Soybean Cyst Nematode Population Research Articles

Fortifying nematode resistance through susceptibility gene inactivation

The predominant genetic defense mechanism against soybean cyst nematode (SCN) in 95% of the North America market is under threat by virulent SCN populations. Usovsky et al. identified GmSNAP02 as an SCN susceptibility gene through fine-mapping of unique bi-parental populations. Loss-of-function of GmSNAP02 confers enhanced resistance to more virulent SCN.

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.

Chemical Profiles of Heterodera glycines Suppressive Soils in Double Cropping Soybean Production.

We previously reported soybean fields double-cropped with winter wheat having reduced soybean cyst nematode (SCN) (Heterodera glycines) counts compared to fallow. A follow-up metagenomics study identified several fungal and bacterial taxa enriched in wheat fields, and some were reported to parasitize SCN. Knowing that phytocompounds with potential nematicidal activity are released via wheat roots and stubble, we implemented a dichloromethane-based extraction method and a gas chromatography-mass spectrometry (GCMS) system to investigate soil chemical profiles of samples collected from these fields and review the potential nematicidal activity of compounds with higher concentration in double cropping fields. 51 compounds were detected during the GCMS analysis, eight with unknown identification. Several compounds, including multiple fatty acids, had larger relative peak areas when double-cropped, compared to fallow samples. This study, along with our previously published one, provided a better understanding of the mechanisms that govern the effect of wheat on SCN populations. Rather than driven by a single mechanism, the suppression of SCN in soybean fields double-cropped with winter wheat was potentially linked to enriched microbial communities, increased populations of beneficial organisms, and higher concentrations of chemicals with potential nematicidal activity. To our knowledge, this is the first study using GCMS to characterize soil chemical profiles in soybean fields double-cropped with winter wheat regarding the suppression of SCN populations.

Seed Treatments for Management of Soybean Cyst Nematode, Heterodera glycines, in Mid-Atlantic Soybean Production.

Soybean Cyst Nematode (SCN), Heterodera glycines Ichinohe, is the most important pathogen of soybean in the Mid-Atlantic region. In recent decades, a decline in the effectiveness of genetic resistance has been observed and additional management approaches are needed. Seed treatments are of rising interest, but no local data on product response exists for the region. In 2020-2021, two experiments were conducted to observe the effects of chemical and biological seed treatment options. In one experiment, chemical seed treatments pydiflumetofen (Saltro®) and fluopyram (ILEVO®) were screened against nontreated plain seed for SCN suppression. In a second experiment, pydiflumetofen, fluopyram and four biological nematode-protectant seed treatments with a standard base insecticide and fungicide treatment were compared to nontreated plain seed and seed with only the standard base treatment to test product efficacy against SCN. Seed treatments increased the percent emergence over plain seed. Nematode reproductive factors and female counts from roots were collected, but did not statistically differ between seed treatments or plain seed. Yield differences were observed in one of the five trials, where pydiflumetofen + base seed treatment yielded the highest (p < 0.001) at 3813.1 kg/ha. Response from seed treatments varied, with no specific seed treatment consistently reducing SCN populations or increasing yield across trials. Seed treatments may have potential as an element of an integrated management approach for SCN.

Interactions Among Heterodera glycines, Macrophomina phaseolina, and Soybean Genotype.

Heterodera glycines, the soybean cyst nematode (SCN), and fungal pathogen Macrophomina phaseolina are economically important soybean pathogens that may coinfest fields. Resistance remains the most effective management tactic for SCN, and the rhg1-b resistance allele derived from plant introduction 88788 is most commonly deployed in the northern United States. The concomitant effects of SCN and M. phaseolina on soybean performance, as well as the effect of the rhg1-b allele in two different genetic backgrounds, were evaluated in three environments (during 2013 to 2015) and a greenhouse bioassay. Within two soybean populations, half of the lines had the rhg1-b allele, and the other half had the susceptible allele in the backgrounds of the cultivars IA3023 and LD00-3309. Significant interactions between soybean rhg1-b allele and M. phaseolina-infested plots were observed in 2014. In all experiments, initial SCN populations (Pi) and M. phaseolina in roots were associated with reduced soybean yield. SCN reproduction factor (RF = final population/Pi) was affected by SCN Pi, rhg1-b, and genetic background. A background-by-genotype interaction on yield was observed only in 2015, with a stronger rhg1-b effect in the LD00-3309 background, which suggested that the susceptible parent 'IA3023' is tolerant to SCN. SCN female index from greenhouse experiments was compared with field RF, and Lin's concordance and Pearson's correlation coefficients decreased with increasing field SCN Pi in soil. In this study, both SCN and M. phaseolina reduced soybean yield asymptomatically, and the impact of SCN rhg1-b resistance was dependent on SCN virulence but also population density.

