In-vitro assays of Meloidogyne incognita and Heterodera glycines for detection of nematode-antagonistic fungal compounds

In-vitro methods were developed to test fungi for production of metabolites affecting nematode egg hatch and mobility of second-stage juveniles. Separ ate assays were developed for two nematodes: root-knot nematode (Meloidogyn e incognita) and soybean cyst nematode (Heterodera glycines). For egg hatch to be successfully assayed, eggs must first be surface-disinfested to avoi d the confounding effects of incidental microbial growth facilitated by the fungal culture medium. Sodium hypochlorite was more effective than chlorhe xidine diacetate or formaldehyde solutions at surface-disinfesting soybean cyst nematode eggs from greenhouse cultures. Subsequent rinsing with sodium thiosulfate to remove residual chlorine from disinfested eggs did not impr ove either soybean cyst nematode hatch or juvenile mobility. Soybean cyst n ematode hatch in all culture media was lower than in water. Sodium hypochlo rite was also used to surface-disinfest root-knot nematode eggs. In contras t to soybean cyst nematode hatch, root-knot nematode hatch was higher in po tato dextrose broth medium than in water. Broth of the Fungus Fusarium equi seti inhibited root-knot nematode egg hatch and was investigated in more de tail. Broth extract and its chemical fractions not only inhibited egg hatch but also immobilized second-stage juveniles that did hatch, confirming tha t the fungus secretes nematode-antagonistic metabolites.