Development Of Soybean Cultivars Research Articles

Comparative Morpho-Physiological, Biochemical, and Gene Expressional Analyses Uncover Mechanisms of Waterlogging Tolerance in Two Soybean Introgression Lines.

Waterlogging is one of the key abiotic factors that severely impedes the growth and productivity of soybeans on a global scale. To develop soybean cultivars that are tolerant to waterlogging, it is a prerequisite to unravel the mechanisms governing soybean responses to waterlogging. Hence, we explored the morphological, physiological, biochemical, and transcriptional changes in two contrasting soybean introgression lines, A192 (waterlogging tolerant, WT) and A186 (waterlogging sensitive, WS), under waterlogging. In comparison to the WT line, waterlogging drastically decreased the root length (RL), shoot length (ShL), root fresh weight (RFW), shoot fresh weight (ShFW), root dry weight (RDW), and shoot dry weight (ShDW) of the WS line. Similarly, waterlogging inhibited soybean plant growth by suppressing the plant's photosynthetic capacity, enhancing oxidative damage from reactive oxygen species, and decreasing the chlorophyll content in the WS line but not in the WT line. To counteract the oxidative damage and lipid peroxidation, the WT line exhibited increased activity of antioxidant enzymes such as peroxidase (POD), superoxide dismutase (SOD), and catalase (CAT), as well as higher levels of proline content than the WS line. In addition, the expression of antioxidant enzyme genes (POD1, POD2, FeSOD, Cu/ZnSOD, CAT1, and CAT2) and ethylene-related genes (such as ACO1, ACO2, ACS1, and ACS2) were found to be up-regulated in WT line under waterlogging stress conditions. In contrast, these genes showed a down-regulation in their expression levels in the stressed WS line. The integration of morpho-physiological, biochemical, and gene expression analyses provide a comprehensive understanding of the responses of WT and WS lines to waterlogging conditions. These findings would be beneficial for the future development of soybean cultivars that can withstand waterlogging.

Morph-physiology and development of soybean cultivars under irrigation shift

During certain periods of the year, some Brazilian regions impose water restrictions, initiating the growth cycle of the soybean crop. Thus, this work was conducted aiming to evaluate the morphophysiology and development of soybean cultivars under irrigation intervals. The experiment was conduct in January 2021, in a rural property, located in the municipality of Lavínia, state of São Paulo, Brazil. The design was completely randomized, in a 2×5 factorial scheme, with two soybean cultivars, M7110IPro (Monsoy®) and Desafio RR8473RSF (Brasmax®), interacting with the irrigation intervals (i.e., 24 h (Control); 48 h; 72 h, 96 h and 120 h) totalizing 10 treatments. We used four repetitions per treatment, which totalizes 40 plots or pots. Our results revealed that intervals longer than 48 h already negatively influence in morphophysiology of the soybean crop. Intervals of 96 h caused greater negative interferences on plant height (PH); number of leaflets (NL); number of pods (NP); dry mass of aerial part (DMAP) and root (DMR) in the soybean crop when grown in pots. Water stress did not influence the stomatal density of soybean grown in pots. Water stress harms soybean physiological parameters. No soybean cultivar showed tolerance to water stress.

Overexpression of soybean GmNAC19 and GmGRAB1 enhances root growth and water-deficit stress tolerance in soybean.

Soybean (Glycine max) is an important crop in agricultural production where water shortage limits yields in soybean. Root system plays important roles in water-limited environments, but the underlying mechanisms are largely unknown. In our previous study, we produced a RNA-seq dataset generated from roots of soybean at three different growth stages (20-, 30-, and 44-day-old plants). In the present study, we performed a transcriptome analysis of the RNA-seq data to select candidate genes with probable association with root growth and development. Candidate genes were functionally examined in soybean by overexpression of individual genes using intact soybean composite plants with transgenic hairy roots. Root growth and biomass in the transgenic composite plants were significantly increased by overexpression of the GmNAC19 and GmGRAB1 transcriptional factors, showing up to 1.8-fold increase in root length and/or 1.7-fold increase in root fresh/dry weight. Furthermore, greenhouse-grown transgenic composite plants had significantly higher seed yield by about 2-fold than control plants. Expression profiling in different developmental stages and tissues showed that GmNAC19 and GmGRAB1 were most highly expressed in roots, displaying a distinct root-preferential expression. Moreover, we found that under water-deficit conditions, overexpression of GmNAC19 enhanced water stress tolerance in transgenic composite plants. Taken together, these results provide further insights into the agricultural potential of these genes for development of soybean cultivars with improved root growth and enhanced tolerance to water-deficit conditions.

