Among 33 botanicals screened against Fusarium oxysporum f. sp. cubense (Foc), the causal agent of Fusarium wilt disease of banana, only the Zimmu leaf extract recorded 100% inhibition of both mycelial growth and spore germination of the Foc pathogen. Further evaluation of Zimmu leaf extract at different concentrations under greenhouse conditions in cv. Grand Naine (Cavendish-AAA) showed complete suppression of Fusarium wilt disease (disease score of 1.0 which means healthy) at 50 and 100% concentration in both application methods viz., drenching as well as dipping the banana roots in Zimmu leaf extract. Soil application of Zimmu leaf extract completely inhibited the germination of Foc propagules within 20 days of treatment under micro pot conditions. The field evaluation conducted in cv. Grand Naine (Cavendish -AAA) in Foc-sick field also demonstrated that drenching with Zimmu leaf extract (50% concentration w/v) recorded very low internal wilt disease scores of 1.5 when compared with control plants which recorded 5.8 on a disease scale of 1 to 6. In addition to significantly increasing plant growth parameters such as plant height, girth and number of leaves, the Zimmu leaf extract treatment also increased the yield parameters in particular bunch weight to 80.8% as compared to untreated control plants. The principle compound involved has been identified as a lipid. This is the first report on the suppressive effect of Zimmu leaf extract on banana Fusarium wilt disease and the finding of this study would ultimately be useful for the sustainable and farmer friendly management of the disease worldwide.
Key words: Fusarium wilt, banana, Fusarium oxysporum f.sp. cubense, Zimmu, plant extract.
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