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SUMMARYThe potential of cyanobacteria-based compost formulations was evaluated in cotton crop at two agroecological locations (Nagpur and Sirsa) as plant growth promoting (PGP) and biocontrol agents. Compostbased formulations fortified with Calothrix sp. or Anabaena sp. enhanced germination and fresh weight of plants, and microbiological activity by 10-15%, besides increased available nitrogen (by 20-50%) in soil at Nagpur. In the fungi-infected fields at Sirsa, Anabaena-T. viride biofilmed formulation performed the best, recording 11.1% lower plant mortality than commercial Trichoderma formulation. Scanning electron microscopy confirmed the colonisation of inoculated cyanobacteria/biofilms on roots. Significant correlation between mortality, increased activity of hydrolytic enzymes and fresh weight of plant roots were recorded. Calothrix sp. and Anabaena sp. proved promising as both PGP and biocontrol agents, while biofilmed formulations substantially reduced mortality of cotton plants in sick plots. This study illustrates the promise of cyanobacteria as viable inoculation option for integrated nutrient and pest management strategies of cotton.

Biofilms represent mixed communities present in a diverse range of environments; however, their utility as inoculants is less investigated. Our investigation was aimed towards in vitro development of biofilms using fungal mycelia (Trichoderma viride) as matrices and nitrogen-fixing and P-solubilizing bacteria as partners, as a prelude to their use as biofertilizers (biofilmed biofertilizers, BBs) and biocontrol agents for different crops. The most suitable media in terms of population counts, fresh mass and dry biomass for Trichoderma and Bacillus subtilis/Pseudomonas fluorescens was found to be Pikovskaya broth ± 1 % CaCO(3), while for Trichoderma and Azotobacter chroococcum, Jensen's medium was most optimal. The respective media were then used for optimization of the inoculation rate of the partners in terms of sequence of addition of partners, fresh/dry mass of biofilms and population counts of partners for efficient film formation. Microscopic observations revealed significant differences in the progress of growth of biofilms and dual cultures. In the biofilms, the bacteria were observed growing intermingled within the fungal mycelia mat. Further, biofilm formation was compared under static and shaking conditions and the fresh mass of biofilms was higher in the former. Such biofilms are being further characterized under in vitro conditions, before using them as inoculants with crops.

Bacteria-mediated plant growth promotion is a well-established and complex phenomenon that is often achieved by the activities of more than one plant growthpromoting (PGP) trait, which may not always be present in a single organism. Biofilms developed using a combination of two organisms with useful plant growth-promoting rhizobacteria (PGPR) traits may provide a definite advantage. In this context, in vitro studies were conducted evaluating the PGP traits of novel biofilms developed using Trichoderma as matrix and agriculturally important bacteria (Azotobacter chroococcum, Pseudomonas fluorescens and Bacillus subtilis) as partners. Such biofilms exhibited higher values for various biochemical attributes as compared to the individual organisms and dual cultures. Trichoderma-Bacillus and Trichoderma-Pseudomonas biofilms exhibited enhanced antifungal activity, ammonia, indole acetic acid (IAA) and siderophore production, as compared to the other treatments. Trichoderma-Azotobacter biofilm recorded the highest nitrogenase activity and 1-aminocyclopropane-1carboxylic (ACC) deaminase activity. The synergism in terms of the PGP traits in the biofilms revealed their promise as superior PGP inoculants.

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