EFFECTS OF INSECTICIDES ON PLANT GROWTH PROMOTING RHIZOBACTERIA ASSOCIATED WITH PEA PLANT (PISUM SATIVUM)

Abstract

The unchecked and excessive use of toxic and harmful insecticides in agricultural practices has become a widespread environmental concern and these chemicals affect the agricultural products adversely, while on the other hand, the bacteria associated with the root system of the plant provides benefits to the plants in terms of their growth promoting abilities and are being used for enhancing plant growth. This study was designed to assess and evaluate the effect of commercially used insecticides on the growth promoting abilities of Plant Growth Promoting Rhizobacteria (PGPR) associated with pea plant. These two coursed studies firstly evaluated the effect of the insecticides on PGPR strains in the laboratory, where Indole Acetic Acid and Nitrogen Fixation were taken as the parameters of interest. The resulting data revealed that IAA production was the highest for the PGPR strains without any stress while with insecticide stress, it was reduced and was concentration dependent where higher concentration resulted in significant decrease (54.02≤15.6 µg/mL). Nitrogen fixation was significantly reduced with imidacloprid stress. The second course for the experimental study was the Completely Randomized Design (CRD) pot experiment where the soil was given insecticidal stress. The nutrient content analysis of the amended soil (NPK) yielded data where the nutrient content was reduced, albeit the reduction was not statistically significant for N-Nit (848.98≤600.14 ppm), Pho (13.30≤0.11 µg/mL) and Pot (208≤0.3 µg/mL). The plants harvested after the completion of the CRD experiment were analyzed for their physiochemical properties, including fresh weight (11.49≤2.84 g), dry weight (1.89≤0.375 g), chlorophyll content (45.133≤37.4 µmol m-2) and Nit (97.45≤86.713 %), Pho (15.421≤3.1357 µg/mL), and Pot (3.8433≤0.59 %). The resulting data was also statistically analyzed and yielded results that revealed that there was a significant reduction in the values of all these parameters under insecticide stress while the PGPR strains gave much higher values without any stress. The results of all the overall study indicated that plants without the insecticide stress showed high values for all the physical and chemical properties, the PGPR strains also produced effective results as strain 98 performed better than strain 92 in most of the parameters without the insecticide stress in soil while for physical and chemical characteristics, strain 92 was better able to tolerate increasing insecticidal stress. But the insecticides, particularly in iv concentrations higher than the recommended doses, affected the growth promoting activities of the both the PGPR strains, especially strain 98, in the order Imidacloprid> Acetamiprid> Lambda-Cyhalothrin.