Mycorrhizal association: A safeguard for plant pathogen

Abstract

Biological control refers to the potential application of introducing or inhabitant microorganisms to reduce the damage caused by one or more plant pathogens. A continuous interplay between ecosystem and its rhizospheric organisms brings the control of soilborne pathogens which are more difficult to manage. Since last two decades, biocontrol has been gaining considerable interest to maintain sustainable agriculture system. Mycorrhizae are among the most primeval, intimate, and vital association which colonize symbiotically through the roots of various vascular, nonvascular, and crop plants. The arbuscular mycorrhizal (AM) fungi develops a complex mutualistic association with host plant roots via various mechanisms. From the initiation of symbiosis till the formation of arbuscules and/or vesicles, a number of changes occur in plant metabolism, plant nutritional status, and plant resistance. The key indicators of AM fungi for an effective defense response are reduction in the infectivity of soilborne pathogens or suppression of pathogen metabolism or increase in plant’s tolerance toward pathogen. Proposed grounds for a healthier state of plants associated with AM fungi are attributed to (1) improvement in nutritional status of plants, (2) competition between mycorrhiza and pathogen for nutrition and infection sites, (3) modifications in root anatomy and morphology, (4) release of plant root exudates, (5) harboring microbial flora antagonistic to root pathogens, and (6) improved localized as well as systemic resistance in plants. The effective and prolonged mycorrhiza-induced resistance involves various phytohormones, secondary metabolites, pathogen-related proteins, and defense enzymes. Such activation leads to a primed state in plant, which allows quicker and mightier defense response against pathogens. This chapter provides an overview of the underlying mechanisms involved in mycorrhiza-induced disease resistance and priming in plants.