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.