Soybean Cyst Nematode Cysts Research Articles

Evaluation of Compost and Manure Amendments for Suppressing Heterodera glycines.

Soybean cyst nematode (SCN) is a major pest of soybean crops, causing significant yield losses and economic impact. Current management strategies primarily rely on resistant varieties, cover crops, and seed treatments. In addition, there is a growing interest in developing sustainable, ecologically based approaches to integrate SCN risk reduction into soybean production systems. This study aimed to evaluate the efficacy of various compost and manure amendments in suppressing SCN populations and promoting soybean productivity. An in vitro egg hatching assay was conducted to screen the inhibitory effects of different compost and manure extracts on SCN egg hatching. Results indicated that poultry manure, Layer Ash Blend, and swine manure extracts significantly inhibited SCN hatching compared with other treatments across multiple time points. Greenhouse trials further validated the effectiveness of Layer Manure, poultry manure, High Carbon Dairy Doo, and Seed Starter 101 in suppressing SCN cysts, eggs, and juveniles. A field microplot trial confirmed the potential of Layer Ash Blend and poultry manure in SCN management, with significant reductions in SCN populations and increased soybean yields. The study also investigated the impact of these amendments on promoting the population of bacterivorous and frugivorous nematodes, contributing to a biological diverse soil ecosystem. Overall, the results indicate that amending SCN-infested soil with specific compost or manure formulations can effectively suppress nematode populations while improving soybean productivity. These findings contribute to the development of sustainable strategies for SCN management in soybean production systems.

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.

Robotic agricultural instrument for automated extraction of nematode cysts and eggs from soil to improve integrated pest management

Soybeans are an important crop for global food security. Every year, soybean yields are reduced by numerous soybean diseases, particularly the soybean cyst nematode (SCN). It is difficult to visually identify the presence of SCN in the field, let alone its population densities or numbers, as there are no obvious aboveground disease symptoms. The only definitive way to assess SCN population densities is to directly extract the SCN cysts from soil and then extract the eggs from cysts and count them. Extraction is typically conducted in commercial soil analysis laboratories and university plant diagnostic clinics and involves repeated steps of sieving, washing, collecting, grinding, and cleaning. Here we present a robotic instrument to reproduce and automate the functions of the conventional methods to extract nematode cysts from soil and subsequently extract eggs from the recovered nematode cysts. We incorporated mechanisms to actuate the stage system, manipulate positions of individual sieves using the gripper, recover cysts and cyst-sized objects from soil suspended in water, and grind the cysts to release their eggs. All system functions are controlled and operated by a touchscreen interface software. The performance of the robotic instrument is evaluated using soil samples infested with SCN from two farms at different locations and results were comparable to the conventional technique. Our new technology brings the benefits of automation to SCN soil diagnostics, a step towards long-term integrated pest management of this serious soybean pest.

Coinfection of soybean plants with Phytophthora sojae and soybean cyst nematode does not alter the efficacy of resistance genes

AbstractThe soybean cyst nematode (SCN) Heterodera glycines and the oomycete Phytophthora sojae are among the most damaging pathogens of soybean worldwide. Resistant cultivars are commonly used to manage these diseases. As it is known that the presence of SCN can facilitate the development of other pathogens, it is important to verify if there is a synergistic activity between SCN and P. sojae. The purpose of this study was to evaluate a possible interaction on susceptible and resistant soybean lines. The plants were inoculated with one or both organisms at different stages (5 or 10 days old). Two levels of SCN inoculum (2,000 and 10,000 eggs/plant) and different timing between SCN and P. sojae inoculation (2, 5, or 8 days) were compared. The results on 5‐day‐old plants showed that SCN did not influence P. sojae development. The resistant cultivar to P. sojae remained effective (0% mortality) and susceptible cultivars exhibited high mortality (100%) in the presence or absence of SCN. Experiments on 10‐day‐old plants showed that SCN resistance was not affected by the presence of P. sojae. SCN inoculum density and timing of P. sojae infection did not affect the virulence of these pathogens and the efficacy of resistance genes. However, the number of SCN cysts was decreased by more than 50% (p < .001) when P. sojae was coinfesting the susceptible cultivar. This suggests that P. sojae might indirectly influence SCN development by reducing the root mass. This study confirmed that resistant cultivars remain a valid option for the management of P. sojae and SCN.

