Cyst Nematode Populations Research Articles

Influence of Winter Annual Weed Removal Timings on Soybean Cyst Nematode Population Density and Plant Biomass

Soybean cyst nematode (SCN) is one of the most yield limiting pathogens in U.S. soybean production. Henbit and purple deadnettle are winter annual weeds shown to facilitate SCN reproduction after crop harvest in the eastern Corn Belt. These weeds, along with volunteer soybean that germinates in autumn after harvest, are common to postharvest soybean production fields and provide an opportunity for SCN reproduction and population increase outside of the typical soybean production season. The objective of this experiment was to determine if autumn removal of these weeds and volunteer soybean can influence the winter weed seedbank, plant biomass, and SCN population densities. Microplots were established with or without Lamium spp. and volunteer soybean, and four winter weed removal timings (none, October, December, and May). Dry weights of autumn Lamium spp. were reduced 50% in October when grown in competition with volunteer soybean. SCN juveniles were found in henbit roots at higher densities in October (42 per gram of root) than December (5 per gram of root) and were also found in the roots of volunteer soybean (14 per gram of root) in October. SCN egg population densities were 50% lower in August after the summer fallow period. The results of this experiment suggest that autumn removal of winter annual weeds and volunteer soybean did not reduce SCN populations.

Molecular characterization of Canadian populations of potato cyst nematodes, Globodera rostochiensis and G. pallida using ribosomal nuclear RNA and cytochrome b genes

The mitochondrial cytochrome b gene (cytb), the internal transcribed spacer region (ITS1-5.8S-ITS2) of the rRNA gene and D2-D3 expansion segments of the 28S rRNA gene were amplified, sequenced and used to characterize several populations of potato cyst nematodes, Globodera pallida and G. rostochiensis, collected from different areas in Canada. Diagnostic PCR-ITS-RFLP profiles with three restriction enzymes are provided for identification of both species. Sequences of ITS rRNA and cytb genes were compared with those in Genbank of other potato cyst nematode populations originating from Europe, South America, USA, Australia and New Zealand. The ITS rRNA sequences of Canadian G. rostochiensis were similar to those of all previously sequenced populations of this species. Sequence divergence of ITS rRNA for G. rostochiensis varied from 0 to 1.6%, whereas for G. pallida sequence divergence among populations reached 1.95%. Sequence and phylogenetic analysis of cytb and ITS rRNA genes using Bayesian inference revealed that Canadian G. pallida is almost identical to European and USA populations and formed a large clade with all these populations on the phylogenetic trees. The present molecular result with cytb confirmed the hypothesis that there are possibly several sibling species within G. pallida. Our study also supports a previously proposed hypothesis regarding introduction of G. pallida from a restricted area in Peru, firstly into Europe with subsequent spread to other continents including North America. Our sequence analysis revealed that several newly obtained sequences cannot be translated into functional cytb protein, because point indels disrupt the reading frame. Poly(T) variation in mtDNA genes in G. pallida might be explained by post-transcriptional editing mechanisms in Globodera mitochondria as well as by errors during PCR amplification of mononucleotide repeats within these genes.

Esterase pattern in different populations of soybean cyst nematode.

This study aimed at comparing the phenotype for the isoenzym esterase in different populations of soybean cyst nematode (SCN) belonging to the types 1, 3, 6 and 14. Protein extracts from 1, 6 and 12 SCN females was run on a polyacrylamide gel electrophoresis at 8%. Esterase pattern was detected even from a single female. The esterase phenotype for this enzyme was similar in all the populations tested, and so this technique was unable to differentiate the esterase pattern.

Crop rotational and spatial determinants of variation inHeterodera avenae(cereal cyst nematode) population density at village scale in spring cereals grown at high altitude on the Tibetan Plateau, Qinghai, China

Cereal cyst nematode (Heterodera avenae) population densities were determined in spring cereals after harvest in three high-altitude villages in Qinghai, China in order to examine the effect of crop rotations. Two villages were sampled intensively to allow examination of between-field spatial variation. The previous season’s crop, including fields where two host crops had been grown in succession, did not appear to influence the final nematode density. A high degree of variation in population density and significant spatial variation appeared to be strongly influenced by the occurrence of hyperparasites, thus masking any possible crop rotation effects. Nevertheless, a third of the fields had final egg densities of greater than 10 eggs/g soil, creating a risk of yield loss if an intolerant host was to be grown in the next year. From the findings, it is suggested that future research should focus on developing locally adapted resistant cultivars and examining factors that determine the efficacy of natural biocontrol.

