Soybean Cyst Nematode HG Type Research Articles

Heterodera glycines HG type 1.2.5.7 causes a decrease in soybean (Glycine max [L.] Merr.) nitrogen fixation and growth variables

ABSTRACT Soybean cyst nematode (SCN), Heterodera glycines, HG type 1.2.5.7 is the most virulent and widespread SCN biotype in the southern states of the USA, but its effect on soybean (Glycine max [L.] Merr.) nitrogen fixation (NF) activity and growth is not well documented. The objectives of this study were to: (1) measure the impact of HG type 1.2.5.7 on NF activity during the early vegetative stage of three soybean genotypes and (2) compare the impact on soybean leaf and root development, and plant growth. The NF activity of two susceptible (S) genotypes (“Ellis” and “Williams 82”) and one resistant (R) genotype (PI 88,788), subjected to a 10,000-egg treatment, was measured using an in-situ flow-through acetylene reduction assay. The average NF activity of the soybean genotypes was decreased by SCN activity. Time points assessment showed that the NF activity was differently impacted among the genotypes. Based on the measured values, the NF activity was decreased by 30% in SCN infected plants of Williams 82 but that of PI 88,788 and Ellis was affected. Likewise, soybean leaf color and leaf area were affected by SCN infection, but there was no impact on root length and root area. These results showed that SCN HG type 1.2.5.7 can exhibit varying negative impact on NF and shoot growth of S soybean genotypes, while R genotypes may be unaffected. Thus, indicating genetic resistance continues to be a critical tool for the management of the SCN.

Development of a Standardized Soybean Cyst Nematode Screening Assay in Pennycress and Identification of Resistant Germplasm.

The prospect of incorporating pennycress as an oilseed cover crop in the Midwest's corn-soybean rotation system has drawn researcher and farmer attention. The inclusion of pennycress will be beneficial as it provides an excellent soil cover to reduce soil erosion and nutrient leaching while serving as an additional source for oilseed production and income. However, pennycress is an alternative host for soybean cyst nematode (SCN), which is a major biological threat to soybean that needs to be addressed for sustainable pennycress adoption into our current production systems. To develop a standardized SCN resistance screening strategy in pennycress, we tested and optimized five parameters: (i) germination stimulants, (ii) inoculation timing, (iii) inoculation rate, (iv) experimental incubation time, and (v) susceptible checks. The standardized SCN resistance screening protocol includes the following: (i) treating pennycress seeds with gibberellic acid for 24 h, (ii) transplanting seedlings 12 to 15 days after initiating germination and inoculating 10 to 12 days after transplantation, (iii) inoculating at a rate of 1,500 eggs/100 cc soil (1,500 eggs per plant), (iv) processing roots at 30 days after inoculation, and (v) using susceptible pennycress accession Ames 32869 to calculate the female index. The standardized protocol was used to quantify the response of a diverse set of pennycress accessions for response against SCN HG type 1.2.5.7 and HG type 7. While there were no highly resistant pennycress lines identified, 15 were rated as moderately resistant to HG type 1.2.5.7, and eight were rated moderately resistant to HG type 7. The resistant lines identified in this study could be utilized to develop SCN-resistant pennycress cultivars. The study also opens a new avenue for research to understand SCN-pennycress interactions through molecular and genomic studies. This knowledge could aid in the successful inclusion of pennycress as a beneficial cover/oilseed crop in the United States Midwest.[Formula: see text] Copyright © 2024 The Author(s). This is an open access article distributed under the CC BY-NC-ND 4.0 International license.

Cataloging SCN resistance loci in North American public soybean breeding programs.

Soybean cyst nematode (SCN) is a destructive pathogen of soybeans responsible for annual yield loss exceeding $1.5 billion in the United States. Here, we conducted a series of genome-wide association studies (GWASs) to understand the genetic landscape of SCN resistance in the University of Missouri soybean breeding programs (Missouri panel), as well as germplasm and cultivars within the United States Department of Agriculture (USDA) Uniform Soybean Tests-Northern Region (NUST). For the Missouri panel, we evaluated the resistance of breeding lines to SCN populations HG 2.5.7 (Race 1), HG 1.2.5.7 (Race 2), HG 0 (Race 3), HG 2.5.7 (Race 5), and HG 1.3.6.7 (Race 14) and identified seven quantitative trait nucleotides (QTNs) associated with SCN resistance on chromosomes 2, 8, 11, 14, 17, and 18. Additionally, we evaluated breeding lines in the NUST panel for resistance to SCN populations HG 2.5.7 (Race 1) and HG 0 (Race 3), and we found three SCN resistance-associated QTNs on chromosomes 7 and 18. Through these analyses, we were able to decipher the impact of seven major genetic loci, including three novel loci, on resistance to several SCN populations and identified candidate genes within each locus. Further, we identified favorable allelic combinations for resistance to individual SCN HG types and provided a list of available germplasm for integration of these unique alleles into soybean breeding programs. Overall, this study offers valuable insight into the landscape of SCN resistance loci in U.S. public soybean breeding programs and provides a framework to develop new and improved soybean cultivars with diverse plant genetic modes of SCN resistance.