Seasonal Variation and Crop Sequences Shape the Structure of Bacterial Communities in Cysts of Soybean Cyst Nematode.

Soybean cyst nematode (SCN), Heterodera glycines Ichinohe, is the number 1 pathogen of the important economic crop soybean. Bacteria represent potential biocontrol agents of the SCN, but few studies have characterized the dynamics of bacterial communities associated with cysts under different crop rotation sequences. The bacterial communities in SCN cysts in a long-term soybean–corn crop rotation experiment were investigated over 2 years. The crop sequences included long-term soybean monoculture (Ss), years 1–5 of soybean following 5 years corn (S1–S5), years 1 and 2 of corn following 5 years soybean (C1 and C2), and soybean–corn annual rotation (Sa and Ca). The bacterial 16S rRNA V4 region was amplified from DNA isolated from SCN cysts collected in spring at planting, midseason (2 months later), and fall at harvest and sequenced on the Illumina MiSeq platform. The SCN cyst microbiome was dominated by Proteobacteria followed by Actinobacteria, Bacteroidetes, and Verrucomicrobia. The bacterial community composition was influenced by both crop sequence and season. Although differences by crop sequence were not significant in the spring of each year, bacterial communities in cysts from annual rotation (Sa and Ca) or crop sequences of early years of monoculture following a 5-year rotation of the alternate crop (S1 and C1) became rapidly differentiated by crop over a single growing season. In the fall, genera of cyst bacteria associated with soybean crop sequences included Rhizobacter, Leptothrix, Cytophaga, Chitinophaga, Niastella, Streptomyces, and Halangium. The discovery of diverse bacterial taxa in SCN cysts and their dynamics across crop rotation sequences provides invaluable information for future development of biological control of the SCN.

Assessment of Insecticide/Miticide Treatments on Soybean Cyst Nematode Bioassays Under Greenhouse Conditions

The soybean cyst nematode (SCN)–soybean pathosystem is often reproduced under greenhouse conditions for basic research purposes, increasing inoculum, and soybean germplasm screening. Application of pesticides for SCN bioassays is often necessary for keeping insect and mite pest populations under control. The research presented here looks at the application of several foliar pesticides (active ingredients; abamectin, bifenthrin, clofentezine, imidacloprid, kinoprene, and pyridaben), a soil-applied imidacloprid, and combinations of pesticides on bioassays to determine if pesticide applications have a negative impact on SCN female and cyst numbers as well as egg and second-stage juvenile (J2) production, which could lead to dubious results. Results from this experiment demonstrate these chemicals can be used to control pest populations on soybean without significantly altering SCN female, cyst, egg, and J2 counts.

Mycobiome of Cysts of the Soybean Cyst Nematode Under Long Term Crop Rotation.

The soybean cyst nematode (SCN), Heterodera glycines Ichinohe (Phylum Nematoda), is a major pathogen of soybean. It causes substantial yield losses worldwide and is difficult to control because the cyst protects the eggs which can remain viable for nearly a decade. Crop rotation with non-host crops and use of biocontrol organisms such as fungi and bacteria offer promising approaches, but remain hampered by lack of knowledge of the biology of nematode parasitic organisms. We used a high-throughput metabarcoding approach to characterize fungal communities associated with the SCN cyst, a microenvironment in soil that may harbor both nematode parasites and plant pathogens. SCN cysts were collected from a long-term crop rotation experiment in Southeastern Minnesota at three time points over two growing seasons to characterize diversity of fungi inhabiting cysts and to examine how crop rotation and seasonal variation affects fungal communities. A majority of fungi in cysts belonged to Ascomycota and Basidiomycota, but the presence of several early diverging fungal subphyla thought to be primarily plant and litter associated, including Mortierellomycotina and Glomeromycotina (e.g., arbuscular mycorrhizal fungi), suggests a possible role as nematode egg parasites. Species richness varied by both crop rotation and season and was higher in early years of crop rotation and in fall at the end of the growing season. Crop rotation and season also impacted fungal community composition and identified several classes of fungi, including Eurotiomycetes, Sordariomycetes, and Orbiliomycetes (e.g., nematode trapping fungi), with higher relative abundance in early soybean rotations. The relative abundance of several genera was correlated with increasing years of soybean. Fungal communities also varied by season and were most divergent at midseason. The percentage of OTUs assigned to Mortierellomycotina_cls_Incertae_sedis and Sordariomycetes increased at midseason, while Orbiliomycetes decreased at midseason, and Glomeromycetes increased in fall. Ecological guilds of fungi containing an animal-pathogen lifestyle, as well as potential egg-parasitic taxa previously isolated from parasitized SCN eggs, increased at midseason. The animal pathogen guilds included known (e.g., Pochonia chlamydosporia) and new candidate biocontrol organisms. This research advances knowledge of the ecology of nematophagous fungi in agroecosystems and their use as biocontrol agents of the SCN.

