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There is great interest in the enhancement of isoflavones as one of the functional ingredients in soybean. This study aimed to investigate the effects of changes in the ecological environment over different planting times on isoflavone content. A total of 28 Korean soybean cultivars were grown at different planting times in late May, mid-June, and early July and their isoflavone content was measured over 2 years (2017 and 2018). Analyses of variance revealed significant effects of genotypes, planting times, years, and their interactions on isoflavone content. The average content of total isoflavone, as well as its component groups of malonylglucoside and aglycon, increased significantly as the seed planting time was delayed from late May to early July. The accumulation of each isoflavone component varied with changes in the planting time. The isoflavone content of the soybean cultivars for soy-sprout and soy-paste and tofu were higher for plantings in early July than for those in late May and/or mid-June, except for the black soybean cultivars. Despite significant correlations of the isoflavone content of the 28 cultivars among the three planting times, the responses of individual cultivars varied in isoflavone content by planting time. When planting was delayed, the time to flowering and maturity was also delayed and the number of days of growth from planting or flowering to maturity decreased; however, this was not related to isoflavone content. When planting was delayed, the temperature during the ripening period from flowering to maturity was lower, which was inversely related to the isoflavone content.

Flooding stress causes severe yield reduction in soybean worldwide. The development of stress-tolerant cultivars could be an effective measure to reduce the negative effects of flooding stress. Molecular information on the gene expression pattern of tolerant and susceptible genotypes under flooding stress could be valuable to improve the flooding tolerance in soybean. The objective of this study was to analyze the differentially expressed genes (DEGs) revealed by RNA sequencing in the soybean leaf tissues of tolerant (‘Paldalkong’ and ‘Danbaekkong’) and susceptible (‘NTS1116’) cultivars under flooding stress. Seedlings were grown in a well-watered condition up to the V1–V2 stage and flood-stressed by inundating ~ 10-cm water for 14 days. A total of 22,468 genes were differentially expressed in flood-stressed condition compared to the well-watered control condition, out of which 13,729, 13,405, and 13,160 were differentially expressed in ‘Paldalkong’, ‘Danbaekkong’, and ‘NTS1116’, respectively. A higher number of some of the flooding tolerance-related genes such as lipoxygenase, expansin, glutathione S-transferase, and sugar efflux transporter were up-regulated in the tolerant cultivars than in the susceptible cultivar. The number of some abscisic acid-related transcription factors of basic leucine zipper domain and myeloblastosis families was also higher in the tolerant cultivars than in the susceptible cultivar. The molecular information about the DEGs of tolerant and susceptible cultivars obtained in the present study could be valuable to improve the flooding tolerance in soybeans.

Domestic rice production has exceeded the demand in Korea and cultivation of upland crops like soybean has been increased in converted paddy fields. The objective of this study was to investigate the effect of two soil types, upland and paddy, on flooding tolerance of three tolerant and three susceptible soybean cultivars under greenhouse conditions. The flooding tolerance of soybean cultivars was evaluated based on chlorophyll content (CC), plant height (PH), and shoot dry weight (DW) measured under unflooded control and flooded treatments for 14 days. These three parameters were significantly (P < 0.01) affected by the soil type during the flooding and flood recovery periods of 14 days. Mean flooding tolerance index (FTI) of susceptible cultivars was higher than that of tolerant cultivars in upland soil. However, the FTI of tolerant cultivars was greater than that of susceptible cultivars in paddy soil at 14 days after flooding (DAF). A non-significant negative correlation between CC and DW and a significant (P < 0.01) positive correlation between PH and DW were found in both soils, whereas the negative correlation between CC and PH was non-significant in upland soil and was significant (P < 0.01) in paddy soil at 14 DAF. The results suggested that the flooding tolerance level of soybean cultivars could be influenced by soil type hence, it could be useful to consider designing flooding tolerance studies in different soil types. Also, field experiments could be designed to observe data until harvest to verify that with vegetative parameters of tolerant soybean varieties.

