 g, is required. Here, we propose a simple tofu quality test method requiring a small amount of seeds (15 g), which is 75% less than the amount needed for conventional testing. Tofu was manufactured using 20 soybean varieties with a conventional method (i.e., a tofu making machine, TM) and four simple methods: natural filtering (NF), weight pressure (WP), hand pressure (HP), and rotation machine (RM). The correlation between the five methods was assessed with respect to each tofu characteristic, and the HP and RM methods were statistically similar to the conventional methods, whereas the other methods showed differences. Regarding tofu yield, the HP and RM methods showed significantly higher correlation coefficients of 0.79 and 0.78, respectively, and the coefficient of variation between replications was also low. Therefore, the HP and RM methods were the best to easily characterize the tofu yield using a small amount of seeds. Considering the efficiency of the test, the RM method appears to be more effective than the HP method for testing multiple lines. These results will be used for the identification of quantitative trait locus/genes related to tofu quality and marker-assisted selection of breeding new soybean varieties.

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).

A yellow soybean cultivar called ‘Hipro’ was developed using the single seed descent (SSD) method by crossing ‘Saedanbaek’ (SS92414 ×MD87L) and ‘Daepung’ (Baekwon × Sinpaldal2). A preliminary yield trial (PYT), advanced yield trial (AYT), and regional yield trial (RYT) were conducted in three regions. ‘Hipro’ has a determinate growth habit, white flowers, and a spherical seed shape. In the regional yield trial, the flowering and maturity dates of ‘Hipro’ were August 4 and October 17, respectively, and the 100-seed weight was 22.2 g, which was lower than that of Daewon (26 g). Additionally, ‘Hipro’ showed resistance to lodging, soybean mosaic virus (SMV), bacterial blight, and pod shattering. The seed protein content of ‘Hipro’, which was of particular interest in this study, was 53.9%, which was higher than that of ‘Daepung’ (41.5%), and the total amino acid content without tryptophan was 43.6%, 19% higher than that of ‘Daepung’. The mean yield of ‘Hipro’ in RYT was 2.23 ton/ha, which was 91.3% of the yield of ‘Daewon’. However, ‘Hipro’ showed an 11% higher yield than Daewon in Paju. As a result of the tofu characteristic test, 'Hipro' is suitable for making soy milk and tofu due to its high solid content (12.67 Brix) and protein content (13.68%) and high yield (325%) of tofu. Overall, ‘Hipro’ had high protein content, excellent processing quality for tofu and soy milk, and strong resistance to disease and pod shattering that will greatly contribute to the consumption of soybeans in Korea. (Registration No. 7735).

Phytophthora root rot attributable to infection by the soil-borne oomycete Phytophthora sojae causes serious damage to susceptible soybeans grown in poorly drained soil. Management of this disease depends primarily on Rps (resistance to P. sojae) resistance genes. The
objective
of this study was to map resistance to two P. sojae isolates (40412 and 2457) in a Daepung×Socheong2 recombinant inbred line population. Of these two varieties, Socheong2 is resistant to the two isolates, whereas Daepung is susceptible. Single-marker analysis of variance and linkage analyses using a high-density genetic map identified different resistance loci for each isolate. A genomic region of 36.2~37.4 Mbp on chromosome 3 was identified as being associated with resistance to isolate 40412, explaining 18% of the phenotypic variance (PV), whereas, a 2.1~2.6-Mbp region on chromosome 18 was significantly associated with resistance to isolate 2457, accounting for approximately 26% of the PV. An additional region of 53.1~53.3 Mbp on chromosome 18 was also significantly associated with resistance to isolate 2457. All three loci coincide with genomic regions where an Rps gene or partial resistance have been mapped in previous studies. The respective locus showed significance for only one or the other of the isolates, indicating an isolate-specific interaction. From this finding, it can be inferred that isolates 40412 and 2457 are characterized by different avirulence genes, and that Socheong2 has at least two Rps genes that interact with each isolate. The finding of multiple Rps loci specific to an isolate within a single soybean genotype is a unique discovery. Socheong2 will accordingly be a useful genetic source for breeding resistance to multiple P. sojae isolates.

Recent climate changes have resulted in high temperatures, a greater frequency of flooding, and outbreaks of various plant diseases and insect pests, the latter of which has been characterized by a change in pest type from crop chewing to sap-sucking insects. To date, however, there has been limited study of plant resistance to sap-sucking insects. This study was carried out to evaluate the resistance and genetic patterns of the foxglove aphid Aulacorthum solani, a sap-sucking pest of soybean. We investigated the growth and reproduction of the foxglove aphid on five different varieties of soybean showing either susceptibility or resistance to this aphid in a non-choice test. Genetic analysis was conducted using the two F₂ populations derived from Daepung (susceptible to foxglove aphid)×IT104704 (resistant to foxglove aphid) and Daepung×IT188399 (resistant to foxglove aphid) crosses, which were evaluated for their responses to foxglove aphids. Differences in the responses of resistant and susceptible varieties were confirmed by monitoring aphid growth and reproduction. Although the two resistant germplasms (IT104704 and IT188399) have a strong antibiosis effect, they showed a slight difference with respect to aphid viability. Genetic analysis of foxglove aphid resistance showed that resistance was governed by a single dominant gene in IT104704 (3:1, p=0.11). We accordingly identified two resistant resources showing antibiosis to foxglove aphid, which is reported here for the first time, and also detected differences in genetic behavior. These results could be useful not only with respect to securing materials showing resistance to the foxglove aphid but also in the breeding of new foxglove aphid-resistant soybean cultivars.