Weighted gene co-expression network analysis identifies genes related to HG Type 0 resistance and verification of hub gene GmHg1.

The soybean cyst nematode (SCN) is a major disease in soybean production thatseriously affects soybean yield. At present, there are no studies on weighted geneco-expression network analysis (WGCNA) related to SCN resistance. Here, transcriptome data from 36 soybean roots under SCN HG Type 0 (race 3) stresswere used in WGCNA to identify significant modules. A total of 10,000 differentially expressed genes and 21 modules were identified, of which the module most related to SCN was turquoise. In addition, the hub gene GmHg1 with high connectivity was selected, and its function was verified. GmHg1 encodes serine/threonine protein kinase (PK), and the expression of GmHg1 in SCN-resistant cultivars ('Dongnong L-204') and SCN-susceptible cultivars ('Heinong 37') increased significantly after HG Type 0 stress. Soybean plants transformed with GmHg1-OX had significantly increased SCN resistance. In contrast, the GmHg1-RNAi transgenic soybean plants significantly reduced SCN resistance. In transgenic materials, the expression patterns of 11 genes with the same expression trend as the GmHg1 gene in the 'turquoise module' were analyzed. Analysis showed that 11genes were co-expressed with GmHg1, which may be involved in the process of soybean resistance to SCN. Our work provides a new direction for studying the Molecular mechanism of soybean resistance to SCN.

Quantitative trait loci and gene-specific markers associated with resistance to soybean cyst nematode HG type 2.5.7.

The online version contains supplementary material available at 10.1007/s11032-022-01330-8.

Reproduction of Soybean Cyst Nematode Populations on Field Pennycress, Henbit, and Purple Deadnettle Weed Hosts

Several weeds serve as alternative soybean cyst nematode (SCN) hosts. Still, the relative reproductive capacity of SCN HG types (Heterodera glycines type) on weed hosts relative to soybean is not well understood. This study examined the reproduction of three South Dakota endemic SCN populations—PSCN-1 (HG 0), PSCN-2 (HG 2.5.7), and PSCN-3 (HG 7)—on purple deadnettle, field pennycress, and henbit. The Relative Female Index (RFI) was calculated to compare SCN reproduction relative to the susceptible soybean check. Weed hosts, HG types, and their interactions influenced SCN reproduction. Henbit (RFI = 51.8) and purple deadnettle (RFI = 47.6) roots had a similar high RFI, whereas field pennycress (RFI = 23.04) had a lower RFI. Similarly, SCN populations PSCN-1 and PSCN-3 had a similar RFI of 36.9 and 37.2, respectively, while the population PSCN-2 had a higher RFI of 44.9 across weed hosts. A significant interaction between PSCN-1 and purple deadnettle was observed where the RFI was the highest (RFI = 53.3). These results indicate that these weed hosts support endemic SCN populations, and the HG type influenced reproductive success, further complicating SCN management. Hence, SCN presents a significant challenge in the new prospect of incorporating field pennycress host as an oilseed cover crop in the Midwest’s corn–soybean production system.

Breeding a Soybean Cultivar Heinong 531 with Peking-Type Cyst Nematode Resistance, Enhanced Yield, and High Seed-Oil Contents.