Frequency of Occurrence of Heterodera glycines Types, Meloidogyne spp., and Eight Other Nematode Taxa Associated with Soybeans in Georgia

Soybean fields in Georgia were surveyed for plant-parasitic nematodes (PPNs) during the 2021 growing season. The frequency and population density of 10 PPN taxa were determined in 144 soil samples collected from soybean fields in 31 Georgia counties. Between one and six PPN taxa were identified in 97% of the soil samples, with &gt;50% of samples harboring four or more taxa. The spiral nematode ( Helicotylenchus spp.) was the most prevalent (85%), followed by lesion ( Pratylenchus spp., 71%), stubby root (Trichodoridae, 69%), ring (Criconematidae, 54%), root-knot ( Meloidogyne spp., 49%), stunt ( Tylenchorhynchus spp., 11%), reniform ( Rotylenchulus spp., 8%), cyst (Heteroderidae, 8%), dagger ( Xiphinema spp., 4%), and lance ( Hoplolaimus spp., 2%). Fourteen soil samples from nine Georgia counties were confirmed to have the soybean cyst nematode (SCN), Heterodera glycines (HG), based on morphological identification, molecular identification, and evidence of reproduction on soybean. HG type tests determined the virulence of each SCN population on resistant soybean. All SCN populations tested were able to reproduce at a female index ≥ 10% on PI 88788. HG type 1.2.- was the most frequent (57%), followed by HG type 2.- (29%) and HG type 1.2.3.- (14%). Meloidogyne incognita was the most frequently identified species of root-knot nematode (80%), followed by M. arenaria (28%) and M. javanica (6%). Our survey results serve to raise awareness of PPNs among Georgia soybean producers to inform future management decisions and improve information available to soybean breeders in their efforts to incorporate multiple nematode resistance into improved soybean cultivars.

A Survey of Soybean Cyst Nematode Population Densities and Phenotypes in Illinois: 2018 and 2020

In Illinois, soybean cyst nematode (SCN; Heterodera glycines) has been estimated to cause over $15 million in losses as recently as 2021. In addition, populations of SCN insensitive to PI 88788-derived resistance, the most commonly used SCN resistance source in commercially available soybeans, continues to increase in soybean production areas in the United States. Despite this, awareness of this pathogen and its current status in the state is relatively lacking. A survey was conducted in 2018 and 2020 to assess the presence, population level, and virulence phenotypes in Illinois soybean fields. Soil samples were collected and processed for SCN eggs after harvest each year, and samples with sufficient numbers of SCN eggs were virulence tested using the Hg type test. A total of 95 samples were collected, representing 46 counties. Eighty-seven percent of fields sampled contained SCN eggs, with 38% containing population densities over 2,000 eggs/100 cm3. All samples included in the Hg type test had a female index &gt; 10 on indicator line PI 88788, indicating insensitivity to this resistance source. Extrapolated across soybean production acres, these data indicate that approximately 4.4 million acres of soybeans contain levels of SCN requiring SCN management, and over 54% of acres using cultivars derived from PI 88788 are not fully protected from this pathogen.

