Enzyme Production and Nitrogen Fixation by Free, Immobilized and Coimmobilized Inoculants of Trichoderma harzianum and Azospirillum brasilense and Their Possible Role in Growth Promotion of Tomato 

Momein H. El-Katatny*

Department of Botany and Microbiology, Faculty of Science, Minia University, P.O. Box 61519, El-Minia, Egypt

Article history:
Received July 1, 2009
Accepted December 20, 2009

Key words:
coimmobilization, alginate, Trichoderma harzianum, Azospirillum brasilense, enzyme production, nitrogen fixation, plant growth promotion, tomato growth, pot experiment

Summary:
A plant growth-promoting rhizobacterium (Azospirillum brasilense strain Az) and a biocontrol fungus (Trichoderma harzianum strain T24) have been evaluated for their individual and combined production of hydrolytic enzymes, nitrogen fixation and their possible role in growth promotion of tomato seedlings. The studied organisms were inoculated as free or calcium alginate-encapsulated cells. All freshly prepared macrobeads showed high encapsulation capacity (EC/%) of inocula compared with dry macrobeads. Results of enzyme production did not exhibit consistent pattern of the effect of encapsulation process on enzyme production. Beads entrapping bacterial and/or fungal cells were used successfully in 3 repeated cycles in the presence of fresh sterile culture medium in each growth cycle. Enzyme production by immobilized bacterial and/or fungal cells increased as the growth cycles were repeated. Co-culturing of A. brasilense with T. harzianum (free or immobilized) in semisolid nitrogen deficient medium (N-free medium) enabled A. brasilense to fix nitrogen on pectin, chitin and carboxymethyl cellulose. The activity of nitrogen fixation by A. brasilense in the case of single and combined cultures with Trichoderma (using dry encapsulated beads) into the sterile soil increased with the addition of carbon source. Most of inoculations with free or alginate macrobead formulations of T. harzianum and/or A. brasilense showed significant increase in the growth parameters of tomato seedlings. The root system grew more profusely in the case of all seeds treated with A. brasilense. The growth parameters of Az/T24-treated seeds using dry coimmobilized macrobeads were higher than those of the untreated control. Moreover, the effect was improved significantly in soil enriched with different C sources. Enhanced tomato seedling growth after the co-inoculation could be due to the synergistic effect of both Trichoderma and Azospirillum. Finally, co-inoculation with Azospirillum and other microorganisms is one of the major frontiers of Azospirillum technology and perhaps the main area for future applications.

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