Genome-wide survey identified superior and rare haplotypes for plant height in the north-eastern soybean germplasm of China

The proper and efficient utilization of natural genetic diversity can significantly impact crop improvements. Plant height is a quantitative trait governing the plant type as well as the yield and quality of soybean. Here, we used a combined approach including a genome-wide association study (GWAS) and haplotype and candidate gene analyses to explore the genetic basis of plant height in diverse natural soybean populations. For the GWAS analysis, we used the whole-genome resequencing data of 196 diverse soybean cultivars collected from different accumulated temperature zones of north-eastern China to detect the significant single-nucleotide polymorphisms (SNPs) associated with plant height across three environments (E1, E2, and E3). A total of 33 SNPs distributed on four chromosomes, viz., Chr.02, Chr.04, Chr.06, and Chr.19, were identified to be significantly associated with plant height across the three environments. Among them, 23 were consistently detected in two or more environments and the remaining 10 were identified in only one environment. Interestingly, all the significant SNPs detected on the respective chromosomes fell within the physical interval of linkage disequilibrium (LD) decay (± 38.9 kb). Hence, these genomic regions were considered to be four quantitative trait loci (QTLs), viz., qPH2, qPH4, qPH6, and qPH19, regulating plant height. Moreover, the genomic region flanking all significant SNPs on four chromosomes exhibited strong LD. These significant SNPs thus formed four haplotype blocks, viz., Hap-2, Hap-4, Hap-6, and Hap-19. The number of haplotype alleles underlying each block varied from four to six, and these alleles regulate the different phenotypes of plant height ranging from dwarf to extra-tall heights. Nine candidate genes were identified within the four haplotype blocks, and these genes were considered putative candidates regulating soybean plant height. Hence, these stable QTLs, superior haplotypes, and candidate genes (after proper validation) can be deployed for the development of soybean cultivars with desirable plant heights.

SoyMAGIC: An Unprecedented Platform for Genetic Studies and Breeding Activities in Soybean.

Multi-Parent Advanced Generation Inter-Cross (MAGIC) populations are emerging genetic platforms for high-resolution and fine mapping of quantitative traits, such as agronomic and seed composition traits in soybean (Glycine max L.). We have established an eight-parent MAGIC population, comprising 721 recombinant inbred lines (RILs), through conical inter-mating of eight soybean lines. The parental lines were genetically diverse elite cultivars carrying different agronomic and seed composition characteristics, including amino acids and fatty acids, as well as oil and protein concentrations. This study aimed to introduce soybean MAGIC (SoyMAGIC) population as an unprecedented platform for genotypic and phenotypic investigation of agronomic and seed quality traits in soybean. The RILs were evaluated for important seed composition traits using replicated field trials during 2020 and 2021. To measure the seed composition traits, near-infrared reflectance (NIR) was employed. The RILs were genotyped using genotyping-by-sequencing (GBS) method to decipher the genome and discover single-nucleotide polymorphic (SNP) markers among the RILs. A high-density linkage map was constructed through inclusive composite interval mapping (ICIM). The linkage map was 3,770.75 cM in length and contained 12,007 SNP markers. Chromosomes 11 and 18 were recorded as the shortest and longest linkage groups with 71.01 and 341.15 cM in length, respectively. Observed transgressive segregation of the selected traits and higher recombination frequency across the genome confirmed the capability of MAGIC population in reshuffling the diversity in the soybean genome among the RILs. The assessment of haplotype blocks indicated an uneven distribution of the parents’ genomes in RILs, suggesting cryptic influence against or in favor of certain parental genomes. The SoyMAGIC population is a recombined genetic material that will accelerate further genomic studies and the development of soybean cultivars with improved seed quality traits through the development and implementation of reliable molecular-based toolkits.

