TOXICITY OF FUNGAL ENDOPHYTE SECONDARY METABOLITES TO PLANT-PARASITICNEMATODES AND SOIL-BORNE PLANT-PATHOGENIC FUNGI

Fungi isolated from the cortical tissue of surface sterilized tomato r oots collected from field plots produced secondary metabolites in nutr ition broth that were highly toxic to Meloidogyne incognita. Especiall y strains of Fusarium oxysporum were highly active with 13 of 15 strai ns producing culture filtrates toxic to nematodes. The mechanism of ac tion of the toxic metabolites produced by the non-pathogenic F. oxyspo rum strain 162 with proven biological control of M. incognita in pot e xperiments was investigated. These metabolites reduced M. incognita mo bility within 10 min of exposure. After 60 min, 98% of juveniles were inactivated. Juveniles were initially inactivated within a few minutes of exposure, but with exposure of 5 h 50% of the juveniles were dead and 24 h exposure resulted in 100% mortality. In a bioassay with lettu ce seedlings metabolite concentrations >100 mg/l reduced the number of M. incognita juveniles on the roots comparing to the water control. T he F. oxysporum toxins were highly effective towards sedentary parasit es and less effective towards migratory endoparasites. Non-parasitic n ematodes were not influenced at all. Metabolites of strain 162 also re duced significantly the growth of Phytophthora cactorum, Pythium ultim um and Rhizoctonia solani in vitro. Secondary metabolites of endophyti c fungi on plant-parasitic nematodes and soil-borne fungi should be co nsidered for control of plant parasitic nematodes and plant pathogenic fungi. The results also show the need for proper selection of target nematodes in in vitro bioassays.