Superoxide dismutase isoelectric focusing patterns as a tool to differentiate pathotypes of Globodera spp.

Abstract Isoelectric focusing was used to separate proteins from cyst extracts of potato cyst nematode (PCN) populations. In a first set of assays, cyst extracts from standard populations of Globodera rostochiensis pathotypes Ro1, Ro2, Ro3, Ro2/3, Ro4, and Ro5, and G. pallida pathotypes Pa2 and Pa3, were loaded on isoelectric focusing gels. Gels were stained for superoxide dismutase (SOD), esterase, and glucose-6-phosphate isomerase (GPI). Twelve bands of SOD activity were detected, six (B1-B6) migrating towards the basic zone and the other six (A1-A6) migrating towards the acidic zone, starting from the loading point. A cluster analysis was carried out based on a data matrix that reported the presence or absence of SOD bands on the isozyme electrophoresis patterns (IEPs). Globodera spp. were clearly distinguished and, within G. rostochiensis, Ro2 and Ro4 shared a high level of similarity, respectively, with Ro3 and Ro5; moreover, Ro1 could be clearly distinguished from Ro2/3 and Ro4/5. Globodera pallida Pa2 and Pa3 also shared a high level of similarity. In contrast, esterase and GPI IEPs did not discriminate among G. rostochiensis standard pathotypes. Subsequently, 14 field populations of G. rostochiensis, five from Italy and nine from Venezuela, and three field populations of G. pallida, two from Italy and one from Chile, were assayed to obtain SOD IEPs. Italian populations had previously been identified at pathotype level by bioassays according to the generally accepted international test using different resistant potato cultivars and clones. The cluster analysis carried out on the SOD IEPs of all the populations tested formed four distinct groups within G. rostochiensis and only one within G. pallida. Pathotype identification of Globodera populations by SOD IEPs was not able to discriminate between bioassay standard couples Ro2/Ro3, Ro4/Ro5 and Pa2/Pa3. Therefore, three groups were assigned to Ro1, Ro2/3 and Ro4/5, and a fourth group to Pa2/Pa3. Four Venezuelan populations, not identified at pathotype level by bioassays, formed a distinct fifth group. By means of the method described herein, four additional unknown Venezuelan populations could be assigned to Ro1 group and one to Ro2/Ro3 group; one G. pallida population from Chile was assigned to Pa2/Pa3 group.

Oilseed Radish Effects on Soil Structure and Soil Water Relations

Oilseed radish (Raphanus sativus spp. oleifera) reduces sugarbeet cyst nematode (Heterodera schachtii) populations. Fall-incorporated radish biomass may also increase the yield and quality of subsequently grown sugarbeet (Beta vulgaris L.) by improving soil physical and hydraulic properties. This field study determined radish effects on nearsurface soil aggregate stability, water-stable aggregate size distribution, bulk density, and field-saturated water content, as well as infiltration and hydraulic conductivity measured at water supply potentials of -40, -20, and +0 mm H 2 O. In 2003 and 2004 in Twin Falls, ID, radish were grown in a Portneuf silt loam (Durinodic Xeric Haplocalcid) for about 10 weeks in the fall, then incorporated later that fall by disking, followed by moldboard plowing. In early May of the following year, sugarbeet were planted, irrigated, then harvested for yield and quality. In the spring and fall of each sugarbeet growing season, soil samples were collected from two depths, 0 to 5 and 5 to 50 mm, on which we measured aggregate stability and size distribution by wet sieving. Soil cores were collected from 0 to 34 mm to measure bulk density. Also in spring and fall, we used ponded and tension infiltrometers placed in the row to measure steadystate, unconfined infiltration rates and, from those rates, to

Morphological and molecular identification of potato cyst nematode populations in Serbia

Quarantine species such as potato cyst nematodes Globodera rostochiensis and G. pallida are present in Serbia since 1999 and 2005, respectively. These nematodes are sibling species and their morphological identification is complex due to their morphometric overlap. The cysts from the localities of Kladnica, Sanac, Gojna Gora and Milatovici were grown on susceptible potato varieties and their morphological differences have been discussed. To avoid ambiguities in species morphological designation a duplex PCR method was chosen for a rapid and accurate species identification. The whole procedure, from DNA extraction to DNA isolation, can be performed in a single day. .

