Soybean cyst nematodes (SCN), which cause staggering losses for American soybean growers, could ultimately get eaten alive by a bacterium.

A USDA-ARS scientist has the biological weapon to destroy SCN; he just needs to find a way to reproduce it in large quantities.

The bacterium is pasteuria. Greg Noel, a USDA-ARS plant pathologist at the University of Illinois, is leading the research on this microorganism.

Pasteuria is an obligate parasite. That means it can grow and reproduce only inside soybean cyst nematodes, Noel explains. It was discovered in research plots at the University of Illinois, where SCN populations had been declining for several years.

"It has great potential as a biological control for soybean cyst nematodes - the most promising organism discovered thus far," he says. "But much work needs to be done before it will be available."

There's no doubt that it can do a job on SCN. Pasteuria endospores in the soil attach to SCN juveniles and penetrate their bodies soon after they invade the soybean root. The bacterium then proliferates and matures in the developing SCN females, which become filled with endospores. Those parasitized females normally don't produce eggs.

The bacterium life cycle is completed when endospores move into the soil as the diseased nematodes disintegrate.

"Our studies have demonstrated that pasteuria is capable of maintaining SCN populations at densities below the damage threshold, at least in field plots," says Noel.

A different species of pasteuria has been used in Africa on different nematodes with some success.

Noel says the bacterium he's working with may be a new species. He and co-workers are trying to specifically identify it by making morphological and DNA comparisons to other pasteuria species.

The major problem, says Noel, is that pasteuria can't be grown in an artificial medium. It needs nematodes in order to reproduce.

"Currently, the only way to grow the pasteuria is to produce infected SCN females on soybean roots in the greenhouse," Noel reports. "Developing an artificial growth medium will be an extremely difficult task."

One advantage of using pasteuria as an SCN control: there presumably is no buildup of resistance by SCN, as can happen with SCN-resistant soybeans.

Private industry has expressed some interest in developing pasteuria, Noel says.

"Ultimately, it could be applied as a seed treatment," he notes.