• A.K. RAYMUNDO, E.P. MILITANTE, M.U. GARC University of the Philippines at Los Banos, College, Laguna



A  series of  laboratory  and nursery  experiments were  conducted  specifically  to determine  the  efficacy of 85 strains  of Bacillus  species  and  15  actinomycetes  against  six  fungal  pathogens  isolated  from  damped-off  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.  Preliminary test using the agar-plug technique revealed that 18 of the bacterial isolates could suppress  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.  Further  screening  using  the  agar-diffusion method  disclosed  that  10  isolates were  effective  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.  Application  of  the  three  most  promising  antagonistic  bacteria  as  seed  treatment  s howed  that  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 able  to antagonize  the effect of P. debaryanum  in  this particular experiment. Seed  germination  and  seedling  survival were  likewise  improved with  the  application  of  the  three  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 by  the antagonist when they were simultaneously grown in culture media. There must have been a competitive interaction between the two microorganisms.  Any  essential  requirement  of  microorganisms  can  serve  as  potentially  possible  basis  for competition. Another was antibiosis which is an inhibitory effect exerted by an organism upon another organism  through the production of antibiotic compounds. Moreover, several strains of bacteria are effective in lysing cell walls of pathogenic  fungi  under  laboratory  conditions.  Lysis  is  often  attributed  to  production  of  cell  wall  degrading enzymes like chitinase and gluconase that may hydrolyze major constituents of fungal cell walls.  




Research Paper