- Rhabditida
Tylenchina
Tylenchoidea
Heteroderidae
Heteroderinae
Heterodera glycines
Soybean Cyst Nematode
 |
|
|
Cysts on soybean rootlet.
Photograph by Charles Overstreet |
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).
 |
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. |
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)
Feeding site establishment and development
typical of
genus.
. |
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).
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
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.
|
 |
 |
Emergence of second-stage juveniles from eggs is enhanced by root
leachates. The juveniles are the motile and infective stage. |
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).
Causes "yellow dwarf" disease in soybeans.
Reduced yields.
 |
 |
| 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. |
 |
Detection:
 |
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).
 |
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. |
 |
Nematicides:
Fumigants are more effective than
non-fumigants.
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.
Copyright © 1999 by Howard Ferris.
Revised:
November 19, 2012.