Desenvolvimento de cultivares de soja de crescimento indeterminado após a poda apical

Algumas cultivares de soja de ciclo perene podem apresentar plasticidade na brotação dos ramos laterais, ou mesmo, pode ser estimulado após a sua poda apical em diferentes estádios fenológicos da cultura. Diante do exposto esse trabalho teve por objetivo avaliar o desenvolvimento de cultivares de soja de crescimento indeterminado após a poda apical. O experimento foi realizado em outubro de 2019, nas Faculdades Integradas Stella Maris (FISMA), localizada no Município de Andradina, Estado de São Paulo. O delineamento foi inteiramente casualizado, em esquema fatorial de 2x4, sendo dois cultivares de soja, DM81I84 IPRO e SYN 1687 IPRO, interagindo com a poda apical em quatro estádios diferentes de desenvolvimento, sendo eles: ausência de poda (controle),  V4, V8 e R2, perfazendo oito tratamentos e com cinco repetições, totalizando 40 parcelas ou vasos. Não é recomendada a poda apical nas cultivares de soja DM81I84 IPRO e SYN 1687 IPRO. A poda apical na fase reprodutiva da soja influencia de maneira negativa a produtividade da cultura. A cultivar de soja DM81I84 IPRO se destacou nas características de produção. O número de galhos apresenta uma correlação positiva com a produtividade na cultura da soja.

Association mapping to identify molecular markers associated with resistance genes to stink bugs in soybean

Damage generated by insects is one of main restricting factors for soybean production. Stink bugs are a great threat within pests because, by feeding mainly on pods, they cause direct and irreversible damage to developing seeds. Thus, plant resistance is an important management strategy to reduce insect population impact on yield losses. Association mapping can be used as a powerful tool for dissecting resistance mechanisms in soybean, more specifically to recover functional loci involved in plant defense against herbivorous insects; and can also provide valuable markers for the development of soybean cultivars with resistance. The purpose of this study was to identify molecular markers associated with resistance genes to stink bugs in a collection of soybean germplasm, using the association mapping strategy. According to the decline value in the linkage disequilibrium, an accurate power of mapping resolution was predicted in this population. Four associated markers located in chromosomes 6 and 15 were identified. Out of the 112 candidate genes close to them, 31 would encode proteins related to defense pathways triggered by the attack of herbivorous insects. The proteins encoded by these candidate genes could be associated to the jasmonic acid pathway. The main contribution of this study was the identification of molecular markers associated with resistance genes to stink bugs. These markers will be a useful tool for marker-assisted selection applied to soybean genetic breeding.

Genome-wide genetic diversity is maintained through decades of soybean breeding in Canada.

Genetic diversity in Canadian soybean is maintained over decades of selection in two public breeding programs. Breeders have used a portion of the genetic diversity available in germplasm collections. Both public and private breeding efforts have been critical for the development of soybean cultivars grown around the world. Global genetic diversity of soybean has been well characterized; however, this diversity is not well studied at the breeding program scale. The objective of this study was to characterize genetic diversity over decades of breeding in two public soybean breeding programs at the University of Guelph, Canada. To address this objective, a pedigree-related panel combining 296 soybean accessions from the Ridgetown and Guelph Campus breeding programs was studied. The accessions were genotyped using genotyping-by-sequencing, imputed using the GmHapMap reference genotypes resulting in more than 3.8M SNPs, further filtered to 77k SNPs. Population structure analysis did not identify structure between the breeding programs and historical germplasm. The linkage disequilibrium decay ranged from 400 to 600kb on average in euchromatic regions. Nucleotide diversity over decades of breeding shows that historical accessions had the highest nucleotide diversity, with significant decreases corresponding to the initial breeding activity in Canada; however, genetic diversity has increased in the last 20years in both breeding programs. Maturity gene E2 was nearly fixed for e2 in Ridgetown accessions, while unfixed in Guelph accessions. Comparison of the breeding programs to the USDA germplasm collection reveals that breeders have only used a portion of the available genetic diversity, allowing future breeders to exploit this untapped resource. The approach used in this study may be of interest to other breeding programs for evaluating changes in genetic diversity resulting from breeding activities.