Soybean cyst nematode (SCN) is a destructive threat to soybean production. It is economically important to develop a new SCN-resistant soybean cultivar with high yield and other good agronomic traits. In this study, a yellow-seed-coated and yellow-hilum-pigmented cultivar Heinong 531 belonging to maturity group I was developed by a pedigree breeding method through a test-cross between a female parental SCN-resistant soybean cultivar Pengdou 158 and a male parental line F1 (high-yield but SCN-susceptible Hefeng 55 × SCN-resistant Kangxian 12). Heinong 531 was evaluated for SCN resistance in both SCN-infested field and autoclaved soil inoculated with hatched second-stage juveniles of SCN HG Type 0. The results indicated that SCN development at all stages in Heinong 531 was suppressed and the female index was only 1.6 to 5.6%. Heinong 531 as well as Pengdou 158 and Kangxian 12 were identified as carrying the Peking-type resistance with both rhg1-a GmSNAP18 and Rhg4 GmSHMT08 genes. In the 2-year regional trials, the average yield of Heinong 531 reached 2805.0 kg/ha, and the 1-year production trial demonstrated an average yield of 2,751.5 kg/ha with yield increase of >12.0% when compared with the local cultivars. The average seed-fat (oil) contents of Heinong 531 reached up to 22.3%. The Peking-type SCN-resistant Heilong 531 with enhanced yield and high seed-oil contents was released in China in June 2021 with the certified number of 'Heishendou 20210004'. These agronomic traits make Heinong 531 a good prospect in a wide attempt to control SCN in the main soybean-producing areas of Northeast China.

‘S16‐14730C’: A high‐yielding conventional soybean cultivar with indeterminate growth habit and multiple disease resistance adapted to the Mid‐South

Abstract‘S16‐14730C’ (Reg. no. CV‐546, PI 699632) is a conventional maturity group (MG) IV (relative maturity, 4.7) soybean [Glycine max (L.) Merr.] cultivar released by the University of Missouri–Fisher Delta Research Center breeding program in 2020. It has an indeterminate growth habit, averaging 89 cm in height with a 2.1 lodging score. Plants have purple flowers, tawny pubescence, and tan pod wall color, and seeds have black hilum and 402.8 g kg–1 of protein and 224.0 g kg–1 of oil concentrations. S16‐14730C underwent extensive yield testing and disease evaluation from 2017 to 2020 over a total of 104 environments across 12 states. During the USDA uniform trials in 2018 and 2019, S16‐14730C yielded 4,192 kg ha–1, equivalent to 99 and 108% of the best checks and overall check mean, respectively. S16‐14730C shows resistance to stem canker and soybean cyst nematode (SCN) HG type 2.5.7 (race 1) and HG type 5.7 (race 3) and moderate resistance to SCN HG type 1.2.5.7 (race 2), southern root‐knot nematode, peanut root‐knot nematode, and charcoal rot. It is susceptible to reniform nematode and phytophthora root rot. S16‐14730C may serve as an excellent choice in regions where a late MG IV conventional line is in demand.

Epistatic interaction between Rhg1-a and Rhg2 in PI 90763 confers resistance to virulent soybean cyst nematode populations

Key messageAn epistatic interaction between SCN resistance loci rhg1-a and rhg2 in PI 90763 imparts resistance against virulent SCN populations which can be employed to diversify SCN resistance in soybean cultivars.With more than 95% of the $46.1B soybean market dominated by a single type of genetic resistance, breeding for soybean cyst nematode (SCN)-resistant soybean that can effectively combat the widespread increase in virulent SCN populations presents a significant challenge. Rhg genes (for Resistance to Heterodera glycines) play a key role in resistance to SCN; however, their deployment beyond the use of the rhg1-b allele has been limited. In this study, quantitative trait loci (QTL) were mapped using PI 90763 through two biparental F3:4 recombinant inbred line (RIL) populations segregating for rhg1-a and rhg1-b alleles against a SCN HG type 1.2.5.7 (Race 2) population. QTL located on chromosome 18 (rhg1-a) and chromosome 11 (rhg2) were determined to confer SCN resistance in PI 90763. The rhg2 gene was fine-mapped to a 169-Kbp region pinpointing GmSNAP11 as the strongest candidate gene. We demonstrated a unique epistatic interaction between rhg1-a and rhg2 loci that not only confers resistance to multiple virulent SCN populations. Further, we showed that pyramiding rhg2 with the conventional mode of resistance, rhg1-b, is ineffective against these virulent SCN populations. This highlights the importance of pyramiding rhg1-a and rhg2 to maximize the impact of gene pyramiding strategies toward management of SCN populations virulent on rhg1-b sources of resistance. Our results lay the foundation for the next generation of soybean resistance breeding to combat the number one pathogen of soybean.

