Heterodera glycines 

 

Contents

 

Rev 12/27/2013

Soybean Cyst Nematode Classification Hosts
Morphology and Anatomy Life Cycle
Return to Heterodera Menu Economic Importance Damage
Distribution Management
Return to Heteroderidae Menu Feeding  References
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Classification:

      Rhabditida
       Tylenchina
        Tylenchoidea
         Heteroderidae
          Heteroderinae
       Heterodera glycines

      Soybean Cyst Nematode

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Morphology and Anatomy:

 

Cysts on soybean rootlet.

Photograph by Charles Overstreet

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Distribution:

 Japan, China, Korea, Indonesia, South America, Soviet Union, Canada.

Distribution in US

Very widespread in the United States (in 26 states, including North Carolina, Texas, Oklahoma; limited distribution in Arkansas; approximately 1/3 of soybean fields in North Carolina are infested).

Slide #2 H. glycines is the most widespread cyst nematode in the United States.  It was first reported in the United States in North Carolina in 1954, but was reported in Japan in the 1880s as a race of H. schachtii.  Soybean cyst nematode is believed to have come to the U.S. from Japan with soil imported during the late 1800's to obtain nitrogen-fixing bacteria. SCN was first found in the U.S. in 1954 in North Carolina and rapidly moved to the Midwest. SCN is now present in all the major soybean growing states in the Midwest.

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Economic Importance:

A-rated pests in California.

During 2006-2009, soybean cyst nematode resulted in annual crop losses of US$1 billion annually in the US alone, making it the most imprortant pest of soybean (Koenning and Wrather, 2010; Liu et al., 2012)

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Feeding:

Feeding site establishment and development typical of
 genus.

.Slide #10
Nematodes induce multinucleate syncytial feeding sites in the host root.  Nematode damage stunts roots, reduces water uptake, interferes with nodulation by nitrogen-fixing bacteria, and reduces yield. 

As they feed, the nematodes grow and molt three times, becoming larger with each molt. Mature males move out of the roots to find females, but the females remain attached to the root and continue to feed. Once the males leave the root they will not reenter the root or feed again. 

Since nematodes in the Heteroderidae become sedentary from the late second stage onwards (except for the metamorphosis to males), the feeding site in the plant must be maintained in a condition favorable for perhaps five or six weeks to allow the nematode to fulfill its reproductive potential.  In H. glycines, the Hg30C02 effector protein of Heterodera glycines may be involved in active suppression of host defenses (Hamamouch et al., 2012). As of 2013, some 70 proteins have been discovered in nematode secretions; many are new or unknown (Thomas Baum, pers. com.).

 

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Hosts:

Soybean

For an extensive list of host plant species and their susceptibility, copy the name

Heterodera glycines

select Nemabase and paste the name in the Genus and species box

 

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Life Cycle:

Development and basic biology are similar to those of other cyst-nematodes.

Cysts on soybean root (approx. 0.5mm diam.)

Life cycle is 25 days at 23 C.

Males are present and mating occurs.

 

Slide #8
Slide #9 Emergence of second-stage juveniles from eggs is enhanced by root leachates. The juveniles are the motile and infective stage.
Slide #11

Male nematodes attracted to posterior region of female.

 

As the female matures her body swells and ruptures the root. She will mate with one or more males and begin producing eggs. Some eggs, 50 to 100, are produced outside of the female in an egg mass, but the majority of the eggs produced, 150 to 300, stay within the body of the female. The body cuticle "tans" after death of the female resulting in a brown, lemon-shaped cyst.

 

Four races have been reported (Golden, 1970); there may be a fifth race (or possibly up to 20 depending on host-range differentials that are used - see Riggs).

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Damage:

Causes "yellow dwarf" disease in soybeans.  Reduced yields.

Slide #5 Slide #4
Symptoms may be visible: stunted, yellow plants, resulting in poor canopy closure. These symptoms are most visible on light sandy soils where moisture stress is common or on heavier soils in years when rainfall and soil moisture are low. On heavier soils, you may only see these symptoms when SCN population densities are extremely high or not at all.  Distinctive symptoms may not be visible, but considerable yield loss is sustained. When soil moisture is optimum and soil fertility is high, there may be no obvious above ground symptoms.
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Management:

Detection:

Slide #4 The first step in SCN management is detecting the nematode and assessing population densities. 

Fall sampling is often most convenient and will give the producer more time to make management decisions.

Regulatory:  Rejection of infested plant material; federal quarantine was in effect in US from 1957 to 1972. 

Resistant Cultivars: Hartwig (USDA soybean breeder) produced many resistant soybean varieties.  The nematode is sexually reproducing and there appears to be considerable genotypic variability in field populations.  Repeated use of  resistant cultivars has led to selection of aggressive strains in many fields.  Current recommendations are to rotate susceptible and resistant varieties with non-host crops to have a stabilizing selection effect on the nematode. 