English

The soybean cyst nematode (SCN), Heterodera glycines, is present in more than 150 municipalities in Brazil, and the long persistence of the cysts in the soil combined with the severe degree of parasitism induces high soybean production losses. The objective of this study was to evaluate the biofumigant effect of Crambe abyssinica on the SCN population in the second soybean crop season. The experiment was conducted on a rural property whose soil was naturally infested with SCN. Crambe abyssinica was planted in the second crop season following harvest, and in the subsequent crop season, 4 soybean varieties, 2 resistant and 2 susceptible to SCN, were planted. The nematode population was evaluated every month for 90 days after planting. In the second crop season, when C. abyssinica was in the field, there was a significant decrease in the number of adult SCN females and cysts. During the 90-day period after C. abyssinica cultivation, when plant residues were incorporated into the soil and the area was planted with soybeans, both the number of adult SCN females / 10 g roots and the number of cysts decreased. This result indicates that C. abyssinica reduced the nematode population during its time in the field. Key words: Crambe, Glycine max, soybean nematode cyst, culture control.

Comparison of Two Soil Sampling Methods for Estimating Population Densities of Heterodera glycines Cysts

Soybean cyst nematode (SCN) is a significant economic pest of soybean in Ohio and the Midwest, in which yield losses are directly linked to the population density and distribution of cysts within a field. Advances in automation technology have been used to expedite soil fertility sampling for large-scale and high-density field maps. In this study, we explored the use of this technology as an option for sampling for SCN. There was a significant positive correlation for the number of SCN cysts between soil samples collected with an Automated Precision Soil Sampler and those collected using the traditional soil sampling method from three separate fields (P < 0.05, r values of 0.79 to 0.93). These results suggest that expedited soil sampling in fields with high population densities could be an added benefit for soybean farmers to encourage more sampling for SCN to monitor population levels as part of their overall management program. Accepted for publication 18 July 2016. Published 12 August 2016.

Influence of Two Herbicides on Soybean Cyst Nematode (Heterodera glycines) Reproduction on Henbit (Lamium amplexicaule) Roots

Soybean cyst nematode (SCN) is the most yield-limiting pathogen of soybean in the United States. Henbit is a prevalent winter annual weed species in no-till fields and is reported to be an alternative host of SCN. A greenhouse study was conducted to evaluate how the development of SCN on henbit roots was affected by herbicide mode of action and time of herbicide application. Henbit plants were grown in watertight pots placed in a water bath bench that kept soil temperature constant (27 ± 1 C) during the study. Ten d after transplanting, pots were inoculated with approximately 1,000 SCN eggs. At 7, 14, or 21 d after inoculation (DAI), henbit plants were sprayed with recommended dose of either glyphosate (870 g ae ha−1) or 2,4-D (1,070 g ae ha−1). The experiment was arranged in a randomized complete block design with five replications per treatment, and two experimental runs separated in time. At 28 DAI, the total number of SCN cysts and eggs, and plant shoot and root dry weight per pot were determined. Henbit root and shoot biomass increased as the time of herbicide application was delayed. Glyphosate reduced root biomass more than 2,4-D, but no differences in shoot biomass were detected. The number of SCN cysts per henbit plant and eggs per cyst increased as the herbicide application was delayed from 7 to 21 DAI. Glyphosate reduced the number of cysts found on henbit roots more than 2,4-D, especially at earlier application times. On plants treated with glyphosate, SCN-females produced only half the number of eggs of SCN-females on henbit plants treated with 2,4-D, regardless of time of application. These results indicate that early control of henbit plants, especially with glyphosate, can reduce SCN reproduction potential in SCN infested fields.

