Modulation of rhizosphere microbial populations using Trichoderma-based biostimulants for management of plant diseases

Trichoderma is the most versatile and widely studied fungal organism that boasts of a number of benefits. It is the biological control agent of choice. This is perhaps due to its ubiquitous nature, ease of isolation and multiplication under laboratory conditions, easy manipulation and adaptation under wide range of climatic conditions, and multifaceted modes of action. Trichoderma is known to manage plant pathogens by multiple modes of action viz., competition, antibiosis, mycoparasitism, and induction of systemic resistance. Besides, it also has an indirect advantage through its biostimulant action, whereby, it produces secondary metabolites that stimulate plant growth resulting in increased root and shoot growth, increased biomass, quality and quantity of produce. These biostimulants have also been implicated in increasing the soil health through bioremediation of problem soils. It has been found that Trichoderma plays a major role in modulation of the rhizosphere microbial populations for the benefit of plants by secretion of secondary metabolites and volatile organic compounds that help in phosphorus solubilization, nitrogen uptake, nutrient utilization, and mineral composition. An important facet is the manipulation of soil microbiota, particularly the plant pathogens, to their disadvantage. An application of Trichoderma is known to reduce the populations of Plasmodiophora brassica, Ralstonia solanacearum, Xanthomonas euvesicatoria, Pseudomonas syringae, etc., among the bacterial plant pathogens. Pythium, Phytophthora, Fusarium, Sclerotinia, etc., are a few of the fungal plant pathogens that have been successfully managed by the use of different Trichoderma species. Inoculations with Trichoderma have been found to influence the eukaryotic and prokaryotic microbial populations in the soil particularly under different fertilization levels and under different types of abiotic and biotic stresses. These properties of Trichoderma make it ideal candidate for bioengineering soil microbiome for the benefit of plant community.