Environmental Stability Study of Soybeans with Modified Carbohydrate Profiles in Maturity Groups 0 to V

ABSTRACTSoybean [Glycine max (L.) Merr.] is an important crop in the United States that is processed into two main products: a vegetable oil and a high‐protein meal used in livestock rations. Soybean cultivar development involves the incorporation of new traits that enhance value for the producer, processor, or end user. Soybean varieties that have seed composition characteristics that improve the value of the meal while still allowing high yields are desirable. The raffinose family of oligosaccharides (RFO) are antinutritional carbohydrates that reduce the nutritional energy of soybean meal, whereas sucrose can be considered nutritionally beneficial in soybean meal. The objective of this study was to expand the understanding of the environmental stability of the carbohydrate profiles for soybean lines containing different allele combinations of two key raffinose synthase (RS2 and RS3) genes, as well as targeted maturity gene combinations in a range of US soybean production environments. The results indicated that soybean genotypes with combinations of variant alleles of the RS2 and RS3 genes, as well as maturity genes appropriate for their targeted environment, produced characteristic carbohydrate profiles. Environmental factors did have an effect on carbohydrate components, particularly for sucrose. None of the genotype classes was stable for sucrose, although most of the variant RS2 genotypes accumulated at least 7% sucrose over the studied environments. In addition, five of the six genotype classes were stable for stachyose. The results establish the genotype classes with rs2W331− alleles suitable to develop soybean cultivars in broad maturity group backgrounds that have an enhanced energy meal trait.

Introgression of novel genetic diversity to improve soybean yield.

Exotic soybean germplasm can be used to increase novel genetic diversity and yield potential of cultivars. Modern North American soybean (Glycine max [L.] Merr.) cultivars have been derived from only a few ancestors. The objectives of this research were to develop breeding lines with novel genetic diversity that were equivalent to the yield of a commercial cultivar parent and within those lines identify regions of novel genetic diversity that were not present in the Corteva Agriscience elite soybean germplasm pool. Nine lines created from diverse germplasm (USDA-ARS breeding program at the University of Illinois) were crossed to a RM34Elite parent to develop populations and sublines for yield testing. Across yield tests at 30 locations conducted between 2014 and 2016, eleven breeding lines were identified that were equivalent to or significantly higher in yield when compared to the RM34Elite parent. Among the eleven final lines, the introgressed novel haplotypes that were not present in current Corteva Agriscience soybean germplasm occupied an estimated 0.8-10.0% of the genome. JH-2665, the highest yielding line across 3years of testing, yielded 280kg/ha more than the RM34Elite parent and had an estimated 8.6% of the genome containing novel diversity haplotypes. JH-2665 had 96 regions of novel diversity introgression ranging from 1 to 12cM in size, with six regions over 6cM in length. The methods reported demonstrate how high-yielding lines with novel genetic diversity can be developed. This material will be useful for expanding the genetic diversity needed to improve genetic gain in future soybean cultivar development.

Comprehensive RNA sequencing and co-expression network analysis to complete the biosynthetic pathway of coumestrol, a phytoestrogen

Coumestrol (CMS), a coumestan isoflavone, plays key roles in nodulation through communication with rhizobia, and has been used as phytoestrogens for hormone replacement therapy in humans. Because CMS content is controlled by multiple genetic factors, the genetic basis of CMS biosynthesis has remained unclear. We identified soybean genotypes with consistently high (Daewonkong) or low (SS0903-2B-21-1-2) CMS content over 2 years. We performed RNA sequencing of leaf samples from both genotypes at developmental stage R7, when CMS levels are highest. Within the phenylpropanoid biosynthetic pathway, 41 genes were tightly connected in a functional co-expression gene network; seven of these genes were differentially expressed between two genotypes. We identified 14 candidate genes involved in CMS biosynthesis. Among them, seven were annotated as encoding oxidoreductases that may catalyze the transfer of electrons from daidzein, a precursor of CMS. Two of the other genes, annotated as encoding a MYB domain protein and a MLP–like protein, may increase CMS accumulation in response to stress conditions. Our results will help to complete our understanding of the CMS biosynthetic pathway, and should facilitate development of soybean cultivars with high CMS content that could be used to promote the fitness of plants and human beings.