Registration of TN15‐4009 soybean germplasm with resistance to soybean cyst nematode, southern root knot nematode, and peanut root knot nematode

AbstractThe conventional (non‐genetically modified) soybean [Glycine max (L.) Merrill] line TN15‐4009 (Reg. no. GP‐437, PI 691608) was released by University of Tennessee Agricultural Research in 2019 as a germplasm line on the basis of its high seed yield potential in the southern region of the United States and resistance to soybean cyst nematode (SCN), southern root knot nematode, and peanut root knot nematode. The objective of its development was to create a high‐yielding SCN‐resistant soybean line. Progeny rows were selected based on adapted maturity, lodging resistance, disease resistance, and pod density and were entered in yield tests from 2015 through 2018. TN15‐4009 has white flowers and tawny pubescence. The pods have a tan pod wall, and the seed is yellow with a smooth seed coat. The seed size is approximately 13.6 g 100 seed−1, which was significantly greater than that of ‘Ellis’ in the 2018 USDA Uniform Test. In that test, TN15‐4009 matured 1 d earlier than Ellis and the same as ‘AG 4835’, indicating that the relative maturity of TN15‐4009 is approximately 4.8. Soybean line TN15‐4009 is resistant to SCN HG type 5.7 (score = 1) and HG type 2.5.7 (score = 1), resistant to southern root knot nematode (score = 1), and resistant to peanut root knot nematode (score = 1.3). TN15‐4009 is susceptible to stem canker.

Dissection of soybean populations according to selection signatures based on whole-genome sequences.

BackgroundDomestication and improvement processes, accompanied by selections and adaptations, have generated genome-wide divergence and stratification in soybean populations. Simultaneously, soybean populations, which comprise diverse subpopulations, have developed their own adaptive characteristics enhancing fitness, resistance, agronomic traits, and morphological features. The genetic traits underlying these characteristics play a fundamental role in improving other soybean populations.ResultsThis study focused on identifying the selection signatures and adaptive characteristics in soybean populations. A core set of 245 accessions (112 wild-type, 79 landrace, and 54 improvement soybeans) selected from 4,234 soybean accessions was re-sequenced. Their genomic architectures were examined according to the domestication and improvement, and accessions were then classified into 3 wild-type, 2 landrace, and 2 improvement subgroups based on various population analyses. Selection and gene set enrichment analyses revealed that the landrace subgroups have selection signals for soybean-cyst nematode HG type 0 and seed development with germination, and that the improvement subgroups have selection signals for plant development with viability and seed development with embryo development, respectively. The adaptive characteristic for soybean-cyst nematode was partially underpinned by multiple resistance accessions, and the characteristics related to seed development were supported by our phenotypic findings for seed weights. Furthermore, their adaptive characteristics were also confirmed as genome-based evidence, and unique genomic regions that exhibit distinct selection and selective sweep patterns were revealed for 13 candidate genes.ConclusionsAlthough our findings require further biological validation, they provide valuable information about soybean breeding strategies and present new options for breeders seeking donor lines to improve soybean populations.

Early transcriptional responses to soybean cyst nematode HG Type 0 show genetic differences among resistant and susceptible soybeans.

Root transcriptome profiling of three soybean cultivars and a wild relative infected with soybean cyst nematode at migratory phase revealed differential resistance pathway responses between resistant and susceptible genotypes. The soybean cyst nematode (SCN), Heterodera glycines, is the most serious pathogen of soybean production throughout the world. Using resistant cultivars is the primary management strategy against SCN infestation. To gain insight into the still obscure mechanisms of genetic resistance to nematodes in different soybean genotypes, RNA-Seq profiling of the roots of Glycine max cv. Peking, Fayette, Williams 82, and a wild relative (Glycine soja PI 468916) was performed during SCN infection at the migratory phase. The analysis showed statistically significant changes of expression beginning at eight hours after inoculation in genes associated with defense mechanisms and pathways, such as the phenylpropanoid biosynthesis pathway, plant innate immunity and hormone signaling. Our results indicate the importance of the early plant response to migratory phase nematodes in pathogenicity determination. The transcriptome changes occurring during early SCN infection included a number of genes and pathways specific to the different resistant genotypes. We observed the most extensive resistant transcriptome reaction in PI 468916, where the resistant response was qualitatively different from that of commonly used G. max varieties.