Plant Growth and Soybean Cyst Nematode Response to Purple Deadnettle (Lamium purpureum), Annual Ryegrass, and Soybean Combinations

A greenhouse study was conducted to determine the influence of soybean cyst nematode (SCN) –susceptible and –resistant plant combinations on SCN population densities and plant growth. Purple deadnettle, annual ryegrass, SCN-resistant and -susceptible soybean were planted in pots alone or in combination at one plant pot−1. Annual ryegrass and purple deadnettle reduced soybean growth. Pots with SCN-resistant plants had lower numbers of SCN cysts and eggs than pots with SCN-susceptible plants. However, an SCN-susceptible species grown with any of the SCN-resistant plants resulted in higher cyst counts than pots with only SCN-resistant plants. From an SCN management standpoint, this research suggests that there may be no incentive to using annual ryegrass as a cover crop over planting other SCN-resistant crops to reduce SCN population density.

Development of Soybean Cyst Nematode on Henbit (Lamium amplexicaule) and Purple Deadnettle (Lamium purpureum)

A survey of seven production fields in Indiana, Illinois, and Ohio was conducted to assess henbit and purple deadnettle growth and soybean cyst nematode (SCN) development and reproduction on these weeds. Autumn and spring growth of purple deadnettle and henbit was influenced by location within each state. In general, winter annual weeds were larger in size and reached maturity earlier in the spring at the southern sample sites than those in the north. All growth stages of SCN were found to be associated with henbit and purple deadnettle at both autumn and spring sample timings. SCN juveniles were generally found infecting roots at highest abundance in the spring. SCN cyst and egg production also were widespread and occurred to a much higher degree during the autumn than the spring developmental period. The results of this survey indicate that management tactics designed to minimize the potential for SCN reproduction on winter annual weeds would probably be most effective if conducted in the autumn, when the majority of SCN reproduction occurred. However, spring populations of winter annual weeds that harbor SCN juveniles might facilitate additional SCN reproduction and population increase if the weeds are not controlled in a timely manner prior to planting.

Purple Deadnettle (Lamium purpureum) and Soybean Cyst Nematode Response to Cold Temperature Regimes

An experiment was conducted in growth chambers to determine the influence of cold temperature regimes, designed to simulate winter temperature conditions and spring recovery, on the interaction between purple deadnettle and soybean cyst nematode (SCN). The study was a factorial arrangement of treatments with five levels of temperature (20, 15, 10, 5, or 0 C), two levels of exposure time to the temperature (10 or 20 d), and two levels of recovery time at 20 C following exposure (0 or 20 d). In general, purple deadnettle shoot and root growth increased with temperature and time. The ability of purple deadnettle to recover from cold temperatures declined as the length of time that the plant was subjected to the cold temperature increased. SCN juveniles per gram of root at the conclusion of the temperature treatment declined as the temperature increased from 0 to 15 C, likely a result of continued purple deadnettle root growth and the inhibition of SCN hatch, growth, or development at those temperatures. SCN female, cyst, and egg production per gram of root generally increased with temperature and occurred under all temperature regimes. The results of this research indicate that, after hatching, SCN juveniles can survive a period of cold temperature inside the roots of a winter annual and continue development when transferred to warmer temperatures. Therefore, in a field environment, where fall or spring alone may not be sufficient for SCN to complete a reproductive cycle on a winter annual weed, the nematode may be able to reproduce by combining the fall and spring developmental periods.

