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Isoflavone, protein, and oil are the most important quality traits in soybean. Since these phenotypes are typically quantitative traits, quantitative trait locus (QTL) mapping has been an efficient way to clarify their complex and unclear genetic background. However, the low-density genetic map and the absence of QTL integration limited the accurate and efficient QTL mapping in previous researches. This paper adopted a recombinant inbred lines (RIL) population derived from 'Zhongdou27'and 'Hefeng25' and a high-density linkage map based on whole-genome resequencing to map novel QTL and used meta-analysis methods to integrate the stable and consentaneous QTL. The candidate genes were obtained from gene functional annotation and expression analysis based on the public database. A total of 41 QTL with a high logarithm of odd (LOD) scores were identified through composite interval mapping (CIM), including 38 novel QTL and 2 Stable QTL. A total of 660 candidate genes were predicted according to the results of the gene annotation and public transcriptome data. A total of 212 meta-QTL containing 122 stable and consentaneous QTL were mapped based on 1,034 QTL collected from previous studies. For the first time, 70 meta-QTL associated with isoflavones were mapped in this study. Meanwhile, 69 and 73 meta-QTL, respectively, related to oil and protein were obtained as well. The results promote the understanding of the biosynthesis and regulation of isoflavones, protein, and oil at molecular levels, and facilitate the construction of molecular modular for great quality traits in soybean. [ABSTRACT FROM AUTHOR]

Significant variations of potassium absorption and utilization exist in vegetable soybean. Pot and hydroponic experiments were carried out to examine the characteristics of root potassium (K) affinity-associated drivers and photosynthesis in vegetable soybean (edamame) [ Glycine max (L.) Merr.] with different K efficiency. Two K high-efficiency vegetable soybean genotypes (Line 19 and Line 20) and two K low-efficiency genotypes (Line 7 and Line 36) were investigated in low K and normal K conditions. The root of K high-efficiency genotypes had a higher K+ affinity associated with a higher maximum K+ uptake rate (I max), but lower Michaelis constant for K+ absorption (K m) and lower compensation concentration for K+ uptake (C min). Seedlings of K high-efficiency genotypes also had higher root vigor [triphenyl tetrazolium chloride (TTC) reduction method] and greater absorbing activity (methylene blue method), especially in the low K condition. Furthermore, the root bleeding-sap rate of K high-efficiency genotypes in low K stress was 9.9–24.3% greater than that of normal K conditions, which was accompanied by a relatively higher K concentration of root bleeding-sap in contributing to K+ upward flux. The root of K high-efficiency vegetable soybean genotypes exhibited K+ high-affinity and driving advantages. Photosynthetic parameters of K high-efficiency vegetable soybean genotypes were less affected by low K stress. Low K stress decreased the net photosynthetic rate of K high-efficiency genotypes by 6.1–6.9%, while that of K low-efficiency genotypes decreased by 10.9–15.7%. The higher chlorophyll (Chl) a/b ratio with enhanced relative content of Chl a in response to low K stress might be an adapted mechanism for K high-efficiency genotypes to maintain photosynthetic capacity. Stronger root K affinity drivers associated with photosynthetic adaptability to low K stress are the key factors in determining the K high-efficiency of vegetable soybeans. [ABSTRACT FROM AUTHOR]

Field and pot experiments were conducted to select and identify the characteristics of potassium (K) high efficiency vegetable soybean genotypes. Forty genotypes under two potassium application levels (0, 120 kg ha−1 K2SO4) showed variations in K concentration, K accumulation, K internal use efficiency (KIUE) and K harvest index (KHI) in field experiment conducted in 2016. According to the distinct KIUE for yield (KIUE-Y) and KHI, two K high efficiency (KHE) genotypes (T117, L113) and two K low efficiency (KLE) genotypes (DZ1, ZX8) were used in pot experiment with two K levels (0, 120 kg ha−1 K2SO4) in 2017 for further investigation. Results indicated that KIUE-Y was significantly correlated with harvest index (HI) and KHI. Both K and dry matter (DW) were optimally distributed in the seed of KHE genotypes. In contrast, more DW and K were accumulated in vegetative organs of KLE genotypes, which was the main reason limiting K efficiency. Under K deficiency, KHE genotypes better regulate their DW and K distribution, and have higher specific leaf weight with unaffected leaf area. [ABSTRACT FROM AUTHOR]