Genome-wide identification of soybean microRNA responsive to soybean cyst nematodes infection by deep sequencing

BackgroundThe soybean cyst nematode (SCN), Heterodera glycines, is one of the most devastating diseases limiting soybean production worldwide. It is known that small RNAs, including microRNAs (miRNAs) and small interfering RNAs (siRNAs), play important roles in regulating plant growth and development, defense against pathogens, and responses to environmental changes.ResultsIn order to understand the role of soybean miRNAs during SCN infection, we analyzed 24 small RNA libraries including three biological replicates from two soybean cultivars (SCN susceptible KS4607, and SCN HG Type 7 resistant KS4313N) that were grown under SCN-infested and -noninfested soil at two different time points (SCN feeding establishment and egg production). In total, 537 known and 70 putative novel miRNAs in soybean were identified from a total of 0.3 billion reads (average about 13.5 million reads for each sample) with the programs of Bowtie and miRDeep2 mapper. Differential expression analyses were carried out using edgeR to identify miRNAs involved in the soybean-SCN interaction. Comparative analysis of miRNA profiling indicated a total of 60 miRNAs belonging to 25 families that might be specifically related to cultivar responses to SCN. Quantitative RT-PCR validated similar miRNA interaction patterns as sequencing results.ConclusionThese findings suggest that miRNAs are likely to play key roles in soybean response to SCN. The present work could provide a framework for miRNA functional identification and the development of novel approaches for improving soybean SCN resistance in future studies.

Registration of ‘Agustina’ Soybean Cultivar

‘Agustina’ soybean [Glycine max (L.) Merr.] cultivar (Reg. No. CV‐524, PI 679941) was developed by the Clemson Pee Dee Research and Extension Center in Florence, SC. It was released in 2016 because of its ability to delay flowering under short‐day conditions and produce high yields, which is due in part to the long juvenile (LJ) trait. The LJ trait extends the period between germination and flowering under short‐day growing conditions. Thus, the latitude in which the cultivar is grown can have a large impact on maturity. When grown in Florence, SC, Agustina was tested as a maturity group (MG) VIII, high‐yielding, conventional (non‐genetically modified) cultivar. When tested ∼12° further south in Tampico, Mexico, Agustina was classified as a MG IX cultivar. In Tampico, (27° N), the furthest south it was tested, Agustina was the highest‐yielding line in the test, outyielding the highest‐yielding check by 222 kg ha−1. Agustina traces to a single plant selection in the F5 generation in 2010 from a cross between SC98‐1850 and ‘Manokin.’ Agustina exhibits white flowers, tawny pubescence, and an imperfect black hilum color. It has excellent resistance to soybean cyst nematode HG type 2.5.7 (race 1) and HG type 0 (race 3) and moderate resistance to HG type 2.5.7(race 5). Agustina is a highly versatile cultivar that performs well across multiple environments.

Loci and candidate genes conferring resistance to soybean cyst nematode HG type 2.5.7

BackgroundSoybean (Glycine max L. Merr.) cyst nematode (SCN, Heterodera glycines I,) is a major pest of soybean worldwide. The most effective strategy to control this pest involves the use of resistant cultivars. The aim of the present study was to investigate the genome-wide genetic architecture of resistance to SCN HG Type 2.5.7 (race 1) in landrace and elite cultivated soybeans.ResultsA total of 200 diverse soybean accessions were screened for resistance to SCN HG Type 2.5.7 and genotyped through sequencing using the Specific Locus Amplified Fragment Sequencing (SLAF-seq) approach with a 6.14-fold average sequencing depth. A total of 33,194 SNPs were identified with minor allele frequencies (MAF) over 4%, covering 97% of all the genotypes. Genome-wide association mapping (GWAS) revealed thirteen SNPs associated with resistance to SCN HG Type 2.5.7. These SNPs were distributed on five chromosomes (Chr), including Chr7, 8, 14, 15 and 18. Four SNPs were novel resistance loci and nine SNPs were located near known QTL. A total of 30 genes were identified as candidate genes underlying SCN resistance.ConclusionsA total of sixteen novel soybean accessions were identified with significant resistance to HG Type 2.5.7. The beneficial alleles and candidate genes identified by GWAS might be valuable for improving marker-assisted breeding efficiency and exploring the molecular mechanisms underlying SCN resistance.