Iso-lines and inbred-lines confirmed loci that underlie resistance from cultivar ‘Hartwig’ to three soybean cyst nematode populations

Soybean [Glycine max (L.) Merr.] cultivars varied in their resistance to different populations of the soybean cyst nematode (SCN), Heterodera glycines, called HG Types. The rhg1 locus on linkage group G was necessary for resistance to all HG types. However, the loci for resistance to H. glycines HG Type 1.3- (race 14) and HG Type 1.2.5- (race 2) of the soybean cyst nematode have varied in their reported locations. The aims were to compare the inheritance of resistance to three nematode HG Types in a population segregating for resistance to SCN and to identify the underlying quantitative trait loci (QTL). 'Hartwig', a soybean cultivar resistant to most SCN HG Types, was crossed with the susceptible cultivar 'Flyer'. A total of 92 F5-derived recombinant inbred lines (RILs; or inbred lines) and 144 molecular markers were used for map development. The rhg1 associated QTL found in earlier studies were confirmed and shown to underlie resistance to all three HG Types in RILs (Satt309; HG Type 0, P = 0.0001 R (2) = 22%; Satt275; HG Type 1.3, P = 0.001, R (2) = 14%) and near isogeneic lines (NILs; or iso-lines; Satt309; HG Type 1.2.5-, P = 0.001 R (2) = 24%). A new QTL underlying resistance to HG Type 1.2.5- was detected on LG D2 (Satt574; P = 0.001, R (2) = 11%) among 14 RILs resistant to the other HG types. The locus was confirmed in a small NIL population consisting of 60 plants of ten genotypes (P = 0.04). This QTL (cqSCN-005) is located in an interval previously associated with resistance to both SDS leaf scorch from 'Pyramid' and 'Ripley' (cqSDS-001) and SCN HG Type 1.3- from Hartwig and Pyramid. The QTL detected will allow marker assisted selection for multigenic resistance to complex nematode populations in combination with sudden death syndrome resistance (SDS) and other agronomic traits.

Variabilidade genética em populações de campo do nematóide de cisto da soja provenientes dos estados do Paraná e Rio Grande do Sul

ABSTRACT Genetic variability in field populations of the soybean cyst nematode from the states of Parana and Rio Grande do Sul, Brazil This work aimed to study the genetic variability in populations of the soybean cyst nematode (SCN), Heterodera glycines, using polycystic and monocystic populations for inoculation on differential hosts. Cysts of H. glycines were extracted from soil samples collected in soybean plantations from the counties of Cruz Alta RS and Porto Mendes PR and from Novo Horizonte PR, district of Marechal Cândido Rondon, with further inoculation of eggs and J2 on differential hosts. The differential host reaction, using polycystic inoculum, allowed only the identification of the prevalent race or the race with highest population within each sample. In the sample of Cruz Alta only race 3 was detected and in the sample of Porto Mendes only race 6. However, it was not possible to identify the prevalent race of H. glycines in the sample of Novo Horizonte. Nevertheless, when the genetic variability of SCN was studied within each population, using inoculum from populations built up from single cysts, races 6 and 3 were detected in the sample of Cruz Alta, races 6, 5 and 2 from Porto Mendes and races 10 and 6 from Novo Horizonte. Therefore, the monocystic process allowed to know the race diversity in the samples studied.

