4/29/99

Contacts:
Thomas Baum, Plant Pathology, (515) 294-2398
Steve Hanson, Agronomy, (515) 294-2475
Brian Meyer, Agriculture Information, (515) 294-0706

HOW SOYBEAN CYST NEMATODE WORKS THE AIM OF ISU RESEARCHERS

AMES, Iowa -- An Iowa State University researcher is gaining a better understanding of how soybean cyst nematode damages soybean plants.

Soybean cyst nematode (SCN) is the leading soybean pathogen worldwide, causing millions of bushels in yield losses annually. SCN are microscopic worms that attack the roots of developing soybean plants. Susceptible plants can suffer significant yield losses. Infected plants may or may not show visible signs of damage. If the nematode population is very high, yellow, stunted plants can be seen.

"We want to understand how SCN is able to establish a feeding site in a susceptible soybean plant," said Thomas Baum, a nematologist in the Department of Plant Pathology. "With that information, we can work to develop new genes for SCN resistance."

Baum is part of a national research effort to discover new genes for resistance to SCN. The project is supported by the United Soybean Board, which funds research using checkoff dollars contributed by soybean growers.

"A focus of our research has been to identify SCN genes that control secretions that the nematode must use for successful parasitism of soybean," said Baum, who collaborates on the project with nematologists Eric Davis of North Carolina State University and Richard Hussey of the University of Georgia.

The scientists discovered how the nematode moves through root tissue after it enters the soybean root. They found that SCN has genes that produce cellulase, an enzyme that breaks down cell walls. Cellulase is secreted from the stylet, or feeding tube, of the nematode. The researchers' work, which was the first time that cellulase genes had been isolated in an animal, was published last year in the Proceedings of the National Academy of Sciences.

After the nematode finds a desirable location within the root, it secretes chemicals that alter normal plant cells, transforming them into a feeding site. With the plant as its food source, the nematode grows and produces hundreds of offspring.

Now that they have identified SCN cellulase genes, the scientists can find out where and when SCN use the enzymes to infect soybean roots.

"The ultimate goal is to produce SCN-resistant transgenic soybean plants that inhibit the activity of cellulase genes," Baum said. "If these enyzmes that play a key role in the SCN infection of soybeans can be neutralized, soybean growers would have a new way to control the nematode in the field."

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