Increase in Soybean Cyst Nematode Virulence and Reproduction on Resistant Soybean Varieties in Iowa From 2001 to 2015 and the Effects on Soybean Yields

Management of the soybean cyst nematode (SCN) relies heavily on use of SCN-resistant soybean varieties to limit nematode reproduction and minimize yield loss. For Iowa, almost all SCN-resistant soybean varieties contain SCN resistance genes from a breeding line named Plant Introduction (PI) 88788. Iowa State University conducts experiments to evaluate numerous SCN-resistant and three to four SCN-susceptible soybean varieties in up to nine field experiments across Iowa each year. Data on SCN population density, virulence (SCN race and HG type), soybean yield, precipitation, and growing degree days from more than 25,000 four-row plots in field experiments conducted from 2001 to 2015 were analyzed to determine how these factors affected SCN reproduction and yield. SCN population densities were positively correlated with temperatures and negatively associated with precipitation during the growing seasons, indicating that SCN reproduction was greatest in hot, dry years. Over the years, virulence of SCN populations on PI 88788 increased in the fields in which the experiments were conducted, resulting in increased end-of-season SCN population densities and reduced yields of SCN-resistant soybean varieties with the PI 88788 source of resistance. These results indicate that soybean yield loss caused by SCN on resistant varieties with the common PI 88788 source of resistance likely will increase as virulence of SCN populations increases unless new sources of resistance become widely available and used in the future.

Identification of Loci Underlying Seed Yield in Recombinant Inbred and Near Isogeneic Soybean Lines Derived from Flyer by Hartwig

Two major determinants of soybean [Glycine max (L.) Merr.] seed yield were resistances to the soybean cyst nematode (SCN) and sudden death syndrome (SDS). Two loci were identified rhg1/Rfs2 and rhg3/rfs5 (for resistance to SCN, Heterodera glycines (I.) HG Type 1.3- (race 14), HG Type 0 (race 3) and SDS caused by Fusarium virguliforme (Roy & Rupe)). The aim of this study was to identify quantitative trait loci (QTL) underlying seed yield. Used were 142 microsatellite markers and the recombinant inbred line population (RIL) ‘Flyer’ × ‘Hartwig’ (F × H; n=92). Flyer (F) was high yielding but SCN and SDS susceptible. Hartwig (H) was lower yielding but resistant to all SCN Hg Types and SDS. Four regions on 3 chromosomes were associated with seed yield. The first region on chromosome 9 (Gm9, qYld09.1), identified by the microsatellite marker Satt539-Satt242 (LOD 2.9, 13% variation) derived the beneficial allele from Hartwig (F allele 2.76 ± 0.06 Mg/Ha; H allele 2.98 ± 0.03 Mg/ha). The second region on Gm9 (qYld09.2) between Satt337 and Satt326 spanned 1.4 cM (LOD of 5.31, 20.2% variation) and the beneficial allele derived from Flyer (0.22 Mg/ha F allele 2.98 ± 0.03, H allele 2.77 ± 0.04 Mg/Ha). The third and fourth QTL were identified in genetic linkage groups D2 (qYld19.1) and G (qYld18.1) in regions previously associated with resistance to SCN. The region encompassing rhg1/Rfs2 on Gm18 between the microsatellite marker TMD1 and Satt610 spanned 15.5 cM (LOD 3.05, 15.8 % variation, F allele 2.37 ± 0.035; H allele 2.91 ± 0.058 Mg/Ha). The region on linkage group D2 between Satt514 and Satt488 spanned 32.6 cM (LOD 2.57, Kas13.3% variation, F allele 2.79 ± 0.049; H allele 3.1 ± 0.043 Mg/Ha). The QTL detected will allow marker assisted selection to stack seed yield, with pest resistance traits (rhg1/Rfs2/qYld18.1; H/H/H allele) and recombinant loci (Rhg5/Rfs2/qYld19.1; H/F/H alleles).

Determination of Heterodera glycines Virulence Phenotypes Occurring in South Dakota.