Improvement of soybean cultivars for natto production through the selection of seed morphological and physiological characteristics and seed compositions: A review

AbstractNatto, a traditional soyfood fermented by Bacillus subtilis (natto), is prepared by steaming/cooking of soaked soybean seeds followed by inoculation with the bacteria and incubation. Natto soybean has increased in popularity due to its nutritional value and health benefits. Thus, the natto soybean market provides additional opportunities for farmers. The development of soybean cultivars with improved natto quality characteristics is crucial for maintaining and increasing the natto soybean market. Good‐quality characteristics of natto are determined by soybean cultivar, processing conditions and bacteria strain. Natto quality evaluation generally determined by sensory panels is time consuming. Therefore, indirect selection for natto quality based on seed traits is preferred. Seed morphological and physiological characteristics and seed compositions play an important role in producing natto of good quality. In this review, we have summarized natto processing conditions, natto quality characteristics, seed traits involved in natto quality and their genetic variation, as well as the genetic diversity in food‐grade soybean germplasms and B. subtilis strains. Information presented will be helpful for natto soybean cultivar development and natto manufacture.

Development And Grain Quality Of Soybean Cultivars Treated With Pyraclostrobin And Biostimulant

Products with physiological effects on plants to optimize agricultural production is increasingly used; they can change the development of plants and the chemical characteristics of seeds. The objective of this work was to evaluate the development of soybean cultivars and the protein and oil contents of soybean grains after treatment with pyraclostrobin and biostimulant. The experiment was carried out with soybean crops without irrigation. The experimental design was a randomized complete block design, with five replications, using a 3 × 3 factorial arrangement consisting of three cultivars of different maturation times (very early, M6952IPRO; early M7739IPRO; and medium, ST797IPRO), and three treatments with products that cause physiological effects (control, pyraclostrobin, and control + biostimulant). The pod, leaf, and stem dry weights, number of pods, 100-grain weight, grain yield, and oil and protein contents of the soybean plants were evaluated. The data were subjected to analysis of variance, and Tukey’s test at 5% probability. The effects of the products used (pyraclostrobin and biostimulant) vary according to the cultivar and may increase the soybean leaf and pod dry weights, and grain protein contents.

Environmental Stability of Carbohydrate Profiles in Different Soybean Genotypes

Soybean [Glycine max (L.) Merr.] is an important annual crop. The raffinose family oligosaccharides (RFOs) raffinose and stachyose are antinutritional carbohydrates present in soybean seeds. Consumption of soybean seed products with low RFO reduced flatulence in humans and increased metabolizable energy efficiency in chickens, pigs, and dogs. The development of soybean cultivars producing high metabolizable energy with low antinutritional factors in the seed is one avenue to increase soybean value. The soybean line PI 200508 with low RFO content was previously characterized to have a reduction of seed raffinose synthase enzyme activity. A variant allele of the raffinose synthase 2 gene (RS2) with a 3‐bp deletion leading to the elimination of a single conserved amino acid residue (RS2, rs2W331−) in PI 200508 was associated with the seed RFO phenotype. Another missense allele of RS2 and variant alleles of the RS3 gene have been identified. The objective of this study was to determine the environmental stability of the carbohydrate profiles for soybean lines containing different allele combinations of two key raffinose synthase (RS2 and RS3) genes in two locations over 2 yr. Although this study was conducted with different genetic backgrounds, the results indicated that the carbohydrate profile in soybean seed is mostly determined by RS2 and RS3 genotype, and galactinol and sucrose content were mainly affected by environmental factors. Genotype was the major factor for the RFO content in soybean seeds, and soybean lines with the rs2W331− allele of RS2 were the most stable for sucrose and RFOs over four environments. A novel genetic combination of RS2 and RS3 alleles demonstrated the importance of multiple variant alleles contributing to seed raffinose synthase activity.

Discovery of a seventh Rpp soybean rust resistance locus in soybean accession PI 605823.