Short- and long-term tillage effects on Heterodera glycines reproduction in soybean monoculture in west Tennessee

Soybean cyst nematode, Heterodera glycines has been documented as the pathogen most consistently causing yield loss in US soybean production fields almost since its discovery in the US. No-tillage has been adopted in much of the soybean production areas to preserve soil and nutrients. The impact of this production practice change on soybean cyst nematode has been evaluated since the introduction of the practice over thirty years ago and mixed results on the impact have been recorded. This study was initiated to determine if tillage practices and timing of changes impacted soybean cyst nematode reproduction. The study was imposed on a long-term tillage study and treatments were changed to measure short-term as well as long-term effects of tillage on soybean cyst nematode. Significant differences in soybean cyst nematode population density were found between treatments. However, significant differences found could be attributed to short-term changes in tilled and no-tilled treatments. Soybean cyst nematode reproduction was almost twice as high in treatments which changed from no-tillage to disc than tilled treatments changed to no-tillage. No significant differences were found in yield among the treatments. Grain yield was reflective of cultivar grown and environmental conditions.

Analysis of Cyst and Cone Top Morphometrics of Indian Populations of Maize Cyst Nematode

Analysis of Cyst and Cone Top Morphometrics of Indian Populations of Maize Cyst NematodeHierarchical cluster analysis based on cyst and cone top morphometric means including cyst length, cyst width, cyst length to cyst width ratio, vulval slit length, vulval bridge length, vulval bridge breadth, under bridge breadth, length of fenestra, breadth of fenestra, distance from anus to fenestra and number of secondary bullae was used to learn more about cyst and cone top morphometric means and their relationships for six populations ofHeterodera zeaefrom Indore, Ludhiana, Delhi, Udaipur, Kanpur and Samastipur by using SPSS 13 for Windows computer software (SPSS Inc.). Values of proximity matrix based on cluster analysis of morphometrics and the dendrograms visually illustrated the grouping and relationships among populations. Intra specific variations in the different characters of the cone top structure revealed that Indore and Samastipur populations ofH. zeaewere different as compared to other ones ofH. zeae.Cluster analysis of cyst morphometrics showed that the populations ofH. zeaefrom Kanpur and Delhi were different as compare to other four ones.

Interactions between the potato cyst nematodes, Globodera pallida, G. rostochiensis, and soil-borne fungus, Rhizoctonia solani (AG3), diseases of potatoes in the glasshouse and the field

Abstract This is the first report of a positive interaction between the nematode Globodera pallida and Rhizoctonia solani diseases of potato, and is an important step in the general understanding of interactions between nematodes and fungal diseases. One glasshouse and two field experiments were performed to investigate interactions between G. pallida or G. rostochiensis and R. solani diseases of potatoes. The glasshouse experiment investigated the independent and combined effects of G. pallida or G. rostochiensis and R. solani on the growth of plants and R. solani disease severity. In the glasshouse experiment the combined effects of G. pallida with R. solani or G. rostochiensis with R. solani showed greater R. solani diseases of potatoes compared with only R. solani. The field experiments examined the development of R. solani diseases on potatoes grown in soil with potato cyst nematode population densities ranging from eight to 140 and four to 50 eggs (g soil)–1 in the years 2006 and 2007, respectively. The 2006 field experiment revealed a clear positive relationship between initial population densities of G. pallida and the incidence of stolons infected by R. solani, subsequent stolon pruning and stem canker. In both field experiments a clear positive relationship was found between densities of nematodes within the potato roots and the incidence of infected stolons, stolon pruning and stem canker. Nematicide applied together with R. solani in the 2007 field experiment reduced the effect of G. pallida on the incidence and severity of diseases caused by R. solani.

Morphological and Molecular Characterisation of Potato Cyst Nematode Populations from Tunisia and Survey of Their Probable Geographical Origin

Morphological and Molecular Characterisation of Potato Cyst Nematode Populations from Tunisia and Survey of Their Probable Geographical Origin

Effect of sample size on cyst recovery by flotation methods: Recommendations for sample processing during EU monitoring of potato cyst nematodes (Globodera spp.)