Influence of Intraspecific Henbit (Lamium amplexicaule) and Purple Deadnettle (Lamium purpureum) Competition on Soybean Cyst Nematode Reproduction

A greenhouse study was conducted to determine the effect of henbit and purple deadnettle density on weed biomass accumulation and soybean cyst nematode (SCN) reproduction. SCN did not impact shoot or root dry weight of purple deadnettle, henbit, or soybean. Foliar and root biomass of henbit and purple deadnettle were comparable but the biomass per stem was higher for purple deadnettle. Shoot and root biomass per pot of henbit and purple deadnettle at corresponding plant densities were statistically similar and were generally higher with increasing plant density. Henbit produced a greater number of stems than purple deadnettle and the least number of stems for both species existed at low densities. Purple deadnettle allowed for more SCN reproduction than did henbit. Weed densities also influenced SCN cyst and egg production but the results were species dependent. The highest SCN reproduction per pot was supported at low to moderate densities of purple deadnettle but at moderate to high densities of henbit. These results suggest that purple deadnettle should be more aggressively managed than henbit in management programs for SCN, but that henbit, especially at high densities, can support SCN reproduction at levels near those of purple deadnettle.

The Effect of rhg1 on Reproduction of Heterodera glycines in the Field and Greenhouse and Associated Effects on Agronomic Traits

The soybean cyst nematode (SCN) (Heterodera glycines Ichinohe) continues to be the most damaging soybean pest [Glycine max (L.) Merr.] in the USA. A major gene that provides partial resistance to SCN is rhg1, which is located on linkage group (LG) G. The objectives of this study were to test the effect of rhg1 on SCN reproduction in both the field and greenhouse and on agronomic traits in the field. Two populations of near isogenic lines (NILs) that segregated for rhg1 were developed to test the effect of the gene. These NIL populations were tested for their ability to support SCN cyst development in a thermo‐regulated water bath in a greenhouse and egg production estimated from soil samples taken from each plot in field tests. The NIL populations were evaluated for agronomic traits in field plots to determine the associated effects of rhg1 on these traits. In the greenhouse, NILs predicted to be carrying the resistance allele for rhg1 on the basis of a linked marker supported significantly (P < 0.01) fewer cysts than NILs carrying the susceptibility allele. In field tests, the final egg population density (Pf) was significantly lower and there was a smaller reproductive rate (Rf) in NILs carrying the resistance allele at rhg1 than susceptible NILs for both populations across and within environments in 2003. In only one population did the resistant NILs out‐yield the susceptible NILs, and this occurred only when the initial SCN pressure was high [>500 SCN eggs (100 cm3 soil)−1]. These results show that resistance at rhg1 can have a large effect on SCN reproduction and may result in a significant yield increase.

Bacteria associated with cysts of the soybean cyst nematode (Heterodera glycines).

The soybean cyst nematode (SCN), Heterodera glycines, causes economically significant damage to soybeans (Glycine max) in many parts of the world. The cysts of this nematode can remain quiescent in soils for many years as a reservoir of infection for future crops. To investigate bacterial communities associated with SCN cysts, cysts were obtained from eight SCN-infested farms in southern Ontario, Canada, and analyzed by culture-dependent and -independent means. Confocal laser scanning microscopy observations of cyst contents revealed a microbial flora located on the cyst exterior, within a polymer plug region and within the cyst. Microscopic counts using 5-(4,6-dichlorotriazine-2-yl)aminofluorescein staining and in situ hybridization (EUB 338) indicated that the cysts contained (2.6 +/- 0.5) x 10(5) bacteria (mean +/- standard deviation) with various cellular morphologies. Filamentous fungi were also observed. Live-dead staining indicated that the majority of cyst bacteria were viable. The probe Nile red also bound to the interior polymer, indicating that it is lipid rich in nature. Bacterial community profiles determined by denaturing gradient gel electrophoresis analysis were simple in composition. Bands shared by all eight samples included the actinobacterium genera Actinomadura and STREPTOMYCES: A collection of 290 bacteria were obtained by plating macerated surface-sterilized cysts onto nutrient broth yeast extract agar or on actinomycete medium. These were clustered into groups of siblings by repetitive extragenic palindromic PCR fingerprinting, and representative isolates were tentatively identified on the basis of 16S rRNA gene sequence. Thirty phylotypes were detected, with the collection dominated by Lysobacter and Variovorax spp. This study has revealed the cysts of this important plant pathogen to be rich in a variety of bacteria, some of which could presumably play a role in the ecology of SCN or have potential as biocontrol agents.