Fluopyram activates systemic resistance in soybean

The soybean cyst nematode (SCN) (Heterodera glycines Ichinohe) is a significant yield-limiting factor in soybean production in the Midwestern US. Several management practices are implemented to mitigate yield losses caused by SCN, including using SDHI (succinate dehydrogenase inhibitors) fungicides delivered as seed treatments. A set of studies was conducted to evaluate the effect of two seed-applied succinate dehydrogenase inhibitors (SDHI) compounds, fluopyram and pydiflumetofen, on SCN population densities, plant injury, and plant growth. Cyst counts in untreated control and pydiflumetofen treated plants were 3.44 and 3.59 times higher than fluopyram, respectively, while egg counts were 8.25 and 7.06 times higher in control and pydiflumetofen. Next-generation sequencing was later employed to identify transcriptomic shifts in gene expression profiles in fluopyram and pydiflumetofen -treated seedlings. RNA expression patterns of seed treatments clustered by sampling time (5 DAP vs. 10 DAP); therefore, downstream analysis was conducted by timepoint. At 5 DAP, 10,870 and 325 differentially expressed genes (DEG) were identified in fluopyram and pydiflumetofen, respectively. These same treatments generated 219 and 2 DEGs at 10 DAP. Multiple DEGs identified in soybean seedlings treated with fluopyram are linked to systemic resistance, suggesting a potential role of systemic resistance in the suppression of SCN by fluopyram, in addition to the known nematicidal activity. The non-target inhibition of soybean succinate dehydrogenase genes by fluopyram may be the origin of the phytotoxicity symptoms observed and potentially the source of the systemic resistance activation reported in the current study. This work helps to elucidate the mechanisms of suppression of SCN by fluopyram.

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.

The Spatial Distribution and Genetic Diversity of the Soybean Cyst Nematode, Heterodera glycines, in China: It Is Time to Take Measures to Control Soybean Cyst Nematode.

The continuous evolution and spread of virulent forms of the soybean cyst nematode (SCN) driven by the environment and anthropogenic intervention is a serious threat to the soybean production worldwide, including China. Especially in China, the implemented measures to control SCN are insufficient for sustainable agricultural development yet. We summarized our knowledge about the spread and spatial distribution of SCN in China and the virulence diversity in the main soybean growing areas. To reveal the genetic relatedness and diversity of SCN populations, we re-sequenced 53 SCN genomes from the Huang-Huai Valleys, one of the two main soybean growing areas in China. We identified spreading patterns linked to the local agroecosystems and topographies. Moreover, we disclosed the first evidence for the selection of complex virulence in the field even under low selection pressure in an example from North Shanxi. SCN is present in all soybean growing areas in China but SCN susceptible cultivars are still largely grown indicating that SCN-related damage and financial loss have not received the attention they deserve yet. To prevent increasing yield losses and to improve the acceptance of resistant cultivars by the growers, we emphasized that it is time to accelerate SCN resistance breeding, planting resistant cultivars to a larger extent, and to support farmers to implement a wider crop rotation for sustainable development of the soybean production in China.

Exploring Soybean Resistance to Soybean Cyst Nematode.

Resistance to the soybean cyst nematode (SCN) is a topic incorporating multiple mechanisms and multiple types of science. It is also a topic of substantial agricultural importance, as SCN is estimated to cause more yield damage than any other pathogen of soybean, one of the world's main food crops. Both soybean and SCN have experienced jumps in experimental tractability in the past decade, and significant advances have been made. The rhg1-b locus, deployed on millions of farm acres, has been durable and will remain important, but local SCN populations are gradually evolving to overcome rhg1-b. Multiple other SCN resistance quantitative trait loci (QTL) of proven value are now in play with soybean breeders. QTL causal gene discovery and mechanistic insights into SCN resistance are contributing to both basic and applied disciplines. Additional understanding of SCN and other cyst nematodes will also grow in importance and lead to novel disease control strategies.

Assessing Direct and Residual Effects of Cover Crops on the Soybean Cyst Nematode, Heterodera glycines.