For a list of plant species or cultivars (if any) reported to be immune or to have some level of resistance to this nematode species, copy the name

Heterodera glycines

select Nemabase Resistance Search and paste the name in the Genus and species box

According to an Associated Press release in 2000, Midland Genetics Group, an alliance of six companies in Illinois, Iowa and Kansas, is the first to capitalize on a soybean plant first bred by Purdue University researchers that has proven resistant to more than 150 types of cyst nematode. Other companies are working to incorporate the new technology, called CystX, into their brands..

Much recent research was centered on the Hartwig soybean variety, which successfully resisted all versions of the nematodes but did not produce high yields. In 1994, Purdue University researchers finally bred the resistant capabilities of Hartwig into a higher-yield soybean variety. They spent two years testing it against every type of nematode they could before selling bought licensing rights to CystX.

In 2011 and 2012, resesarchers at Southern Illinois University Carbondale and the University of Missouri at Columbia identified and validated the gene at the Rhg4 (for resistance to Heterodera glycines 4) locus, a major driver in a soybean plant’s resistance to soybean cyst nematode. Soybean plants with multiple copies of a multi-gene block known as Rhg1 also show better resistance to soybean cyst nematode.  Both projects allow researchers to focus on these gene structures -- Rhg1 and Rhg4 -- to help them develop soybean cyst nematode resistant soybean varieties.

 The Rhg4  locus is a major quantitative trait locus contributing to resistance to H. glycines. Mutation analysis, gene silencing and transgenic complementation confirm that the gene confers resistance. The Rhg4 gene encodes a serine hydroxymethyltransferase (SHMT), an enzyme that is common in nature and found in both animal and plant kingdoms. The enzyme catalyzes conversions between serine and glycine and is essential for cellular carbon metabolism. Alleles of Rhg4 conferring resistance or susceptibility differ by two genetic polymorphisms that alter a key regulatory property of the enzyme. Soybean plants from a normally resistant variety, but with a mutated form of the SHMT gene, lost resistance to nematodes. When the SHMT gene was shut down by gene-silencing techniques, the normally resistant soybeans became susceptible. Transfer of the resistant form of the SHMT gene into normally susceptible soybeans conferred resistance to the nematode  (Liu et al., 2012).

 

In general, resistance in soybeans is expressed as a hypersensitive response.  Syncytia are initiated in both resistant and susceptible cultivars but degenerate in the resistant cultivars.  They become necrotic and unable to support nematode development (Huang, 1998).

 

Crop rotation:  Rotation to non-host crops for 2 years is very effective (up to 90% reduction in population). 

Slide #5 Planting non-host crops, such as corn, wheat, alfalfa, red clover,  reduces SCN population densities and provides other benefits. SCN has host plants other than soybeans, including dry beans and peas. Avoid planting these alternate host crops in SCN infested fields as population densities will increase.
SCN-resistant varieties have been developed from several plant introductions with unique resistance to specific populations or races of nematodes. The most common SCN race in the Midwest is race 3 and all resistant varieties are resistant to race 3. It is important to monitor SCN population densities in fields planted with SCN-resistant varieties. If population density increases when a resistant variety is planted, another source of resistance should be used next time. Slide #7

Nematicides Fumigants are more effective than non-fumigants

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References:

H.W. Kirby, J. Faghihi, G. Tylka, D. Jardine, G. Bird, W. Stienstra, P. Donald, T. Powers, B.D. Nelson, R. Mac Reidel, M.A. Draper, C. Grau. 2000.  SCN Coalition. http://www.exnet.iastate.edu/Pages/plantpath/tylka/coalition/coalinfo.html.  

Hamamouch, N., Li, C., Hewezi, T., Baum, T.J., Mitchum, M.G., Hussey, R.S., Vodkin, L.O., Davis, E.L. 2012.  The interaction of the novel Hg30C02 cyst nematode effector protein with a plant b-1,3-endoglucanase may suppress host defence to promote parasitism.  Journal of Experimental Botany.

Huang, J.S. 1998.  Mechanisms of resistance. Pp353-368 in Sharma, S.B. (ed). The Cyst Nematodes. Kluwer, Dordrecht.

Koenning, S.R., Wrather, J.A. 2010. Suppression of soybean yield potential in the continental United States from plant diseases estimated from 2006 to 2009. Plant Health Prog. http://dx.doi.org/10.1094/PHP-2010-1122-01-RS (2010).

Liu, S., Kandoth, P.K., Warren, S.D., Yeckel, G., Heinz, R.,Alden, J., Yang, C., Jamai, A., El-Mellouki, T.,. Juvale, P.S., Hill, J., Baum, T.J., Cianzio, S., Whitham, S.A., Korkin, D., Mitchum, M.G.,Meksem, K. 2012. A soybean cyst nematode resistance gene points to a new mechanism of plant resistance to pathogens. Nature doi:10.1038/nature11651.

 

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Copyright 1999 by Howard Ferris.
Revised: December 27, 2013.