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Researchers find microscopic worms that attack Montana's wheat
February 05, 2007 -- By Carol Flaherty
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| MSU plant pathologist Alan Dyer and MSU graduate student Wendy Johnson. Photo by Carol Flaherty |
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Dave Wichman had a problem. The superintendent of the Montana Agricultural Experiment Station's Central Agricultural Research Center at Moccasin had poor yield and a seeming "failure to thrive" in a wheat field that had adequate nutrients, moisture and sunshine.
Suspecting plant pathogens, Wichman sent soil samples to Alan Dyer in Montana State University's Plant Sciences and Plant Pathology Department for diagnosis. After finding a nematode known to attack wheat roots, Dyer wondered how wide-spread the nematodes were in Montana. He suggested that investigating the nematode's distribution within the state could be graduate student Wendy Johnson's master's thesis work. With Dyer's help, she designed a study that involved taking soil samples from around Montana to see how common the root-lesion nematodes had become in the state.
Johnson dug into the problem, and enlisted MSU Extension agents in 17 counties to collect 148 soil samples from sites they thought were under-producing despite what appeared to be good crop management.
Of the suspect sites, Johnson's work showed that 41 percent had "Pratylenchus neglectus" root lesion nematodes, and 14 percent of the samples had Neglectus in excess of the level known to produce economic problems.
"Damage from root lesion nematodes in wheat results in stunting, premature yellowing of older leaves, reduced tillering and low kernel weight," Johnson said. "It's very difficult to distinguish the damage from that caused by nutrient deficiencies and drought."
It's no surprise the nematodes hadn't been identified as a problem in Montana before. They are microscopic "worms" that are practically transparent. Root lesion nematodes thrive where other nematodes don't. By invading plant roots and carrying on most of their lifecycle inside the root, they remain active when the absence of free soil moisture would limit most nematodes.
Looking at details about where Extension agents collected the samples, Johnson determined that Neglectus nematodes were more numerous when samples came from fields that had been previously cropped to winter wheat rather than spring wheat, and they were higher in no-till fields than in fully tilled fields.
There are no chemical control methods approved for use in small grain, Dyer said. And, since nematodes previously were not known to be causing damage at an economically important level in Montana, no wheat varieties have been bred to resist them. Despite that, tests conducted in Oregon this past summer show two of Montana's spring wheat varieties, Choteau and McNeal, have some tolerance to nematode infestations. In addition, winter wheat breeder Phil Bruchner is now adding nematode resistance to his breeding program.
"We have made initial crosses for moving resistance to root-lesion nematodes into varieties," Bruckner said.
With no current controls available, Dyer plans to develop management tools for Montana's growers. Until that time, he suggests growers with high nematode populations consider rotating to field peas, since peas are poor hosts for the worm.
The good news for Montana is that a second species of root lesion nematode known to attack wheat, "Pratylenchus thornei," was not found in Montana so far. Once Johnson had found Neglectus, she expected to find Thornei as well, since the two generally appear together. However, none were identified from the samples taken in 2006. Since Thornei is known to coexist in most fields that have Neglectus, Extension agents will help Johnson get another 150 samples from more suspect fields in 2007. The soil samples will be taken in early spring when the nematodes have not yet entered the roots of the newly planted wheat.
Soil testing for nematodes can be made at numerous private and university affiliated laboratories. Check the following websites for recommended labs:
http://www.bcc.orst.edu/bpp/Nematodes/contact.htm
or
http://www.cdfa.ca.gov/phpps/ppd/NematologySHProtocol.htm
Alan Dyer (406) 994-6535 or adyer@montana.edu or Wendy Johnson at wendy.lewis@myportal.montana.edu
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