Microbial products and secondary metabolites in plant health

Abstract Microbial strains are used as successful biological control agents for contrasting plant pathogens, mainly phytopathogenic fungi, and as biostimulants. The chapter describes the interactions at molecular level between plants and beneficial microorganisms and the pathways in common with receptors recognizing pathogens and leading to Pattern Triggered Immunity. Plants recognize and interact with the beneficial microbiota, through attenuation of pattern triggered immunity and effector triggered immunity. Plants discriminate among effectors and elicitors from beneficial microorganisms. Plants are continuing challenged by pathogens, either bacteria and fungi. Plant secondary metabolites, sugars, and proteins in root exudates are produced to recruit plant defense-assisting rhizosphere microbes, contribute to defend them from their pathogens. Soil-borne microorganisms, fungi and bacteria of the rhizosphere, play an important role in suppression of plant diseases by direct control of root and foliar pathogens, as well as through induction of systemic resistance in plants. Microbial strains isolated from resistant tomato plants when inoculated to varieties sensitive to soil-borne bacterium Ralstonia solanacearum were effective in protecting tomato from the infection. Transfer of microbiomes can be an effective approach to attenuate plant diseases and to induce the formation of suppressive soils. Fungal metabolites contribute to plant health, and fungal extracts applied to plants have been shown effective in recovery from pathogen attack. In the last paragraph we review chemical priming and discuss new priming compounds, and structure-based approached in synthesis of new efficient compounds priming plant immunity, that can be exploited in agriculture through spraying applications.