Pesticide Tolerant Rhizobacteria: Paradigm of Disease Management and Plant Growth Promotion

Abstract

Plant growth-promoting rhizobacteria (PGPR) are soil bacteria, colonizing rhizospheric region of plants, which have the ability to enhance plant health and promote plant growth by increasing seed emergence, plant weight, and yields to a wide variety of crops either through direct action or via biological control of plant diseases. PGPR improve plant growth by either fixing atmospheric nitrogen; solubilizing insoluble phosphates and iron and producing plant growth regulators (PGRs) like auxins, gibberellins, cytokinins, etc.; or suppression of deleterious root-colonizing microorganisms including plant pathogens through antibiosis, i.e., production of fungitoxic compounds, competition with pathogenic microorganisms for nutrients by producing siderophores, or niche exclusion. Indiscriminate use of different chemicals in the form of fertilizers and pesticides targeting to increase the agricultural produce for ever-increasing population outburst has led to the contamination of the groundwater, soil, and sediments. Accretion of diversified range of chemicals in significant quantities has a direct impact not only on the living beings but also on the environment. The ecological balance of the soil microorganisms has been distorted which show the negative impact on their rhizospheric competence. When exogenous PGPR are applied in this pesticide-infested soil, they not only hardly show their plant growth-promoting or disease-suppressing activities but also might not survive at all. Isolation of native PGPR from the pesticide-challenged rhizospheric soils mostly shows pesticide-tolerant/degrading properties. These PGPR might show the rhizospheric competence in similar pesticide-infested soil. These strains easily acclimatize in the pesticide-contaminated microenvironment in soil and show their plant growth-promoting and pathogen-suppressive activities.