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Corn+Soybean Digest

Small Spore Stops SCN

Soybean cyst nematode (SCN) has been billed as the No.1 soybean pest. It steals yields by latching on to soybean roots. Some day soon there could be a new sheriff in town to stop the bushel thief. The sheriff's name is Pasteuria nishizawae, a bacterium that infects nematodes and can reduce SCN populations. Pasteuria is one of those happy accidental discoveries that occur when researchers go searching for answers to an illogical experiment result.

Greg Noel, USDA nematologist at the University of Illinois, set out to figure out why there were reduced numbers of SCN in his 16 ft.x16 ft. greenhouse screening beds. The beds were used to screen soybean germplasm to different SCN races, but egg counts got so low they were having trouble conducting experiments. Since decreasing numbers of SCN are uncommon, Noel tried to find the answer and discovered Pasteuria.

“I looked at some nematodes one day in the lab and found spores attached to them. I knew right away it was Pasteuria, but I didn't know which one,” says Noel. “It turned out to be P. nishizawae, the same Pasteuria found in Japan.”

He's not sure how the Pasteuria got to the U.S., but once it's in an SCN-infected field it starts killing nematodes. The Pasteuria infects juvenile nematodes and causes damage before the SCN has a chance to reproduce, which slows or stops SCN population growth in a field.

A Florida company has been working on getting the bacterium to the field. Pasteuria Bioscience, LLC, formed in May 2003, is trying to grow the bacterium in large enough quantities to apply in a field.

The company focused on Pasteuria penetrans, a bacterium that attacks root-knot nematode. Its research with P. penetrans should translate well in work with the SCN Pasteuria, P. nishizawae, when its patented process is perfected, the company says.

Thomas Hewlett, senior research scientist at Pasteuria Bioscience, says they're working on producing enough spores to field test P. penetrans — hopefully by next year. After that, it should take 2-3 years before the product is available to growers.

“It does work, guaranteed. We've used it at Disney's Epcot theme park,” Hewlett says. “The exhibit ‘The Land’ had root-knot nematode so bad that nothing would grow for more than a month. No pesticides can be used there. We applied P. penetrans and now they have control of root-knot nematode.”

Nematodes are very difficult to kill, but Hewlett says, “We're hopeful that we'll fast track through the EPA registration process. There isn't anything out there to back up the loss of methyl bromide and other nematicides that have recently been pulled off the market. Pasteuria is an effective, safe alternative.”

With Pasteuria, researchers have demonstrated that the biggest problems sometimes have the smallest solutions. It's a matter of time before SCN will be the prey, and not the predator, in U.S. soybean fields.

How Bacteria Kills A Nematode

“The nematode population increases while the Pasteuria population lags behind,” says Greg Noel, nematologist at the University of Illinois “Pasteuria then catches up, reducing the nematode population. With fewer nematodes to feed on the Pasteuria, population drops. It cycles over time.”

Noel says this classic predator/prey model means Pasteuria won't eliminate SCN from a field completely and it can take several years to reduce the population. However, Pasteuria should keep SCN from increasing unchecked. And that, in turn, should keep damage levels under control.

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