Beneficial bacteria, aided by a "cocktail" of potent natural compounds, may offer a way to biologically control soybean cyst nematodes and other crop-damaging roundworms. That's the implication of ongoing studies by scientists with the Agricultural Research Service (ARS) and the Donald Danforth Plant Science Center (DDPSC) in St. Louis, Mo.
Petri dish tests and live-plant experiments at the St. Louis research center showed that the bacteria—members of the genus Pseudomonas—caused the nematodes to stop moving and, in some cases, disintegrate.
Phenazines, hydrogen cyanide and phloroglucinols are among the Pseudomonas compounds being examined for their biocontrol activity against the nematodes. However, no single compound has emerged as the sole cause of the worms’ demise, notes plant geneticist Patricia Okubara, with the ARS Root Disease and Biological Control Research Unit in Pullman, Wash.
Her DDPSC co-investigator, Chris Taylor, isolated the Pseudomonads from the banks of the Missouri and Mississippi rivers, farms and dried botanical specimens. All told, his Pseudomonas collection totaled 63 strains. Of those, he chose 20 for their ability to infect and kill the soybean cyst nematode (Heterodera glycines), root-knot nematode (Meloidogyne incognita) and/or the nematode Caenorhabditis elegans. Washington State University nematologist Ekaterini Riga showed that four of the 20 strains were also active against M. chitwoodi or M. hapla nematodes.
The cyst nematode is a top target of the scientists’ bacteria-based approach because of the substantial losses its feeding causes to America's $27 billion soybean crop. Treating soil with pesticides, rotating crops and planting resistant varieties help keep the pest's numbers in check. But chemical control is costly, crop rotation isn't always economically feasible, and resistant varieties are eventually overcome by virulent new biotypes of the nematode. Pseudomonads could also be used against quarantine pests, including the potato cyst nematode, Globodera pallida, recently found in Idaho.
According to Okubara, novel controls are needed that can be used as part of an integrated approach, with potential benefits including improved environment health, longer-lasting crop resistance, and reduced production costs.
Another, longer-term approach is to engineer crop plants to produce the nematode-neutralizing compounds themselves, adds Okubara, who began collaborating with Taylor in 2007 under a three-year National Research Initiative grant.
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