A novel Rpp gene from PI 605823 for resistance to Phakopsora pachyrhizi was mapped on chromosome 19. Soybean rust, caused by the obligate biotrophic fungal pathogen Phakopsora pachyrhizi Syd. & P. Syd, is a disease threat to soybean production in regions of the world with mild winters. Host plant resistance conditioned by resistance to P. pachyrhizi (Rpp) genes has been found in numerous soybean accessions, and at least 10 Rpp genes or alleles have been mapped to six genetic loci. Identifying additional disease-resistance genes will facilitate development of soybean cultivars with durable resistance. PI 605823, a plant introduction from Vietnam, was previously identified as resistant to US populations of P. pachyrhizi in greenhouse and field trials. In this study, bulked segregant analysis using an F2 population derived from 'Williams 82'×PI 605823 identified a genomic region associated with resistance to P. pachyrhizi isolate GA12, which had been collected in the US State of Georgia in 2012. To further map the resistance locus, linkage mapping was carried out using single-nucleotide polymorphism markers and phenotypic data from greenhouse assays with an F2:3 population derived from Williams 82×PI 605823 and an F4:5 population derived from '5601T'×PI 605823. A novel resistance gene, Rpp7, was mapped to a 154-kb interval (Gm19: 39,462,291-39,616,643 Glyma.Wm82.a2) on chromosome 19 that is different from the genomic locations of any previously reported Rpp genes. This new gene could be incorporated into elite breeding lines to help provide more durable resistance to soybean rust.

English

The continuous development of soybean cultivars aiming at higher yields can result in a demand of N supply higher than the standard inoculation with Bradyrhizobium species. In this context, Azospirillum species, a nitrogen-fixing microorganism found in the rhizosphere of various plant species, may be studied as a way of providing soybean crop with the part of the N it needs. Employing a completely randomized design with four replicates, this study aimed to evaluate the agronomic performance of two different methods of standard inoculation of Bradyrhizobium spp. associated with the co-inoculation with Azospirillum spp. The tested treatments consisted of the absence of N fertilizer and inoculant, full N recommendation, two single inoculations with Bradyrhizobium spp. (in-furrow and seed-applied) combined with an in-furrow application of Azospirillum spp. At R2 growth stage, the nodule number, nodule dry weight, shoot dry biomass and shoot N content were the variables evaluated, whereas at R8 the grain yield, thousand seed weight and grain N content were assessed. The results demonstrated that the co-inoculation of Bradyrhizobium spp. with Azospirillum brasilense is beneficial to soybean yield, mainly using the in-furrow method of application for Bradyrhizobium spp., associated to the in-furrow co-inoculation with Azospirillum spp.   Key words: Glycine max, inoculation, nitrogen content, yield.

Extending the evaluation of the SoySim model to soybean cultivars with high maturation groups

SoySim is a dynamic process-based model for soybean that requires fewer genotype-specific parameters compared to other soybean models such as the CROPGRO-Soybean model. The SoySim model was originally developed and evaluated using cultivars with maturity group (MG) ratings from 0.8 to 4.2 in temperate climate and mid latitudes. The objective of this study was to evaluate the SoySim model for simulating growth, development and yield of soybean cultivars with MG greater than 4.2 grown in the subtropics of Southern Brazil. The range of maturity groups used in this study was from 4.8 to 8.2, including indeterminate and semi-determinate soybean cultivars. Data for model evaluation were from well-managed twelve field experiments across the Rio Grande do Sul State, including on-farm experiments, during five growing seasons (2010/2011–2014/2015), with sowing dates before, during and after the recommended period, and yield ranging from 1.5 to 5.9Mgha−1. The errors in the prediction of final node number, R-stages, LAI and seed yield were high mainly for soybean cultivars with maturation group greater than 6, indicating weaknesses of the model in simulating growth and development of cultivars in environment outside the range where the model was calibrated. We conclude that there is a need to review parameters and relationships in the SoySim model to better describe the effect of environment factors, such as temperature and photoperiod, on growth and development of soybean cultivars with maturity group greater than 6, typically used in the tropics and subtropics.

Advancements in breeding, genetics, and genomics for resistance to three nematode species in soybean.