Greenhouse experiments were conducted to determine if cover crops directly decrease population densities of the soybean cyst nematode (SCN), Heterodera glycines, and/or have residual effects on reproduction of the nematode on soybean (Glycine max). Population densities of SCN were not significantly decreased by nine cover crop plants or three cover crop mixes compared with a non-planted soil control in a repeated 60-day-long greenhouse experiment. When susceptible soybeans were grown in the soils after cover crop growth, fewer SCN females formed after three annual ryegrass (Lolium multiflorum) cultivars (Bounty, King, and RootMax), the Daikon radish (Raphanus sativus var. longipinnatus) cultivar CCS779, Kodiak mustard (Brassica juncea), and a mix containing cereal rye, crimson clover (Trifolium incarnatum), plus Daikon radish (cultivars not stated) compared with following the non-planted control. In another repeated experiment, cover crops were grown for 56 days in SCN-infested soil in the greenhouse then exposed to Iowa winter conditions for 28 days to simulate winter termination of the plants. One treatment, a cover crop mix containing 'Bounty' annual ryegrass plus 'Enricher' Daikon radish, had a decrease in SCN population density greater than the non-planted control at the end of the experiment. Significantly fewer SCN females formed on soybeans grown after several cover crops, including the three annual ryegrass cultivars that had the suppressive residual effects in the first experiment. In summary, there were no cover crop treatments that consistently decreased SCN population densities across experiments, and only one cover crop treatment in one experiment significantly reduced SCN population densities more than a non-planted soil control. However, there was a somewhat consistent, adverse, residual effect of cover crops on reproduction of SCN on susceptible soybeans after growth of multiple cover crops.

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.

Examining the Interaction between Phytophthora sojae and Soybean Cyst Nematode on Soybean (Glycine max).

Phytophthora sojae and soybean cyst nematode (SCN) are important pathogens of soybean. Although these pathogens infect soybean roots, there is limited evidence of any interaction between them. The objective of this study was to examine the interaction between SCN and P. sojae on soybean in the greenhouse. Seeds of four soybean cultivars (Jack, Surge, Williams 82, Williams) were pre-germinated and placed in cone-tainers (Stuewe and Sons Inc., Tangent, OR, USA), containing a steam pasteurized sand-clay mixture. The experiment was set up in a completely randomized design with five replications and performed twice. Two P. sojae isolates were used in this study that represented two different virulence pathotypes (simple and complex pathotypes). For each isolate, soybean plants were not inoculated, inoculated with one of the treatments—SCN, P. sojae, and combination of P. sojae and SCN. After 35 DOI, stem length, root length, plant weight, root weight, lesion length, and SCN population were recorded. On all soybean cultivars with different types of incomplete resistance, the complex pathotype (PS-15-TF3) influenced the lesion length (mm) in the presence of SCN. However, the SCN population was reduced by both complex and simple pathotypes of P. sojae. This suggests that use both SCN and P. sojae resistance cultivars, can manage the disease complex and reduce soybean yield loss.

Soybean Cyst Nematode Population Development and its Effect on Pennycress in a Greenhouse Study.

Midwest crop production is dominated by two summer annual crops grown in rotation, viz., corn (Zea mays L.) and soybean (Glycine max L.). Winter oilseed crops, such as pennycress (Thlaspi arvense L.), can provide ecosystem and economic benefits when added to the corn–soybean rotation. However, adding a new crop adds risks, such as increased pest pressure. The objectives of this study were to (i) evaluate population development of three soybean cyst nematode (SCN; Heterodera glycines) biotypes on three pennycress genotypes and susceptible soybean and (ii) determine whether SCN inoculation level influenced plant biomass. SCN population density and biomass were determined after 60 d in the greenhouse. At the inoculation level of 2,000 eggs/100 cm3 soil, the average egg density for the three pennycress genotypes was 1,959 eggs/100 cm3 soil, lower than that for the susceptible soybean ‘Sturdy’ (9,601 eggs/100 cm3 soil). At the inoculation level of 20,000 eggs/100 cm3 soil, the average egg density for the three pennycress genotypes was 6,668 eggs/100 cm3 soil, lower than that for ‘Sturdy’ (40,740 eggs/100 cm3 soil). The inoculation level did not affect plant biomass. Pennycress is an alternative host to SCN under greenhouse conditions but is a less suitable host than soybean.

