Rhizobacteria are known to influence plant by direct and indirect
mechanisms. Some strains of bacteria namely, Azotobacter chroococcum, Pseudomonas fluorescens, Paenibacillus polymyxa, Bacillus megaterium var phosphaticum, B. subtilis, B. coagulans, and Azospirillum lipoferum were screened for their beneficial mechanisms
to use them as plant growth-promoting rhizobacteria and biological control agents against two important soil-borne root infecting plant pathogens, i.e. Fusarium oxysporum f. sp lycopersici and F. solani. The obtained data revealed that, B. megaterium and P. polymyxa were more potent for phosphate solubilization while A. chroococcum, P. polymyxa and A. lipoferum were the most strains to grow on N-free media. All strains were able to produce indole-3- acetic acid (IAA) with higher production in the presence of tryptophan especially B. megaterium, P. polymyxa, A. chroococcum and A. lipoferum.
On the other hand, Ps. fluorescens, P. polymyxa and B. subtilis are more potent to produce catechol-type siderophores, chitinase, cellulase and protease and they were more efficient for inhibition of fungal growth, either by using dual culture technique or by using filtrates of their respective cultures. Culture filtrates of Ps. fluorescens, P. polymyxa and B. subtilis were slightly exhibited antagonism against some bacterial strains used in the current study. By using 10 antibiotics to test the sensitivity for antibiotics, A. chroococcum and B. coagulans were the most sensitive bacteria to all the tested antibiotics, while Ps. fluorescens and P. polymyxa were the most resistant.
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Key words: rhizobacteria, mycolytic enzymes, siderophores, antagonism, biocontrol agents |
