BIOLOGICAL CONTROL OF DAMPING-OFF FUNGI OF AGOHO (CASUARINA EQUISETIFOLIA L.) USING ANTAGONISTIC BACTERIA
AbstractAÂ series ofÂ laboratoryÂ and nurseryÂ experiments wereÂ conductedÂ specificallyÂ to determineÂ theÂ efficacy of 85 strainsÂ of BacillusÂ speciesÂ andÂ 15Â actinomycetesÂ againstÂ sixÂ fungalÂ pathogensÂ isolatedÂ fromÂ damped-offÂ agoho. These damping-off fungi were: Fusarium oxysporum Schet., Rhizoctonia solani Kuhn., Phytophthora parasitica Dastur, Pythium debaryanum Hesse, and two unidentified pathogens temporarily designated as Unk 1 and Unk 2.Â Preliminary test using the agar-plug technique revealed that 18 of the bacterial isolates could suppressÂ two or more of the six damping-off fungi. Fusarium oxysporum was inhibited by 17 bacterial isolates, R. solani by 8 isolates, P. parasitica by 14 isolates and P. debaryanum by 15 isolates. The unidentified damping-off fungi Unk 1 and Unk 2 were inhibited by 13 and 9 isolates, respectively.Â FurtherÂ screeningÂ usingÂ theÂ agar-diffusion methodÂ disclosedÂ thatÂ 10Â isolates wereÂ effectiveÂ antagonists with Bacillus subtilis (Code No. R060), Bacillus sp. (Code No. R071), and Streptomyces sp. (Code No. R086) as the consistent and most effective inhibitors.Â ApplicationÂ ofÂ theÂ threeÂ mostÂ promisingÂ antagonisticÂ bacteriaÂ asÂ seedÂ treatmentÂ s howedÂ thatÂ they effectively inhibited the growth of the damping-off fungi in the laboratory as exhibited by an increase in percent germination. Bacillus subtilis however, was not ableÂ to antagonizeÂ the effect of P. debaryanumÂ inÂ this particular experiment. SeedÂ germinationÂ andÂ seedlingÂ survival wereÂ likewiseÂ improved withÂ theÂ applicationÂ ofÂ theÂ threeÂ most promising antagonistic bacteria as seed treatment. This was shown after three months under nursery conditions. There were possible mechanisms of control by the antagonistic bacteria against the damping-off fungi. The mycelium and spores of the pathogenic fungus may have been attacked and parasitized byÂ the antagonist when they were simultaneously grown in culture media. There must have been a competitive interaction between the two microorganisms.Â AnyÂ essentialÂ requirementÂ ofÂ microorganismsÂ canÂ serveÂ asÂ potentiallyÂ possibleÂ basisÂ for competition. Another was antibiosis which is an inhibitory effect exerted by an organism upon another organismÂ through the production of antibiotic compounds. Moreover, several strains of bacteria are effective in lysing cell walls of pathogenicÂ fungiÂ underÂ laboratoryÂ conditions.Â LysisÂ isÂ oftenÂ attributedÂ toÂ productionÂ ofÂ cellÂ wallÂ degrading enzymes like chitinase and gluconase that may hydrolyze major constituents of fungal cell walls. Â
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