Interactive Effects of Soybean Cyst Nematode, Arbuscular-Mycorrhizal Fungi, and Soil pH on Chlorophyll Content and Plant Growth of Soybean

Nutritional deficiency chlorosis, especially iron-deficiency chlorosis, and the soybean cyst nematode (SCN) limit soybean yield. Arbuscular mycorrhizal fungi (MF) generally have beneficial effects on plant growth. The interactive effects of SCN, MF, and soil pH on leaf chlorophyll content (LCC) and growth of soybean were examined in a greenhouse experiment. The experiment was a randomized complete block design with three factors: SCN population densities, MF inoculation, and soil pH levels. SCN reduced LCC, and the effect increased with increasing time during 5 to 9 weeks after planting, especially in the high-pH (pH 8) soil. MF increased LCC in low-pH (pH 5.6) soil regardless of SCN population density and in the high-pH soil without SCN. However, MF reduced LCC if both pH and SCN population density were high. The high-SCN population density (inoculation with 10,000 eggs per 100 cm3 of soil) reduced soybean shoot weight in all soils regardless of MF. MF increased shoot weight at pH 6.9 and pH 8 but not at pH 5.6. When MF was present, shoot weight was generally highest at pH 6.9. At high SCN when MF was absent, plant growth was better in pH 5.6 than pH 6.9 and pH 8 soils. This study demonstrates that SCN causes greater damage to soybean when interacting with high pH, and MF had a beneficial effect on soybean growth regardless of SCN infection in all pH soils, in spite of the negative effect of MF on LCC at approximately 5 to 9 weeks after planting in high-pH soil at high SCN population density.

Registration of ‘TN14‐5021’, a conventional soybean cultivar with elevated seed protein and resistance to soybean cyst nematode races 2, 3, and 5

Abstract‘TN14‐5021’ (Reg. no. CV‐543, PI 699124) is a late maturity group IV (relative maturity 4.9) determinate conventional soybean [Glycine max (L.) Merr.] cultivar developed and released by the University of Tennessee soybean breeding program. Soybean cultivars with resistance to soybean cyst nematode (SCN) race 2 are rare, but race 2 is becoming a predominant SCN population infecting farmers’ fields in regions of the U.S. Southeast and Mid‐South. TN14‐5021 also conveys resistance to stem canker [caused by Diaporthe phaseolorum (Cooke &amp; Ellis) Sacc. var. caulivora K.L. Athow &amp; R.M. Caldwell] and strong resistance to SCN races 3 and 5. In replicated trials across 70 environments from the Mid‐South to the Southeast, TN‐5021 showed high yield potential and adaptation to a broad range of growing conditions. TN14‐5021 has white flowers and gray pubescence. The pods have a tan pod coat, and the seeds are yellow with smooth seed coats. Across 48 environments over a 4‐yr period, with testing locations from Kansas to Alabama, TN14‐5021 averaged 406 and 226 g kg–1 protein and oil content, respectively. In comparison, the average protein and oil content of commercial cultivars grown in the same tests averaged 397 and 224 g kg–1, respectively. Its high yield coupled with elevated seed protein concentration and nematode resistance package make TN14‐5021 a valuable cultivar for Tennessee and the Mid‐South region.

Soybean cyst nematode (Heterodera glycines) resistant cultivar rotation system impacts nematode population density, virulence, and yield

Soybean cyst nematode (SCN) is the most economically important pathogen of soybeans in the United States. The most effective SCN management practice is the use of resistant cultivars; however, continuous use of cultivars derived from a single line of resistance results in selection for SCN virulent populations. A four-year field study (2017–2020) was conducted in Michigan to evaluate the impact of six soybean rotation systems with cultivars derived from PI548402 (5DV) and PI88788 (8DV) on SCN population development, virulence, and soybean yield. The rotation systems were: 1) 8DV/5DV/8DV/5DV, 2) 5DV/5DV/5DV/5DV, 3) 8DV/Susceptible (SDV)/5DV/8DV, 4) 5DV/SDV/8DV/5DV, 5) 8DV/8DV/8DV/8DV, and 6) 5DV/SDV/SDV/SDV. SCN population levels were significantly lower in the 5DV/8DV rotation in 2018 compared to the 5DV/SDV rotation. In 2020, SCN population levels were the lowest in the rotation system 8DV/5DV/8DV/5DV and the highest in the continuous 5DV soybeans. In 2017, there were no substantial soybean yield differences among the differing systems, but for the remainder of the trial, the 5DV/8DV rotations had the highest yields. HG type tests showed that rotation of resistance sources can alter the virulence of the SCN population. The initial 2017 SCN population was HG type 1.2. The final populations in 2020 for the rotation systems 8DV/5DV/8DV/5DV, 5DV/5DV/5DV/5DV, and 8DV/SDV/5DV/8DV was HG type 1.2.5.7, and HG type 1.2.3.5.6.7 for the other rotation systems 5DV/SDV/8DV/5DV, 8DV/8DV/8DV/8DV, and 5DV/SDV/SDV/SDV. Based on the results of the field trial, a greenhouse trial was conducted where we found that a Michigan SCN population from continuous PI88788 sources of resistance can also reproduce on Peking. These findings indicate rotating PI548402- and PI88788-derived cultivars can reduce SCN density and maintain high soybean yields; thus rotating these two sources of resistance with non-host rotations might delay the aggressiveness of SCN populations further, reducing soybean yield loss.