Under EC Council Directive 2007/33/EC member states of the European Union are recommended to take soil samples ranging from 100 mL to >1500 mL to monitor populations of potato cyst nematodes [PCN] (Globodera spp.) in targeted fields. This study examines the effects of varying sample size on sample processing and cyst extraction using two widely used laboratory methods. Cyst recovery was stable using the Fenwick can from 100 mL up to the physical limits of the can. Recovery was significantly lower for low density 50 mL samples; however, this was partly due to a statistical artefact since higher numbers of cysts were lost from successively larger samples with constant cyst numbers (i.e. decreasing densities). The Schuiling centrifuge had functional limits of <100 mL and >500 mL. Outside this range, cyst recovery from low density samples was significantly reduced. Cyst recovery from samples of varying size, but with equal numbers of cysts was only constant above 100 mL. However, samples ranging from 200–500 mL were optimal for the Schuiling centrifuge. Cyst extraction efficiency was similar using both methods for samples ranging from 150 mL to 1500 mL, where larger samples were divided into <500 mL portions. However, processing times (i.e. cyst extraction and microscopic examination) and water consumption increased significantly with increasing sample size and were significantly higher when using the Fenwick can.

Origin and genetic diversity of Western European populations of the potato cyst nematode (Globodera pallida) inferred from mitochondrial sequences and microsatellite loci

Native to South America, the potato cyst nematode Globodera pallida is one of the principal pests of Andean potato crops and is also an important global pest following its introduction to Europe, Africa, North America, Asia and Oceania. Building on earlier work showing a clear south to north phylogeographic pattern in Peruvian populations, we have been able to identify the origin of Western European populations with high accuracy. They are all derived from a single restricted area in the extreme south of Peru, located between the north shore of the Lake Titicaca and Cusco. Only four cytochrome b haplotypes are found in Western Europe, one of them being also found in some populations of this area of southern Peru. The allelic richness at seven microsatellite loci observed in the Western European populations, although only one-third of that observed in this part of southern Peru, is comparable to the allelic richness observed in the northern region of Peru. This result could be explained by the fact that most of the genetic variability observed at the scale of a field or even of a region is already observed at the scale of a single plant within a field. Thus, even introduction via a single infected potato plant could result in the relatively high genetic variability observed in Western Europe. This finding has important consequences for the control of this pest and the development of quarantine measures.

Effect of rotation crops on hatch, viability and development of Heterodera glycines

AbstractRotation with non-host crops can be an effective method for reducing soybean cyst nematode (Heterodera glycines) populations in soybean cropping systems. Sunn hemp, Illinois bundleflower, oilseed rape, perennial ryegrass, red clover, corn and H. glycines-susceptible soybean were compared for their effects on H. glycines hatch, viability and development in laboratory and glasshouse experiments. In the laboratory experiments, root exudates in soil leachates, extracts from fresh plant tissues, and extracts from residues of sunn hemp, red clover and soybean stimulated hatch of second-stage juveniles (J2) of H. glycines. All crops appeared to contain hatch inhibitors as well. There was no apparent effect of the root exudates and extracts from any of the crops on egg viability in vitro. When the H. glycines J2 were exposed to root exudates and extracts for 72 h, only the extracts of fresh plants and plant residue from sunn hemp, red clover and soybean, and the extract of plant residue from oilseed rape reduced viability of J2. In glasshouse experiments, residues of all crops, except Illinois bundleflower, reduced egg population density, with sunn hemp providing the greatest reduction. Residues of sunn hemp, red clover, and perennial ryegrass added to soil reduced the reproduction factor, suggesting the residues not only reduced egg population density but also reduced nematode infectivity. While all crops allowed penetration by J2, minimal development (to third- or fourth-stage juveniles only) occurred only in sunn hemp, red clover, oilseed rape and Illinois bundleflower, and full development occurred only in soybean. The results suggest that sunn hemp and red clover were the most effective rotation crops for managing H. glycines, and that stimulating hatch of H. glycines J2 was the main mechanism involved in reducing the H. glycines population density.

Variability in Distribution and Virulence Phenotypes of Heterodera glycines in Missouri During 2005.