Flooding stress is a serious problem in soybean production, causing a remarkable yield reduction. The onset of rainy season during the early growth of soybean in Korea and some other parts of the world potentially subjects soybean plants to flooding stress. The objective of this study was to map quantitative trait loci (QTL) for flooding tolerance using a recombinant inbred line (RIL) population derived from a cross between ‘Danbaekkong’ (flood-tolerant) and ‘NTS1116′ (flood-susceptible) cultivars grown in a plastic house for two years. The plants were flood-stressed at the V1-V2 stage by ponding about 10 cm water from the soil surface. Leaf chlorophyll content and shoot dry weight were measured under control and flooded conditions to map the QTL. The genetic map was constructed using 1689 polymorphic markers obtained from the 180K Axiom® SoyaSNP markers used for genotyping the population. Ten QTL with 3.39−5.14 logarithm of odds scores and 8.1−30.7% phenotypic variations (PVE) were identified on seven chromosomes. One QTL on chromosomes 6 and 15 and two QTL on chromosome 7 were detected at least in two different environments causing up to 30.7% PVE, suggesting their potential applications in the breeding of flood-tolerant soybeans. The results could be useful in further exploring the genetic basis of flooding tolerance and developing tolerant cultivars of soybean.

Significant yield losses are caused by pod shattering during the harvest of domesticated crop plants. The phenotype evaluation of pod shattering requires fully grown plants, and it is a labor-intensive and time-consuming procedure. The purpose of this study was to test the applicability of previously identified KSS-SNP5 SNP marker on chromosome 16 in the marker assisted selection (MAS) system for pod shattering in soybean breeding programs. For this research, TaqMan SNP assay was successfully developed to detect the A/G allele of the KSS-SNP5 marker in the breeding materials, including two breeding stages, F2:3 populations, and yield trial stage breeding lines. The MAS prediction accuracy was calculated by comparing the genotyping data from the TaqMan assay with the phenotype data from the dry-oven method. The total MAS prediction accuracy was 92.5% and 96.2% in two F2:3 populations and breeding lines, respectively and 85% and 96% accuracy were shown in severe conditions. In this study, we confirmed that the KSS-SNP5 TaqMan probe tightly linked to pod shattering is effective to select a resistant line. Based on these results, we propose that the marker tightly linked to pod shattering can be of valuable use in soybean breeding program for the development of pod shattering-resistant cultivars.

First pod height (FPH) is an agronomic trait for the mechanical harvesting of soybeans with combines. The seed loss could be minimized, if the FPH is higher than the height of the cutter bar in combines. Hence, developing soybeans with high FPH has become one of important breeding goals in current crop improvement programs. The objective of this study was to evaluate genetic and environmental variation of FPH in soybean and to analyze the effect of ratio of FPH to plant height (PH) on seed yield. Four genotypes were evaluated across six different environments to analyze environmental variation of agronomic traits including FPH. Three F2 populations were evaluated to analyze genetic variation and relationship between the ratio of FPH to PH and seed yield. The main effects of planting distance, genotype and seeding date were significant for FPH, but FPH is affected more by genetic factors than by environmental factors. The mean heritability value of FPH was 66% across three F2 populations. Seed yield was found to reduce with increase in the FPH/PH ratio. In conclusion, genetic factors have effect more than environments to the variation of FPH. While FPH is higher than cutting height, the smaller ratio can minimize seed yield decrease.

Drought stress, which is increasing with climate change, is a serious threat to agricultural sustainability worldwide. Seed germination is an essential growth phase that ensures the successful establishment and productivity of soybean, which can lose substantial productivity in soils with water deficits. However, only limited genetic information is available about how germinating soybean seeds may exert drought tolerance. In this study, we examined the germinating seed drought-tolerance phenotypes and genotypes of a panel of 259 released Chinese soybean cultivars panel. Based on 4616 Single-Nucleotide Polymorphisms (SNPs), we conducted a mixed-linear model GWAS that identified a total of 15 SNPs associated with at least one drought-tolerance index. Notably, three of these SNPs were commonly associated with two drought-tolerance indices. Two of these SNPs are positioned upstream of genes, and 11 of them are located in or near regions where QTLs have been previously mapped by linkage analysis, five of which are drought-related. The SNPs detected in this study can both drive hypothesis-driven research to deepen our understanding of genetic basis of soybean drought tolerance at the germination stage and provide useful genetic resources that can facilitate the selection of drought stress traits via genomic-assisted selection.