03-08-2013, 04:16 PM
Biofilmed Formulations - A Novel Approach for Developing Effective Inoculants for Sustainable and Integrated Pest Management in Cotton
ABSTRACT
Microbial biofilms represent communities of microorganisms adhering to biotic /abiotic surfaces, which are embedded in an organic matrix of biological origin that provides structure and stability to the community. Competition for colonization sites and a continuous supply of nutrients through root exudates is an important factor determining the success of most interactions between plant, bacteria and pathogens in soil. In general, in most cases, the density of microbial community in the soil of such naturally occurring beneficial microorganisms is too low to prove consistent effects. The high population density achieved in biofilms provides the opportunity to perform biochemical reactions that single cells cannot accomplish efficiently; however, this strategy has not been explored for developing more robust inoculants in agriculture. Our investigation focussed towards the development of biofilms under in vitro conditions, using combinations of potent agriculturally important microorganisms (Bacillus subtilis, Pseudomonas fluorescens and Azotobacter chroococcum) with the fungus Trichoderma viride as the matrix. Such biofilms were evaluated as am environment-friendly option and their promise in reducing the severity of fungal diseases in cotton crop.
Optimization of protocols for biofilm development involved determining population load, sequence of addition of partners, media recipes and growth conditions. Observations revealed that the selected bacteria showed a synergistic relationship, with progressive and concomitant increase in population of both the partners, confirmed by microscopic imaging. Static conditions significantly improved biofilm development compared to shaking conditions, leading to significantly higher biomass. The biochemical traits of novel Trichoderma based biofilms revealed that biocontrol traits - ammonia, HCN and siderophore production were significantly enhanced, and were significantly correlated with antifungal activity against Macrophomina phaseolina, as compared to individual or dual cultures. Biofilms also exhibited enhancement in multiple PGP traits like nitrogen fixation, phosphorus solubilization, IAA production and ACC deaminase activity which indicated the positive interactions among the partners.
Pot culture experiment conducted at National Phytotron Facility, IARI, to evaluate the comparative performance of individual cultures, dual cultures and biofilms. Observations illustrated the positive influence of biofilms on plant growth and biocontrol against M. phaseolina challenged cotton crop. Significant correlation of plant parameters with PPO activity, mortality of cotton plants with MBC and defence enzyme activity was also observed by this study. Field experiments were conducted using selected promising formulations in Rhizoctonia solani infested sick plots at the CICR Research farm, Sirsa, for their biocontrol potential. Lowest seedling mortality was recorded with treatments receiving inoculation of T. viride - B. subtilis and T. viride - P. fluorescens biofilms, which were only 8-12% higher than chemical control measures. This was correlated with the significantly enhanced activity of hydrolytic enzymes like -1,3, -1,4 endoglucanases and chitosanase in plants. This study illustrates that such biofilms may closely mimic natural microbial communities and may represent a more viable inoculation option for integrated pest management strategies in agriculture.