Fruit dehiscence or seed dispersion is an essential process in the proliferation of wild plants, but it is one of the major factors leading to significant yield losses in domesticated soybean. The ventral suture is critical to pod dehiscence in soybean. To better understand the anatomy of the ventral suture in the soybean pod, we compared the dehiscence zone (DZ) and vascular bundle anatomical structure of the ventral suture using three shatter‐susceptible soybean [Glycine max (L.) Merr.] cultivars and three shatter‐resistant soybean cultivars, which had been evaluated from 140 cultivars over two growing seasons. We found that shatter‐susceptible cultivars, in the cross‐sections of ventral sutures, had a larger vascular bundle area and bundle cap area. The cells of bundle caps in shatter‐susceptible cultivars were even in shape and arranged more closely with less interstitial substance. There was a significantly shorter and straight route from the top of fiber cap cells to the connecting point of the two valves of the pod ventral suture in shatter‐susceptible cultivars than in shatter‐resistant soybean cultivars. Our findings suggest that the route from the top of fiber cap cells to the connecting point of the two valves, the vascular bundle area, the bundle cap area, and the cell arrangement in the bundle cap might be a partial mechanism involved in pod dehiscence of soybean. [ABSTRACT FROM AUTHOR]

Uptake of potassium (K) in crops depends mainly on the root system. Field, pot and hydroponic experiments were carried out to characterise root morphological traits and examine their roles in K uptake and utilisation of vegetable soybean (edamame) (Glycine max (L.) Merr.). Of 40 genotypes, two high K-efficiency (HKE) and two low K-efficiency (LKE) genotypes were identified and compared at two levels of K application: nil or 120 kg K2SO4 ha–1. HKE genotypes had shorter total root length and smaller root surface area and root volume than LKE genotypes, but responded earlier to low-K conditions by adjusting root architecture. In plants receiving nil K, total root length was increased by 10.4–21.8% for HKE genotypes but decreased by 5.5–9.5% for LKE genotypes at the V4 stage relative to plants receiving applied K. HKE genotypes were more efficient in redistributing K from source to sink tissue, especially from leaf. Of the total K in vegetative tissues, 35.0–46.4% was redistributed to seed in HKE genotypes, whereas only 19.7–28.2% was redistributed in LKE genotypes. HKE genotypes also had a higher specific K uptake rate (K uptake per unit root length), 1.6–1.7 times higher than LKE genotypes at the R5 stage. This indirectly indicated a stronger root K acquisition in HKE genotypes. This study suggests that future vegetable soybean improvement with greater K efficiency should be focused on the selection of higher K-redistribution rate and specific K-uptake rate. Breeding potassium (K)-efficient cultivars is of great importance for improving the efficiency of K-fertiliser utilisation. Genotypic variation exists for K-use efficiency in vegetable soybean, but the characteristics of high K-efficiency genotypes in vegetable soybean are still unclear. We found that high K-efficiency vegetable soybeans have higher K-redistribution capacity and strong specific root uptake rate, which could be used in breeding programs. [ABSTRACT FROM AUTHOR]

Although the effect of elevated CO2 (eCO2) on soybean yield has been well documented, few studies have addressed seed quality, particularly at the fresh edible (R6) and mature stages (R8). Under the current global scenario of increasing CO2 levels, this potentially threatens the nutritional content and quality of food crops. Using four soybean cultivars, we assessed the effects of eCO2 on the concentrations of crude protein, crude oil, and isoflavones and analyzed the changes in free amino acids, fatty acids, and mineral elements in seeds. At R6, eCO2 had no influence on soybean seed protein and oil concentrations. At R8, eCO2 significantly decreased seed protein concentration but increased seed oil concentration; it also significantly decreased total free amino acid concentration. However, at the same stage, the proportion of oleic acid (18:1) among fatty acids increased in response to eCO2 in the cultivars of Zhongke-maodou 2 (ZK-2) and Zhongke-maodou 3 (ZK-3), and a similar trend was found for linoleic acid (18:2) in Zhongke-maodou 1 (ZK-1) and Hei-maodou (HD). Total isoflavone concentrations increased significantly at both the R6 and R8 stages in response to eCO2. Compared with ambient CO2, the concentrations of K, Ca, Mg, P, and S increased significantly under eCO2 at R6, while the Fe concentration decreased significantly. The response of Zn and Mn concentrations to eCO2 varied among cultivars. At R8 and under eCO2, Mg, S, and Ca concentrations increased significantly, while Zn and Fe concentrations decreased significantly. These findings suggest that eCO2 is likely to benefit from the accumulation of seed fat and isoflavone but not from that of protein. In this study, the response of seed mineral nutrients to eCO2 varied between cultivars. [ABSTRACT FROM AUTHOR]

