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Entomopathogenic Nematodes: Insect biocontrol agents
Abstract
Protection of crop plants from various pest and disease causing organisms is largely dependent on the use of chemical compounds which are toxic to non target organisms and environment. This coupled with its degradation products in environment and human health, strongly necessitates the search for new harmless means of pest control. Entomopathogenic nematodes are one such organism, which parasitize and kill the insects within a short span of 24-48hrs with the help of symbiotic bacteria. Among 23 nematode families, EPNs belongs to two families Steinernematidae and Heterorhabditidae, which have association with bacteria of the genera Xenorhabdus and Photorhabdus, respectively. These nematodes have been used successfully as biological control agents of wide range of insect pests, including a variety of caterpillars, worms, borers, grubs, crane fly, thrips, and beetles, etc. Entomopathogenic nematodes have negligible effects on non target insects and are regarded as exceptionally safe to the environment. These EPNs have the potential to become a good biocontrol agent, if locally isolated and formulated.
Plant growth-promoting rhizobacteria (PGPR) are specialized bacterial communities inhabiting the root rhizosphere and the secretion of root exudates helps to, regulate the microbial dynamics and their interactions with the plants. These bacteria viz., Agrobacterium, Arthobacter, Azospirillum, Bacillus, Burkholderia, Flavobacterium, Pseudomonas, Rhizobium, etc., play important role in plant growth promotion. In addition, such symbiotic associations of PGPRs in the rhizospheric region also confer protection against several diseases caused by bacterial, fungal and viral pathogens. The biocontrol mechanism utilized by PGPR includes direct and indirect mechanisms direct PGPR mechanisms include the production of antibiotic, siderophore, and hydrolytic enzymes, competition for space and nutrients, and quorum sensing whereas, indirect mechanisms include rhizomicrobiome regulation via. secretion of root exudates, phytostimulation through the release of phytohormones viz., auxin, cytokinin, gibberellic acid, 1-aminocyclopropane-1-carboxylate and induction of systemic resistance through expression of antioxidant defense enzymes viz., phenylalanine ammonia lyase (PAL), peroxidase (PO), polyphenyloxidases (PPO), superoxide dismutase (SOD), chitinase and β-glucanases. For the suppression of plant diseases potent bio inoculants can be developed by modulating the rhizomicrobiome through rhizospheric engineering. In addition, understandings of different strategies to improve PGPR strains, their competence, colonization efficiency, persistence and its future implications should also be taken into consideration. © 2022 Centro Regional de Invest. Cientif. y Tecn.. All rights reserved.
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