A black soybean cultivar ‘Gyeongheukcheong’ was developed by Gyeongsangbuk-do Agricultural Research and Extension Services. ‘Gyeongheukcheong’ was selected from a cross between ‘RCS640’ and ‘Geomjeongsaeol’ in 2011. The cultivar was evaluated in multiple performance and yield trials in seven locations from 2017 to 2019. ‘Gyeongheukcheong’ has a gray pubescence, light brown pod, and dark green cotyledon, whereas ‘Cheongja 3’ has a brown pubescence, brown pod, and light green cotyledon. The seed weight and maturity of ‘Gyeongheukcheong’ was similar to that of ‘Chungja 3’. ‘Gyeongheukcheong’ was resistant to soybean mosaic virus (strain G6H), moderately resistant to bacterial pustule (caused by Xanthomonas axonopodis pv. glycines), and resistant to root rot. Total chlorophyll content (sum of chlorophyll a and b) in the green cotyledon of ‘Gyeongheukcheong’ was 48.0 μg/g, which was higher than that of ‘Cheongja 3’ (30.1 μg/g). The regional yield trial showed that ‘Gyeongheukcheong’ had a similar or significantly higher average yield than ‘Chungja 3’ in locations with single (similar) and double (19% higher) cropping systems, respectively. ‘Gyeongheukcheong’ represents a consumer-friendly black soybean with dark green cotyledons and high yield potential (Registration No. 9065).

A black soybean cultivar, “Saebaram” with green cotyledons, was developed and released by the Gyeongsangbuk-do Agricultural Research and Extension Services (GBARS) in 2019. It was developed from a single cross between “Seonheuk” and “RCS640” in 2011. The preliminary yield trial and advanced yield trial were conducted at GBARS from 2015 to 2016. The regional yield trial (RYT) was conducted in seven locations from 2017 to 2019 in Korea. “Saebaram” had purple flowers, grey pubescence, light brown pods, a black seed coat, an ellipse seed shape, and a large seed size (42.8 g/100 seeds). The seed size was significantly larger than that of the check cultivar “Cheongja 3” (36.2 g/100 seeds). Moreover, it was moderately resistant to bacterial pustule (caused by Xanthomonas axonopodis pv. glycines) and soybean mosaic virus (strain G6H). “Saebaram” had dark green cotyledons, whereas “Cheongja 3” had light green cotyledons. The total chlorophyll contents (chlorophyll a and chlorophyll b) in the green cotyledons of “Saebaram” and “Cheongja 3” were 76.1 μg/g and 30.1 μg/g, respectively. Furthermore, the RYT showed that “Saebaram” had 287 kg/10a, which was 10% higher than that of “Cheongja 3” (261 kg/10a). This black soybean cultivar with improved yield, large-size seeds, and dark green cotyledons is expected to have a high commercial value for Korean farmers (Registration No. 9155).

Understanding plant morphological and seed characteristics is an essential step for the utilization of genetic resources to improve targeted traits in soybean breeding programs. The purpose of this study was to evaluate the agronomic traits and seed pigments of 469 black soybean germplasms with green cotyledons to identify useful resources using multivariate analyses, correlation, principal component analysis (PCA), and cluster analyses. The results showed that the range of flowering days from planting were 37.7-71.5 days, harvesting days from planting were 112.3-153.0 days, plant height was 49.6-151.6 cm, and 100-seed weight was 9.1-49.3 g. According to the correlation analyses with agronomic traits, flowering and harvesting days were positively correlated with the plant height, number of nodes, and number of branches. Additionally, it was found that the chlorophyll a and total chlorophyll content had the greatest effect on the green color of the cotyledon. Based on the PCA, 13 quantitative traits were compressed into three components. The first three principal components accounted for 82.5% of the total variance. In this study, black soybean germplasms with green cotyledons were divided into four clusters by the K-means cluster analysis (non-hierarchical procedure), based on the PCA. The cluster analysis showed that chlorophyll a and plant height had a significant effect on the clustering of the black soybean germplasms used in this study. This study provides opportunities to easily select useful genetic resources for the development of new black soybean cultivars.

Cheongja4’ is a black soybean cultivar developed via a cross between ‘Milyang148’ and ‘Daemang’ in 2005. F₁ and F₂ populations were grown for 2 years, and promising lines were selected using the pedigree method from F₃ to F₅. The preliminary yield trial (PYT) and advanced yield trials (AYT) were conducted from 2011 to 2012, and regional yield trial (RYT) in 7 regions was conducted from 2013 to 2015. ‘Cheongja4’ is determinate and has purple flowers, a green cotyledon, and black spherical seeds. Flowering date and maturing date were Aug. 5 and Oct. 19, respectively. With respect to its quantitative characteristics, ‘Cheongja4’ has more pods (50) and smaller seed size (30.1g/100-seed weight) than ‘Cheongja3’ (38 and 35.2g/100-seed weight). ‘Cheongja4’ was revealed to be more tolerant to pod shattering than ‘Cheongja3’ in RYT field and indoor test. ‘Cheongja4’ had high levels of resistance to bacterial pustule and soybean mosaic virus in field and inoculation test. Although its seed quality-related characteristics were similar to those of ‘Cheongja3’, it contained more anthocyanin in the seed coat; this is the main functional component of black soybean. The mean yield of ‘Cheongja4’ in RYT was 314kg/10a, 123% of the yield of ‘Cheongja3’. ‘Cheongja4’ is expected to be widely used for variable functional purposes, such as cooking with rice and the production of processed food.

A new colored soybean variety ‘Jungmo3005’ was developed as a breeding parent. ‘Cheongjakong’ and ‘Geomjeongkong3’ were crossed in 2000. F1 and F2 populations were grown for 2 years and selected by pedigree method from F3 to F5. The preliminary yield trial (PYT) and advanced yield trial (AYT) were conducted from 2006 to 2007, and regional yield trial (RYT) in 9 regions was conducted from 2008 to 2010. ‘Jungmo3005’ is determinate, white flower, green cotyledon, green spherical seed and yellow hilum. Flowering date and maturing date were July 30 and Oct. 7, respectively. Other quantitative characteristics of ‘Jungmo3005’ were similar to ‘Cheongdu1’, but it was more tolerant to lodging and shattering than ‘Cheongdu1’ at RYT field and indoor test. Although ‘Jungmo3005’ showed symptom of mosaic disease in inoculation test at greenhouse, it had high level of resistance to soybean mosaic virus and bacterial pustule diseases at field. The yield of tofu of ‘Jungmo3005’ was more than that of ‘Cheongdu1’. The mean yield of ‘Jungmo3005’ in RYT was 256kg/10a which was 97% of the yield of ‘Cheongdu1’. ‘Jungmo3005’ is expected to be widely used as a breeding parent to cross with other varieties and lines for creating colored soybean cultivars with tolerance to lodging, shattering and bacterial pustule.