In order to understand the physiological mechanism of potassium (K) application in enhancing sugar content of vegetable soybean seeds, pot experiments were conducted in 2014 and 2015 with two vegetable soybean ( Glycine max L. Merr.) cultivars (c.v. Zhongkemaodou 1 and c.v. 121) under normal rate of nitrogen and phosphorus application. Three potassium (K) fertilization treatments were imposed: No K application (K0), 120 kg KSO ha at seeding (K1), and 120 kg KSO ha at seedling + 1% KSO foliar application at flowering (K2). Contents of indole-3-acetic acid (IAA), gibberellins (GA), cytokinins (ZR) and abscisic acid (ABA) in seeds were determined from 4 to 8 weeks after flowering. K fertilization increased the contents of IAA, GA, ZR, soluble sugar, sucrose and fresh pod yield, but reduced ABA content consistently. When the contents of soluble sugar and sucrose reached the highest level at 7 weeks after flowering for the 2 cultivars, the contents of IAA、GA、ZR all reached the lowest level in general. The content of ABA in seed was negatively correlated with the sucrose content ( P < 0.01, r = −0.749**, −0.768** in 2014 and −0.535**, −0.791** in 2015 for c.v.121 and c.v. Zhongkemaodou 1 respectively). The changes in ratio of the ABA to (IAA + GA + ZR) from 4 to 8 weeks after flowering affected by K application were coincident to the changes of sucrose accumulation. The reduced ratio of ABA/(IAA + GA + ZR) affected by K nutrition particularly reduced abscisic acid content plays a critical role in enhancing sucrose content, which might be a partial mechanism involved in K nutrition to improve the quality of vegetable soybean. [ABSTRACT FROM AUTHOR]

Significant differences have been reported in root K+ uptake between high potassium efficiency (HKE) and low potassium efficiency (LKE) in vegetable soybean genotypes. The ideal morphological and physiological characteristics of HKE have been defined. However, the mechanism by which HKE vegetable soybean genotypes efficiently uptake K remains unclear. By using representative materials, this study investigated the responses of root development to low K (LK) stress, and identified and assessed the key genes affecting high-efficiency K uptake between HKE and LKE vegetable soybean roots. The root growth of LKE was significantly inhibited under the LK condition. Compared with LKE, HKE had more lateral roots in both LK and CK (control) conditions. Lateral root of HKE was more preferentially responsive to exogenous IAA, with a wider response threshold to IAA concentration (from 0.1 to 1 µM). Transcriptome analysis revealed that LK induced transport-related genes up-regulated in HKE compared with LKE. In HKE, homologous genes of a K channel encoding gene potassium channel AKT1 (AKT1) and a K transporter gene high-affinity K+ transporter 5 (HAK5) were both highly expressed under the LK stress. Additionally, genes related to plant hormones signal transductions were also identified differentially expressed between the two genotypes. Plant hormone signaling involved in root morphological regulation pathways may play significant roles in improving the efficiency of vegetable soybean K+ uptake. A diagram showing possible molecular mechanisms in regulating root high-efficiency uptake K+ in vegetable soybean is proposed. [ABSTRACT FROM AUTHOR]

