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).

Low-temperature damage at the seedling stage is one of the most significant natural obstacles to wheat’s growth. In domestic wheat breeding programs, the selection of cold-tolerant varieties is crucial for the development of superior wheat varieties. Traditionally, the extent of damage caused by freezing wheat is estimated through visual observation. In this study, we compared the RGB image analysis method with conventional visual evaluation and chlorophyll content analysis methods to determine if this method could accurately quantify the cold tolerance discrimination of wheat in the field. First, single-leaf-level RGB image analysis revealed a pattern similar to dead leaf ratio and chlorophyll content in three grades of freezing injury. Next, we compared the significance of plant-level RGB image analysis. The greenness index by RGB image analysis showed a higher correlation with dead leaf ratio by visual evaluation. Finally, 40 wheat varieties were planted in the field and wheat canopy images were collected at the seedling stage after wintering. There was a high correlation between the greenness index and the visual evaluation. However, there was no correlation between dead leaf ratio and visual evaluation or greenness index as determined by RGB image analysis. These findings suggest that using RGB image analysis rather than visual evaluation can be useful in assessing freeze damage in wheat fields.

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.

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).

Chlorophyll is an essential pigment involved in light absorption and electron transfer in photosynthesis, a photochemical process that is indispensable for plant growth and development. The biosynthesis of chlorophyll occurs in plastids and shares a common biosynthetic pathway with other tetrapyrroles. The chlorophyll metabolic pathway is divided into four distinct components: the common pathway, chlorophyll-specific biosynthetic pathway, chlorophyll cycle, and chlorophyll degradation pathway, which are regulated in developmental- and environmental-specific manners. During the early stages of plant growth, the expression of most chlorophyll biosynthetic genes is induced by light, resulting in an increase in chlorophyll accumulation, induction of high photosynthetic activity, and continuous plant growth. In contrast, during plant maturation, the expression of most of these genes is gradually downregulated, whereas genes involved in chlorophyll degradation are upregulated during leaf senescence. Chlorophyll biosynthesis is directly or indirectly regulated by the members of various transcription factor families. In this review, we describe representative mechanisms of transcription factor-mediated activation and repression of chlorophyll biosynthesis in response to light treatment. We also present an overview of recent studies that have examined all the enzymatic steps involved in chlorophyll metabolic pathways and their gene regulation at the transcriptional level, which will enable readers to gain a better understanding of chlorophyll metabolism.