Plant growth promoting potential of bacteria isolated on N free media from rhizosphere of Cassia occidentalis

Plant growth promoting rhizobacteria (PGPR) are an attractive eco-friendly alternative to chemicals in agriculture. While the rhizospheres of crop plants have been well studied with the objective of screening PGPR, weeds, which play an important role in maintaining ecological balance, have largely been ignored. The rhizosphere of a luxuriantly growing, medicinal weed, Cassia occidentalis was analysed by enumerating PGPR on N free media from the most diverse stage of plant (determined by profiles obtained on denaturing gradient gel electrophoresis). Each isolate was tested for other plant growth promotion assays including production of cellulase, indole acetic acid (IAA), ammonia, HCN, siderophore and chitinase to select for ones possessing multi-trait plant growth promoting (PGP) properties. Selected isolates were used for bacterization of Vigna radiata and Vigna mungo to evaluate their efficacy in promoting plant's growth in seedling germination and axenic pot conditions. Thirty five isolates were analysed further for the array of PGP properties they exhibit. A total of 6 isolates were shortlisted on the basis of maximum traits positive, amount of phosphate solubilized and IAA produced. V. radiata responded well to seed bacterization during seedling germination. A maximum increase of approximately 36 and 60 % was observed for shoot and root length, respectively in V. radiata in axenic pot culture over control plants. Extensive branching of roots was also observed with isolate NL, which produced the maximum amount of IAA. Present study investigated the plant growth promoting isolates obtained on N free media in the rhizosphere of C. occidentalis, which have the potential to be used as inoculants for other crops. This provides a new dimension to the significance of weeds in agricultural ecosystems. The study opens up possibilities for utilization of this property of weeds in plant growth promotion, and subsequent enhancement of yield for agricultural crops.