Irrigation of Soybean Cultivars Susceptible and Resistant to Soybean Cyst Nematode

Soybean cyst nematode (SCN) (Heterodera glycines Ichinohe) infests soils throughout the mid and lower Mississippi River Valley and the southeastern Coastal Plain in the USA, a region where irrigation is widely practiced. This study was conducted to determine the effect of irrigation on number of SCN cysts and seed yield of three soybean [Glycine max (L.) Merr.] cultivars that have varying levels of SCN resistance when grown in monoculture on SCN‐infested Dundee silt loam (fine‐silty, mixed, thermic, Aerie Ochraqualf) that has a perched water table. Cultivars (all Maturity Group V) were Forrest (resistant to SCN Race 3), A5474 (resistant to SCN Races 3 and 4), and Bay (susceptible to SCN). Bay was grown with and without nematicide applied after planting. Irrigation treatment was either with or without supplemental water during reproductive development of soybean. Neither seed yield nor number of SCN cysts at planting or harvest were significantly (P = 0.05) affected by irrigation on this soil. Application of nematicide to Bay plots reduced the number of SCN cysts at harvest, but did not significantly affect seed yield. Number of SCN cysts was lowest in A5474 plots, and seed yield of A5474 was highest in the second and third year of the study. Irrigation did not significantly interact with cultivar or nematicide to affect cyst number or seed yield. We conclude that irrigation during reproductive development of soybean did not affect (i) cultivar response to infection with SCN, (ii) the capability of SCN to maintain cysts on any cultivar, or (iii) the yield‐limiting effect of SCN on susceptible cultivars. This suggests that SCN effects on soybean are more complex than simply restricting water uptake by roots.

Soybean Cyst Nematode and Rhizobium Strain Influences on Soybean Nodulation and N2‐fixation1

AbstractThe spread of the soybean cyst nematode (SCN) (Heterodera glycines Ichinhoe) has required the breeding of resistant soybean [Glycine max (L.) Merr.] cultivars. The SCN causes a reduction in nodulation and N2‐fixation which may explain part of the yield reductions associated with SCN infestations. This study was designed to determine the interaction effects of SCN resistant and susceptible cultivars, Rhizobium japonicum (Kirch.) Buchanan strains, and SCN races on nodulation and N2‐fixation.The susceptible cultivar ‘Williams’ and resistant cultivars ‘Bedford’, ‘Forrest’, and ‘Franklin’ were grown on sterile sand culture in the greenhouse and inoculated with all possible combinations of SCN races 3 and 4 and R. japonicum strains 3, 110, and 123. Bedford and Forrest inoculated with strain 110 had the highest specific N2(C2H2)‐fixation activity (SA), but Bedford, Forrest, and Franklin inoculated with strain 123 had the largest nodule mass (NM). SCN race 3 did not reduce NM, but reduced both total N2(C2H2)‐fixation activity (TA) and SA. Race 4 did not influence TA and was inconsistent in its influence on SA and NM.Total N2(C2H2)‐fixation activity and SA was estimated at the R2 (determinate) and R4 (indeterminate) stages on several field‐grown soybean cultivars. The number of SCN cysts per 250 cc of soil (cyst index) also was determined. Resistant cultivars had low cyst indices and high N2‐fixation potentials. Susceptible cultivars had higher cyst indices and generally lower N2‐fixation rates but ‘Williams’, ‘Wayne’, and ‘York’ exhibited high fixation potentials despite high cyst indices. Nodule serology indicated a significant cultivar ✕ strain interaction which may account for the TA and SA differences.These results indicate that nodulation and N2‐fixation are influenced by cultivar ✕ Rhizobium strain and SCN race interactions and that the SCN is not equally deleterious to all susceptible cultivars. Williams and Wayne may be especially valuable in breeding resistant cultivars since they exhibited good nodulation and N2‐fixation despite high cyst indices.