THE EFFECT OF FUNGAL APPLICATION RATE AND NEMATODE DENSITY ON THE EFFECTIVENESS OF VERTICILLIUM-CHLAMYDOSPORIUM AS A BIOLOGICAL-CONTROL AGENT FOR MELOIDOGYNE-INCOGNITA

Five application rates of Verticillium chlamydosporium (0, 50, 500, 5000 and 50,000 chlamydospores/g soil) and five inoculum densities of Meloidogyne incognita (0, 50, 500, 5,000 and 25,000 juveniles/plant) were tested in a factorial experiment on tomato plants grown in pots. The effects of nematode and fungal inoculum density on fungal colonisation of soil and tomato roots, as well as nematode control and invasion of the roots were studied. Even when roots were extensively colonised by V. chlamydosporium, invasion of the roots by juveniles was not affected by the fungus. Establishment of V. chlamydosporium in soil was dependent on the initial fungal inoculum rate used. Increase in numbers of colony forming units in soil were greater from a small initial inoculum than from a large one. This suggests that V. chlamydosporium depends partly on external nutrients in soil for its establishment. Colonisation of the rhizoplane depended on initial fungal inoculum and on galling caused by M. incognita; higher fungal and nematode inoculum levels resulted in greater colonisation of the roots. Although galled roots were most extensively colonised by V. chlamydosporium, the fungus was least effective in controlling M. incognita at high nematode densities, presumably because many egg-masses stayed embedded in the gall tissue and were therefore protected from fungal attack.