The soybean cyst nematode, Heterodera glycines, is a serious economic threat to soybean producers in Missouri. Periodic monitoring for the presence, population densities, and virulence phenotypes of H. glycines is essential for determining crop losses and devising management strategies implementing the use of resistant cultivars. A survey using area-frame sampling was conducted to determine the distribution and virulence phenotypes of H. glycines in Missouri during 2005. Two samples from each of 125 fields representing eight geographical regions of Missouri were collected; 243 samples were processed for extraction of cysts and eggs. In all, 49% of samples had detectable cyst nematode populations, which ranged from 138 to 85,250 eggs per 250 cm3 of soil. Race and H. glycines type tests were conducted on populations from 45 samples. Nearly 80% of the populations that were tested, irrespective of the region, were virulent on the indicator line plant introduction (PI) 88788, which is the source of resistance for most H. glycines-resistant cultivars. More than 70% of populations could reproduce on the indicator lines PI 88788, PI 209332, and PI 548316 (Cloud), indicating that soybean cultivars with resistance derived from these sources need to be carefully monitored and used only in rotation with nonhost crops and soybean cultivars with resistance from other sources. Approximately one-third of the populations, primarily in the southern regions of Missouri, could reproduce on PI 548402 (Peking), another common source of resistance. Fewer than 10% of the populations could reproduce on PI 90763, PI 437654, PI 89772, or PI 438489B, suggesting that these sources of resistance should be used in soybean breeding programs to develop H. glycines-resistant soybean cultivars.

Laser capture microdissection (LCM) and comparative microarray expression analysis of syncytial cells isolated from incompatible and compatible soybean (Glycine max) roots infected by the soybean cyst nematode (Heterodera glycines)

Syncytial cells in soybean (Glycine max cultivar [cv.] Peking) roots infected by incompatible and compatible populations of soybean cyst nematode (SCN [Heterodera glycines]) were collected using laser capture microdissection (LCM). Gene transcript abundance was assayed using Affymetrix soybean GeneChips, each containing 37,744 probe sets. Our analyses identified differentially expressed genes in syncytial cells that are not differentially expressed in the whole root analyses. Therefore, our results show that the mass of transcriptional activity occurring in the whole root is obscuring identification of transcriptional events occurring within syncytial cells. In syncytial cells from incompatible roots at three dpi, genes encoding lipoxygenase (LOX), heat shock protein (HSP) 70, superoxidase dismutase (SOD) were elevated almost tenfold or more, while genes encoding several transcription factors and DNA binding proteins were also elevated, albeit at lower levels. In syncytial cells formed during the compatible interaction at three dpi, genes encoding prohibitin, the epsilon chain of ATP synthase, allene oxide cyclase and annexin were more abundant. By 8 days, several genes of unknown function and genes encoding a germin-like protein, peroxidase, LOX, GAPDH, 3-deoxy-D-arabino-heptolosonate 7-phosphate synthase, ATP synthase and a thioesterase were abundantly expressed. These observations suggest that gene expression is different in syncytial cells as compared to whole roots infected with nematodes. Our observations also show that gene expression is different between syncytial cells that were isolated from incompatible and compatible roots and that gene expression is changing over the course of syncytial cell development as it matures into a functional feeding site.

A time-course comparative microarray analysis of an incompatible and compatible response by Glycine max (soybean) to Heterodera glycines (soybean cyst nematode) infection

The development of an infection in soybean [Glycine max L. cultivar (cv.) Peking] roots by incompatible (I) and compatible (C) populations of soybean cyst nematode (SCN) (Heterodera glycines) was assayed using an AffymetriX soybean GeneChip. This time-course microarray analysis, using 37,744 probe sets, measured transcript abundance during I and C. These analyses reveal that infection by individual I and C H. glycines populations influence the transcription of G. max genes differently. A substantial difference in gene expression is present between I and C at 12 h post infection. Thus, G. max can differentiate between I and C nematode populations even before they have begun to select their feeding sites. The microarray analysis identified genes induced earlier in infection during I than C. MA also identified amplitude differences in transcript abundance between I and C reactions. Some of the probe sets measuring increased transcript levels during I represented no apical meristem (NAM) and WRKY transcription factors as well as NBS-LRR kinases. Later during I, heat shock protein (HSPs) probe sets (i.e. HSP90, HSP70, ClpB/HSP101) measured increased transcript abundance. These results demonstrate that G. max roots respond very differently to the different H. glycines races even before their feeding site selection has occurred. The ability of G. max to engage an I reaction, thus, appears to be dependent on the ability of root cells to recognize the different races of H. glycines because these experiments were conducted in the identical G. max genetic background.

Testing of potato varieties to assess resistance to Globodera rostochiensis and Globodera pallida

Testing of potato varieties to assess resistance to <i>Globodera rostochiensis</i> and <i>Globodera pallida</i>