The soybean cyst nematode (SCN), Heterodera glycines, is the most important yield-limiting pathogen of soybean in the United States. In South Dakota, SCN has been found in 29 counties, as of 2016, and continues to spread. Determining the virulence phenotypes (HG types) of the SCN populations can reveal the diversity of the SCN populations and the sources of resistance that would be most effective for SCN management. To determine the HG types prevalent in South Dakota, 250 soil samples were collected from at least three arbitrarily selected fields in each of the 28 counties with fields previously found to be infested with SCN. SCN was detected in 82 fields (33%), and combined egg and juvenile counts ranged from 200 to 65,200 per 100 cm3 of soil. Eggs and juveniles were extracted from each soil sample and were used to infest seven SCN HG type test indicator soybean lines and 'Williams 82' as the susceptible check. A female index (FI) was calculated based on the number of females found on each indicator line relative to those on the susceptible check. A FI equal to or greater than 10% in any line was assigned as that HG type. Out of 73 SCN populations for which HG type tests were done, 63% had FI ≥10% on PI 548316 (indicator line #7), 25% on PI 88788 (#2), 19% on PI 209332 (#5), 7% on PI 548402 (#1), 4% on PI 90736 (#3), and 4% on PI 89722 (#6). None of the SCN populations had FI ≥10% on PI 437654 (indicator line #4). The most prevalent HG types were 0, 2.5.7, and 7. These accounted for 81% of all the HG types determined for the samples tested. HG types with ≥10% reproduction on indicator lines PI 88788, PI 209332, and PI 548317 were most prevalent in the soil samples tested, suggesting that the use of these sources of resistance for developing SCN resistant cultivars should be avoided. For sustainable SCN management, use of resistant cultivars should be rotated with nonhost crops and cultivars with different sources of resistance.

Genome-Wide Association Study of Resistance to Soybean Cyst Nematode (Heterodera glycines) HG Type 2.5.7 in Wild Soybean (Glycine soja).

Soybean cyst nematode (SCN) is the most destructive soybean pest worldwide. Host plant resistance is the most environmentally friendly and cost-effective way of mitigating SCN damage to soybeans. However, overuse of the resistant soybean [Glycine max (L.) Merr.] cultivars from limited genetic resources has resulted in SCN race shifts in many soybean-growing areas. Thus, exploration of novel sources of SCN resistance and dissection of the genetic basis are urgently needed. In this study, we screened 235 wild soybean (Glycine soja Sieb. & Zucc.) accessions to identify genotypes resistant to SCN HG Type 2.5.7 (race 5), a less investigated type but is prevalent in the southeastern US. We also dissected the genetic basis of SCN resistance using a genome-wide association study with SNPs genotyped by SoySNP50k iSelect BeadChip. In total, 43 resistant accessions (female index < 30) were identified, with 10 SNPs being significantly associated with SCN HG 2.5.7 resistance in this wild species. Furthermore, four significant SNPs were localized to linked regions of the known quantitative trait locus (QTL) rhg1 on chromosome 18. The other four SNPs on chromosome 18 and two SNPs on chromosome 19 are novel. Genes encoding disease resistance-related proteins with a leucine-rich region, a mitogen-activated protein kinase (MAPK) on chromosome 18, and a MYB transcription factor on chromosome 19 were identified as promising candidate genes. The identified SNPs and candidate genes will benefit future marker-assisted breeding and dissection of the molecular mechanisms underlying the soybean-SCN interaction.

Transgenic soybean overexpressing GmSAMT1 exhibits resistance to multiple-HG types of soybean cyst nematode Heterodera glycines.

SummarySoybean (Glycine max (L.) Merr.) salicylic acid methyl transferase (GmSAMT1) catalyses the conversion of salicylic acid to methyl salicylate. Prior results showed that when GmSAMT1 was overexpressed in transgenic soybean hairy roots, resistance is conferred against soybean cyst nematode (SCN), Heterodera glycines Ichinohe. In this study, we produced transgenic soybean overexpressing GmSAMT1 and characterized their response to various SCN races. Transgenic plants conferred a significant reduction in the development of SCN HG type 1.2.5.7 (race 2), HG type 0 (race 3) and HG type 2.5.7 (race 5). Among transgenic lines, GmSAMT1 expression in roots was positively associated with SCN resistance. In some transgenic lines, there was a significant decrease in salicylic acid titer relative to control plants. No significant seed yield differences were observed between transgenics and control soybean plants grown in one greenhouse with 22 °C day/night temperature, whereas transgenic soybean had higher yield than controls grown a warmer greenhouse (27 °C day/23 °C night) temperature. In a 1‐year field experiment in Knoxville, TN, there was no significant difference in seed yield between the transgenic and nontransgenic soybean under conditions with negligible SCN infection. We hypothesize that GmSAMT1 expression affects salicylic acid biosynthesis, which, in turn, attenuates SCN development, without negative consequences to soybean yield or other morphological traits. Thus, we conclude that GmSAMT1 overexpression confers broad resistance to multiple SCN races, which would be potentially applicable to commercial production.