Evaluation of Scopoletin from Penicillium janthinellum Snef1650 for the Control of Heterodera glycines in Soybean.

Soybean cyst nematode (SCN) (Heterodera glycines Ichinohe) is responsible for causing a major soybean disease globally. The fungal strain Penicillium janthinellum Snef1650 was evaluated against H. glycines. However, the effective determinants of the P. janthinellum strain are unknown. By performing pot experiments, a functioning compound was isolated from P. janthinellum Snef1650 through organic solvent extraction, semi-preparative HPLC, Sephadex LH-20 column chromatography, and silica gel column chromatography, and the isolated compound was identified to be scopoletin through 1H NMR, 13C NMR, and HPLC–MS. The pot experiments indicated that the treatment of soybean seeds with scopoletin drastically reduced the SCN population. The field experiments performed in 2017 and 2018 revealed that scopoletin decreased over 43.7% juveniles in the roots and over 61.55% cysts in the soil. Scopoletin treatment also promoted soybean growth and improved its yield, with an increase in plot yield by >5.33%. Scopoletin obtained from P. janthinellum Snef1650 could be used as an anti-H. glycines biocontrol agent.

Resistance Gene Pyramiding and Rotation to Combat Widespread Soybean Cyst Nematode Virulence

Soybean cyst nematode (SCN) is an important pathogen of soybean causing >$1 billion in yield losses annually in the United States. Planting SCN-resistant soybean cultivars is the primary management strategy. Resistance genes derived from the plant introduction (PI) 88788 (rhg1-b) and PI 548402 (Peking; rhg1-a and Rhg4) are the main types of resistance available in commercial cultivars. The PI 88788 rhg1-b resistance allele is found in the majority of SCN-resistant cultivars in the north central United States. The widespread use of PI 88788 rhg1-b has led to limited options for farmers to rotate resistance sources to manage SCN. Consequently, overreliance on a single type of resistance has resulted in the selection of SCN populations that have adapted to reproduce on these resistant cultivars. Here we evaluated the effectiveness of rotating soybean lines with different combinations of resistance genes to determine the best strategy for combating the widespread increase in virulent SCN and limit future nematode adaptation to resistant cultivars. Eight SCN populations were developed by continuous selection of a virulent SCN field population (Heterodera glycines [HG] type 1.2.5.7) on a single resistance source or in rotation with soybean pyramiding different resistance gene alleles derived from PI 88788 (rhg1-b), PI 437654 (rhg1-a and Rhg4), PI 468916 (cqSCN-006 and cqSCN-007), and PI 567516C (Chr10). SCN population densities were determined for eight generations. HG type tests were conducted after the eighth generation to evaluate population shifts. The continued use of rhg1-b or 006/007 had limited effectiveness for reducing SCN type 1.2.5.7 population density, whereas rotation to the use of rhg1-a/Rhg4 resistance significantly reduced SCN population density but selected for broader SCN virulence (HG type 1.2.3.5.6.7). A rotation of rhg1-a/Rhg4 with a pyramid of rhg1-b/006/007/Chr10 was the most effective combination at both reducing population density and minimizing selection pressure. Our results provide guidance for implementation of a strategic SCN resistance rotation plan to manage the widespread virulence on PI 88788 and sustain the future durability of SCN resistance genes.