Soybean Cyst Nematode
S. Sardanelli
Reviewed April 2010
Introduction
Due to its severe injury to host plant roots, rapid reproduction and persistence
in the soil, the soybean cyst nematode is considered a serious agricultural
pest. The life cycle of the soybean cyst nematode is completed in about one
month. It is possible to have three to six generations in a single cropping
year, depending upon location. Soybean cyst nematodes enter the root tissue
of susceptible plants and feed internally.
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Life Cycle
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| Drawing
of the life cycle of soybean cyst nematode, Heterodera glycines (McGawley) |
Painting
of the soybean cyst nematode, Heterodera glycines. (Cush) |
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| Second-stage
juveniles of soybean cyst nematode penetration the root of soybean (stained
red) (Eisenback) |
Infective
second-stage juveniles of soybean cyst nematode penetrating roots (stained
red) (Eisenback) |
Six
stages are involved in the life cycle of this nematode: an egg stage, four juvenile
(larval) stages, and the adult stage.
The second stage juvenile is the mobile and infective stage, worm-like in
appearance and unable to be seen with the naked eye. It penetrates the roots
and punctures the cells with a spear-like structure (stylet), then migrates
toward food-conducting tissues where it feeds.
Nematode feeding activities, alters the anatomy of the root system. As a
result, normal root function is disrupted and translocation of water and nutrients
is impaired.
The female can produce 50 to several hundred eggs, the majority of which
remain inside the female body. Others are deposited in a gelatinous mass in
the soil. After the female dies, the body remains intact and hardens into
a tough leathery sac known as a cyst. Eggs and juveniles can persist in these
cyst bodies for several years until they are stimulated to hatch in the presence
of host plants.
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| Soybean
cyst, Heterodera glycines, broken open to reveal numerous eggs contained
inside (McGawley) |
Eggs
of soybean cyst nematodes containing second-stage juveniles (McGawley) |
Female
soybean cyst nematodes, Heterodera glycines, compared to a nodule on the
root system (McGawley) |
As
in other species of Heterodera, physiological races or biotypes have been identified
for the soybean cyst nematode. These races differ in ability to develop on different
soybean varieties. Therefore, in any program of control or breeding for resistance,
the question of race must be considered.
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Recognizing the Presence of Soybean
Cyst Nematode
When poor plant growth is observed in a soybean
field, the possibility of soybean cyst nematode infestation should be considered:
Above
Ground Symptoms-
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| Soybean
field infested with soybean cyst nematode, Heterodera glycines (Eisenback) |
Closeup
of soybean stunted from infection by soybean cyst nematode, Heterodera
glycines (top) (Eisenback) |
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- Circular patches of plants which exhibit much poorer growth than the
surrounding areas
- Stunting, yellowing, wilting
- Significant reduction in yield
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Below Ground Symptoms-
Dig roots
and carefully remove excess soil. Any or all of the following may be observed:
- A shallow bushy root system
- Drastically reduced root system and root necrosis in heavily infected
plants
- Inhibition of rhizobium nodule formation on the roots
- A hand lens is usually required to detect the presence of cyst bodies
on the roots
- Cysts are approximately 1/4 to 1/2 the size of a pinhead
|
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| Soybean
cyst nematode, Heterodera glycines, on soybean (McGawley) |
|
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Sampling and Diagnosis
Should the presence of soybean cyst nematode be suspected, samples should
be taken. The Nematode Diagnostic Laboratory "Sampling Procedures" fact sheet outlines
the methods for accurate sampling. For scouting information, refer to
"Scouting
for Soybean Cyst Nematode"(an acrobat file requiring Adobe
Acrobat Reader), by the Iowa State University Extension service.
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Management of Soybean Cyst Nematode
The existence of the cyst, containing viable eggs and juveniles, is the single
most important factor which makes the soybean cyst nematode so difficult to
control. The tough cyst body, besides providing long-term protection for eggs
and juveniles, also provides the possibility of long distance dispersal. Cysts
are found in "soil-peds" (aggregates of soil) which adhere to anything
that moves through the infested field. Therefore, in order to restrict the
spread of soybean cyst nematodes to uninfested areas, and to control the populations
in known infested fields, the following management practices are necessary:
Sanitation measures
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| Cleaning
a tractor with compressed air to remove soil containing the soybean cyst
nematode, Heterodera glycines. |
|
- Farm machinery and clothing, especially footwear, should be cleaned before moving
from a known infested area to an uninfested site.
- The movement of contaminated materials, such as nursery plants, root
crops, and poorly cleaned seed, containers used in transport, from an infested
area, is a primary means of spread for soybean cyst nematode.
- Because this nematode has a number of weed species as hosts, weed control
is an aid in control of nematode population buildup.
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Crop rotation
- A nonhost crop should be planted for two (preferably three) years
between the planting of susceptible soybean crops
- The fact that rotation might not be economically acceptable to the
grower must be considered
- Any plan for the use of crop rotation as a control method must be
designed with the knowledge of the existing nematode population(s) in the
field and the specific crop to be grown.
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Resistant Varieties
- Soybean varieties with resistance to soybean cyst nematode have been developed
and are available to growers.
- These resistant varieties are not severely damaged by the nematode
and can reduce the population by literally starving the nematode.
- Resistant varieties will not eradicate the cysts but their use will
eliminate the necessity of lengthy rotations and allow the grower to produce
crops for which his agricultural operations were designed.
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| Resistant
and susceptible soybeans growing in a Heterodera glycines infested field
(J. P. Ross) |
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- Over-use of resistant varieties can lead to the emergence of new strains
or races of nematodes.
- Susceptible varieties should occasionally be used in rotational plans rather
than growing resistant varieties continuously.
- An alternative would be to use a resistant variety for one or two seasons
only and rotate with a nonhost crop when feasible.
- Extensive breeding programs are developing new varieties in the state.
- In Maryland the races most commonly detected have been races 1 and
3.
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Chemical Management
Chemical Management involves
the use of certain non-volatile nematicides, which are applied to the soil
to reduce nematode populations.
Recommendations may be found in current University of Maryland Extension
Service publications.
Nematode populations cannot be eradicated, but can only be reduced to economically
insignificant levels. The reduction of nematode numbers is accomplished through
use of the above-mentioned management tactics. The fact that cyst contents
may remain viable in fallow soil for years ranks this nematode among those
with the greatest longevity in the soil. However, with proper management and
utilization of specific control measures, successful soybean production can
continue in infested fields.
All pictures are courtesy of Nemapix Jounal of Nematological Images, vol.
1 &2, J.D. Eisenback & Ulrich Zunke, eds.
