Investigating the Role of PGPM in Assisting Plant Growth Under Stress Caused by Organophosphate Pesticide- Phorate

Abstract

Farmers across the world face the challenge of compromised agriculture productivity due to abiotic stress. Residual pesticides accumulating in the soil rhizospere are often found to cause a chemical imbalance in the soil microclimate resulting in chemical toxicity and osmotic stress. Plant growth promoting microorganisms (PGPM) are popularly studied for their ability to enhance plant growth by providing stress tolerance to plants. The present study is to investigate the role of PGPM in reducing toxicity caused due to accumulation of organophosphate pesticide (OPP) - Phorate. Isolation, evaluation and selection of best phorate tolerant PGPM strains was done by various rounds of purification and biochemical characterization assays. Isolates of PGPM from the rhizospere of Pearl Millet-PB, Maize PM, Pigeon Pea-PA, Sugarcane-PS and Sorghum-PJ were studied for their ability to tolerate a wide range of OPP (150 ppm to 1050 ppm). Subsequently, in vitro plant bioassay was performed to select the isolate that can provide best growth promotion property to host plant when challenged with pesticide phorate. The parameters studied to evaluate growth promotion abilities were percentage germination, seed vigor and total biomass. We were successful in isolating, evaluating and selecting best PGPM strains for providing tolerance to host plant under phorate induced stress. Out of the four isolates tested, isolates PM and PB showed better tolerance to phorate and recorded higher LD50 and MIC values as compared to other isolates. When compared with control, OPP stress subjected PM and PB showed best tolerance to OPP with LD50 981 ppm/unit OD and 1249 ppm/unit respectively and MIC values as 1050 ppm. However from the plant bioassay it was evident that between PM and PB, PM was a better bioinoculant as it contributed to plant growth with respect to all studied parameters (viz. percentage germination and seed vigor) where as PB stood as second best at providing growth support to host plants when challenged with phorate. Culture isolate PM emerged as the choicest isolate that can be further explored as a potential bioinoculant under pesticide stressed conditions. Isolate PB, with comparable pesticide tolerance (very near MIC & LD50 values) as PM, was clearly outcompeted by PM when it came to supporting plant growth (evident from in vitro plant bioasaay). A Culture having high pesticide tolerance under in vitro conditions, may or may not possess the ability to support plant growth when used as a bioinoculant at high pesticide concentrations. The study clearly emphasizes the importance of host response studies for making selection of rhizobacteria for the purpose of remediating pesticides. PB with comparable pesticide tolerance with PM under in vitro conditions was clearly outcompeted by PM when it came to supporting plant growth (as evident from results of plant bioasaay). The study offers proof that, inoculation with carefully selected pesticide tolerant PGPM can have a positive impact on plant growth even under high concentration of organophosphate pesticides. © 2015 iGlobal Research and Publishing Foundation. All rights reserved. NOTE: Full length manuscript of Gupta et al. Investigating the Role of PGPM in Assisting Plant Growth