University of Tasmania
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Isolation and characterization of some bacteria antagonistic to plant pathogenic fungi

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posted on 2023-05-27, 16:38 authored by Oedjijono,
Bacteria antagonistic to plant pathogenic fungi were isolated from various sources and tested for their ability to inhibit fungi or protect plants in vitro, in the glasshouse and in a field trial. Five strains of bacterial antagonists were isolated from daisy roots (Bacillus polymyxa UTl), decomposing woodchips (B. subtilis UT2), clary sage roots (Pseudomonas cepacia UT3 and P. putida UT4) and from white clover roots (Acinetobacter sp. UT5). In vitro, the degree of inhibition of fungi by the five antagonists varied, with strain UT3 showing antagonism to all fungal pathogens (Sclerotinia sclerotiorum; S. minor; Botrytis cinerea; Pythium ultimum; Fusarium solani; Phytophthora cinnamomi; P. cactorum; Gaeumannomyces graminis; and Penicillium echinulatum) tested. The action of the antagonists depended on the media used. Isolates of UTl and UT3 were inhibitory to the fungi on both PDA and KBM; the other strains were only inhibitory on PDA. Antifungal compounds produced by the antagonists were thought to be responsible for inhibiting the pathogens rather than ferric-siderophores, as addition of iron to the media did not affect the inhibitory activity of the antagonists. The antagonists (strains UTl, UT2, UJ\3 UT4 and NIR-6 of P. putida) significantly reduced wheat take-all disease in an axenic sand assay with isolate UT3 (P. cepacia) showing the most inhibition to the pathogen. The antagonists maintained their viability and ability to protect the wheat roots after 3 weeks of the assay. In the glasshouse the five antagonists (strains UTl to UT5) reduced lettuce (La.ctuca sativa) drop caused by either Sclerotinia sclerotiorum or S. minor compared with their controls after 10 weeks growth. In the field however the antagonists did not significantly protect daisy (Olearia phlogopappa) plants from the root rot disease caused by Pythium sp.. Metabolites produced by strains UTl and UT3 were inhibitory to several fungi in vitro. Strain UT3 of P. cepacia produced two types of antibiotic designated A and B. Compound A (the main inhibitor) was inhibitory to both fungi and bacteria tested while compound B (the minor inhibitor) was only inhibitory to the bacteria. The main compound had an Rp 0.40 and the minor had an Rp 0.87 on silica gel following development in a chloroform-methanol (7:3) solvent system. Both had very similar retention times (between 20 and 22 minutes) following separation by C1g reversed phase HPLC and elution with 0- 100% methanol containing 0.1 % trifluoroacetic acid. Both antibiotics were thermostable and resistant to acidic and alkaline treatments. Proton NMR indicated that the compound A may be an aromatic molecule but further characterization was not possible due to incomplete purification."


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Copyright 1992 the Author - The University is continuing to endeavour to trace the copyright owner(s) and in the meantime this item has been reproduced here in good faith. We would be pleased to hear from the copyright owner(s). Includes bibliographical references (leaves 137-169). Thesis (M.Sc.)--University of Tasmania, 1993

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