Submitted to: Journal of Nematology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: March 4, 1999
Publication Date: N/A
Interpretive Summary: Billions of dollars worth of crop damage are caused each year in the United States by plant-parasitic nematodes, a type of microscopic worm. These nematodes are difficult to control with synthetic chemical pesticides because the nematodes live below ground and attack plant roots. Also, many synthetic pesticides currently used for control of plant-feeding nematodes are being phased out due to hazards to the environment and to animal and human health. A potentially safer and effective alternative is the use of microorganisms that produce natural nematicides. However, only a small fraction of microorganism species is useful for this purpose and identifying beneficial strains can be extremely time consuming. To address this problem, we developed techniques to evaluate high numbers of fungus strains in the laboratory for production of compounds reducing nematode egg hatch and viability of juvenile worms. Methods were developed for two nematodes species: a root-knot nematode that attacks a wide variety of crops and the soybean cyst nematode which is a major pest of soybeans. Using these methods, we found that a strain of the fungus Fusarium equiseti secreted compounds that inhibited root-knot nematode egg hatch and immobilized juvenile nematodes after hatch. The results are significant because they provide a quick method of screening fungi for nematode antagonism. This research will be used by scientists discovering new microorganisms capable of managing plant-feeding nematodes in an environmentally sound manner.
In vitro methods were developed to test fungi for secretion of metabolites affecting nematode egg hatch and mobility of second-stage juveniles. Separate assays were developed for two nematodes: root-knot nematode (Meloidogyne incognita) and soybean cyst nematode (Heterodera glycines). Sodium hypochlorite was more effective than chlorhexidine diacetate or formaldehyde solutions at surface-disinfesting soybean cyst nematodes eggs from greenhouse cultures. Subsequent rinsing with sodium thiosulfate to remove residual chlorine from disinfested eggs did not improve either soybean cyst nematode hatch or juvenile mobility. Soybean cyst nematode hatch in all culture media was lower than in water. Sodium hypochlorite was also used to surface-disinfest root-knot nematode eggs. In contrast to soybean cyst nematode, root-knot nematode hatch was higher in potato dextrose broth medium than in water. Using the in vitro methods reported here, the broth of the fungus Fusarium equiseti was found to inhibit root-knot nematode egg hatch and was investigated in more detail. Broth extract and its chemical fractions not only inhibited egg hatch but also immobilized second-stage juveniles that did hatch, confirming that the fungus secretes nematode-antagonistic metabolites and that the procedures detected such metabolites.