Tam, V: Modes of action of non-pathogenic Fusarium oxysporum

Recently, mutualistic endophytic F. oxysporum isolates were documented as candidates for biological control against plant parasitic nematodes. However, understanding their mechanisms of action toward R. similis was poorly known. The following can be summarized from the present findings: 1. Pathogenicity of endophytic F. oxysporum isolates toward R. similis Non-pathogenic endophytic F. oxysporum isolates directly affected R. similis survival in the absence of banana plants. In both synthetic media and in the soil, F. oxysporum isolates decreased mobility of R. similis when compare to the untreated controls. F. oxysporum was not shown to be a parasite of the nematode. Toxins in culture filtrates of F. oxysporum isolates Fo162 and V5W2 reduced mobility of R. similis in vitro; however the toxic effects were not lethal. 2. Colonization, plant growth promotion and vegetative compatibility of endophytic F.oxysporum The F. oxysporum isolates Fo162 and V5W2 not only colonized excellently on banana roots a short time after fungal application but also persisted in the root tissues for over 14 weeks. The F. oxysporum isolates also promoted banana growth in long term experiments in the absence of R. similis. The F. oxysporum isolates A1, Fo162 and V5W2 were shown to be unrelated genetically tothe important pathogenic Fusarium wilt diseases of bananas and tomatoes by VCG testing. Therefore, these mutualistic endophytic F. oxysporum isolates are not only beneficial and non-pathogenic on bananas but also are not pathogenic to other crops. These results indicate that endophytic F. oxysporum isolates A1, Fo162 and V5W2 are strong candidates for biocontrol in the field. 3. Modes of action of non-pathogenic endophytic F. oxysporum isolates toward burrowing nematode R. similis on banana The F. oxysporum isolates reduced nematode penetration in banana plants when compared to untreated controls. The F. oxysporum not only reduced R. similis penetration, but also reduced nematode