Integration of genetic analysis, molecular biology, and genomic approaches drastically enhanced our understanding of genetic control of nematode resistance and provided effective breeding strategies in soybeans. Three nematode species, including soybean cyst (SCN, Heterodera glycine), root-knot (RKN, Meloidogyne incognita), and reniform (RN, Rotylenchulus reniformis), are the most destructive pests and have spread to soybean growing areas worldwide. Host plant resistance has played an important role in their control. This review focuses on genetic, genomic studies, and breeding efforts over the past two decades to identify and improve host resistance to these three nematode species. Advancements in genetics, genomics, and bioinformatics have improved our understanding of the molecular and genetic mechanisms of nematode resistance and enabled researchers to generate large-scale genomic resources and marker-trait associations. Whole-genome resequencing, genotyping-by-sequencing, genome-wide association studies, and haplotype analyses have been employed to map and dissect genomic locations for nematode resistance. Recently, two major SCN-resistant loci, Rhg1 and Rhg4, were cloned and other novel resistance quantitative trait loci (QTL) have been discovered. Based on these discoveries, gene-specific DNA markers have been developed for both Rhg1 and Rhg4 loci, which were useful for marker-assisted selection. With RKN resistance QTL being mapped, candidate genes responsible for RKN resistance were identified, leading to the development of functional single nucleotide polymorphism markers. So far, three resistances QTL have been genetically mapped for RN resistance. With nematode species overcoming the host plant resistance, continuous efforts in the identification and deployment of new resistance genes are required to support the development of soybean cultivars with multiple and durable resistance to these pests.

Photosynthesis of soybean cultivars released in different decades after grafting onto record-yield cultivars as rootstocks

While photosynthesis of soybean has been enhanced by breeding, it remains to be clarified whether the improvement of root function could bring a further increase of photosynthetic capacity for the development of soybean cultivars. The objective of this grafting experiment was to determine the influence of record-yield soybean cultivars, Liaodou14 (L14) and Zhonghuang35 (Z35), as rootstocks on photosynthetic traits of cultivars released in different decades. Grafting of various soybean cultivars onto L14 or Z35 rootstocks showed a higher root physiological activity, which resulted in significant increases in some photosynthetic traits at the late grain-filling stage compared with the non-grafted and self-grafted plants. The genetic gain for some photosynthetic traits of cultivars released from 1966 to 2006 increased by using L14 and Z35 as rootstocks. It suggested that the photosynthetic traits of the recently released cultivars could increase more if their root functions are improved.

Comparative analysis of root transcriptomes from two contrasting drought-responsive Williams 82 and DT2008 soybean cultivars under normal and dehydration conditions.

The economically important DT2008 and the model Williams 82 (W82) soybean cultivars were reported to have differential drought-tolerant degree to dehydration and drought, which was associated with root trait. Here, we used 66K Affymetrix Soybean Array GeneChip to compare the root transcriptomes of DT2008 and W82 seedlings under normal, as well as mild (2 h treatment) and severe (10 h treatment) dehydration conditions. Out of the 38172 soybean genes annotated with high confidence, 822 (2.15%) and 632 (1.66%) genes showed altered expression by dehydration in W82 and DT2008 roots, respectively, suggesting that a larger machinery is required to be activated in the drought-sensitive W82 cultivar to cope with the stress. We also observed that long-term dehydration period induced expression change of more genes in soybean roots than the short-term one, independently of the genotypes. Furthermore, our data suggest that the higher drought tolerability of DT2008 might be attributed to the higher number of genes induced in DT2008 roots than in W82 roots by early dehydration, and to the expression changes of more genes triggered by short-term dehydration than those by prolonged dehydration in DT2008 roots vs. W82 roots. Differentially expressed genes (DEGs) that could be predicted to have a known function were further analyzed to gain a basic understanding on how soybean plants respond to dehydration for their survival. The higher drought tolerability of DT2008 vs. W82 might be attributed to differential expression in genes encoding osmoprotectant biosynthesis-, detoxification- or cell wall-related proteins, kinases, transcription factors and phosphatase 2C proteins. This research allowed us to identify genetic components that contribute to the improved drought tolerance of DT2008, as well as provide a useful genetic resource for in-depth functional analyses that ultimately leads to development of soybean cultivars with improved tolerance to drought.