Microbial products and secondary metabolites in plant health.

Plants are continuing challenged by pathogens, either bacteria and fungi. Plant innate immunity set up the plant responses against plant pathogens. However, it is not clear how plants differentiate between pathogens and beneficial bacteria and fungi, such as rhizobia, beneficial bacteria and fungi, as well as other biocontrol and biostimulants. Plant secondary metabolites and compounds in root exudates are produced to recruit plant defense-assisting rhizosphere microbes, contributing to defende them from their pathogens. Soil-borne microorganisms, fungi and bacteria in 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. Plant growth and plant protection are two properties conferred by biocontrol strains and microorganisms. 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. From the strains side, there are plant variety specific mechanisms (sugars, metabolites, genes and proteins) able to attract and facilitate the establishment of the plant growth promoting rhizosphere microbiome. The transfer of specific strains to varieties sensitive to soil-born bacterium Ralstonia solanacearum was shown effective in protecting tomato from the infection. In the last paragraph we review chemical priming and the development of priming chemicals and structure-based approached in synthesis of highly effective primers of plant immunity able to induce and modulate phytohormones in response to pahogens.