Abstract: Continuous soybean [Glycine max (L.) Merill.] may lead to yield decline due to its detrimental effect on soil health. Habitat disturbance affects numerous ecosystem components and processes. In this study, we assume the continuous soybean system as a normal tillage, any interference within the system is defined as a disturbance. Thus, crop disturbance is defined as a management practice used after a continuous soybean system to the seeding of the subsequent disturbed crop for one-season, and then switching to continuous soybean system. Six crops, grain soybean (Glycine max L. Merill.), wheat (Triticum aestivum L.), sugar beet (Beta vulgaris L.), tobacco (Nicotiana tabacum L.), corn (Zea mays L.), and hemp (Cannabis Satia L.) were seeded in a Mollisol farmland that had previously been cropped to continuous soybean for seven years, and then continuous soybean was implemented for three years. The soybean grain yield as a consequence of continuous soybean was significantly improved after hemp disturbance in the first and second year and after hemp and corn disturbance in the third year. The positive effect in hemp disturbance on succeeding soybean seed yield was 9.1–10.8% greater than that of continuous soybean. Increases in plant height, number of productive pod and seed number per plant as well as photosynthetic rates at R3 and R5 stage were responsible for the yield improvement of continuous soybean after hemp and corn disturbance. The attempt to increase yield of continuous soybean through the crop disturbance was considered successful. Adoption of hemp disturbance can be an alternative approach to managing continuous soybean production system. [Copyright &y& Elsevier]

Abstract: Three experiments were conducted in this study in order to investigate the impacts of soil type, soybean genotype, and the reproductive growth stage on bacterial communities in the soybean rhizosphere. Communities were evaluated by principal component analysis of denaturing gradient gel electrophoresis (DGGE) banding patterns and sequencing of partial 16S rDNA polymerase chain reaction (PCR) amplicons. A pot experiment analyzing three soybean genotypes grown in two different types of soil (Black soil and Dark Brown soil) indicated that soil type was the major factor in influencing the bacterial communities in the soybean rhizosphere, with a more significant effect observed in the Black soil samples than in the Dark Brown soil samples. A field experiment was conducted in Dark Brown soil using three soybean genotypes, and the results gleaned from both pot and field experiments indicated that bacterial communities in the soybean rhizosphere changed with growth stages, and higher number of DGGE bands observed in early reproductive growth stages, while surprisingly, a significant impact of genotype on the bacterial communities was not observed in these experiments. However, a plate culture experiment targeting the culturable bacterial communities detected a remarkable difference in the community structures of the rhizosphere between the two soybean genotypes, suggesting that a small portion of the total bacteria was influenced by genotype. Sequence analysis of DGGE bands indicated that bacterial phyla of Proteobacteria, Actinobacteria, Bacteroidetes, Nitrospirae, Firmicutes, Verrucomicrobia and Acidobacteria commonly inhabit the soybean rhizosphere. [Copyright &y& Elsevier]

Abstract: Pod and seed number are the most important yield components of soybean [Glycine max (L.) Merr.]. Leaf area index (LAI), leaf area duration (LAD) and dry matter accumulation during the reproductive period strongly influence yield components. Our objectives were: to investigate if differences in yield components exist among genotypes differing in both yield and maturity; and to examine the dynamics of dry matter accumulation, LAI, and LAD during the reproductive period for the high-yielding genotypes. Sixteen soybean genotypes within three maturity groups were grown in Hailun, China in a randomized complete block design with three replications, across 2 years. Maturity groups were selected to differ by approximately 7 days in mean days to R7 (5% of pods are mature pod color). Dry matter accumulation, LAI, and LAD were measured at R2, R4, R5, and R6 stages, respectively in each year. Yield, yield components and harvest index were determined at maturity. Late maturity genotypes had higher yield than early ones. Majority of the seed yield and components were positioned in the middle and upper part of the plant. Both pod number and seed number were higher in high-yield genotypes in each group. Seed number per pod contributed to increased yield in the high rainfall year but was not related to the variation in yield of the genotypes evaluated. Significant variations were found for LAI, LAD and dry matter within each maturity group. Higher accumulation of dry matter, higher LAI and LAD during reproductive stages were found to be closely related to high-yield genotypes in each group. No relationship was found between harvest index (HI) and seed yield. [Copyright &y& Elsevier]