Radopholus similis is one of the key pests of banana in the East African Highlands and in the world. Although control of this pest has mainly relied on the use of clean planting material, re-infestation of plants in the field remains a critical concern. Alternative management options such as the use of fungal endophytes may be used to provide protection and extend plant life. In this study, a total of 35 endophytic Fusarium isolates were screened for the production of secondary metabolites antagonistic to R. similis in culture. Undiluted and diluted culture filtrates were tested against motile stages of R. similis and eggs. Tests were conducted using culture filtrates of the fungal isolates grown in banana corm broth. All isolates tested demonstrated some level of in vitro antagonistic activity on the mobility of R. similis mixed stages (males, females and juveniles). The percentage of immobilized nematodes increased with increase in the length of exposure time to culture filtrates. After 24 hrs exposure, up to 100% of nematodes were immobilized compared to 26.5% in control treatments. Mortality of mixed stages of R. similis exposed to culture filtrates for 24 hrs, followed by rinsing with sterile distilled water, demonstrated that the effects of culture filtrate treatment were irreversible, as nematodes did not recover and were considered dead. Nematode mortality rates after 24-hr exposure periods ranged from 76.4% to 100.0%. The effects of culture filtrates on R. similis motile stages increased with increasing culture filtrate concentration. Culture filtrates also demonstrated inhibitory effects on hatching of R. similis eggs. Radopholus similis males were more sensitive to culture filtrate treatment than females. The results obtained demonstrate the potential for using endophytic Fusarium isolates as biological control agents against R. similis and/or toxic derivatives as potential nematicides against the nematode.
Thesis (PhD (Plant Pathology))--University of Pretoria, 2006.