Heterodera glycines

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.

Economic Importance:

Feeding:

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.

Hosts:

Life Cycle:

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).

Damage:


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.

Management:

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 their 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.

CHAMPAIGN, Illinois (AP) -- Researchers may have finally whipped the dreaded cyst nematode, a resilient pest that eats the roots of soybean plants and ruins more than $1 billion worth of crops across the country every year.

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, but Midland is first to test the technology and get it to market.

The cooperative's partners say they will start selling seed later this year for farmers to plant next spring. "They saw the material in the field very early and made a quick decision," said Rick Vierling, a geneticist at Purdue. "They were convinced this was something customers would want and they jumped on board. For a small company, it's a big deal, but then sometimes smaller companies can move faster."

Private and university researchers have worked for years to find some way to stop the cyst nematode, which chews up soybean roots and lowers yields. A typical farmer in cyst nematode regions can lose 5 percent of his soybeans, while a really bad infestation can wipe out almost an entire crop. "In our area there are a lot of other stresses involved, especially weather stresses, on growing soybeans," said Clyde Sylvester, an owner of one of the Midland companies in Ottawa, Kansas. "We felt like if we could keep the nematodes off the soybeans, it really makes them tougher against the other stresses."

Before now, scientists made progress with soybeans that fought off a few types of nematodes, but not all. Much of the latest research has centered on the Hartwig soybean variety, which successfully resisted all versions of the nematodes but didn't produce high enough yields to win over farmers. In 1994, Purdue 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. Midland, followed by other companies Purdue is not allowed to identify, bought licensing rights to CystX.

CystX was developed using a high-tech, but still natural breeding process, geneticist Rick Vierling said. So while technologically advanced, it's not a genetically modified organism, he said. Midland's owners put the bulk of their resources behind CystX, working at a harried pace to breed Purdue's variety with their own soybean types.

Midland project coordinator Dennis Brown said the resistance has proven itself time and again in Midland research stations in the United States and South America. "We were the first to really believe in it," said Brown, a farmer and seed dealer in Neoga, Illinois. "In southern Illinois, we've been dealing with this problem for 15 to 20 years, but we haven't been dealing with it quite well enough."

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.

Heterodera glycines	Contents	Rev 05/16/2006
Soybean Cyst Nematode	Classification	Hosts
	Morphology and Anatomy	Life Cycle
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