Natural disease resistance of plants is based on pre-existing and inducible defense systems that provide protection against a wide range of potential pathogens. Induced resistance to plant pathogens is a widespread phenomenon that has been intensively investigated with respect to the underlying signaling pathways as well as to its potential for plant protection. Elicitation of systemic acquired resistance or induced systemic resistance results in a state of heightened defense induced throughout a plant following local infection by pathogens or interaction with beneficials. Thus, plants respond with activation of a complex net of signaling cascades that leads to the systemic expression of a long-lasting disease resistance to a broad spectrum of plant pathogens.
The activation of defense responses is associated with ecological fitness cost, so plants need regulatory mechanisms to effectively and efficiently adapt to changes in their environment. A crosstalk between different signaling systems, for example, between salicylic acid-dependent and jasmonate-dependent pathways, provides a fine-tuning of plant defense responses to the pathogen challenges.
Colonization of plant roots with some beneficial soil microorganisms or plant infection with necrotizing pathogen can result in a specific state of plants called priming. This state is also induced by various natural and synthetic compounds. In the case of priming, a potentiated response develops rather on the subsequent attack of a pathogen than on the initial impact. During priming, genes responsible for the defense response development are considered to be derepressed that results in their rapid and intensive expression in reply to the pathogen attack. Primed plants are efficiently protected against biotic stress without major trade-off effects on their commercially and ecologically important traits.
The aim of this Research Topic is to create a platform for scientists studying the mechanisms of action of different biocontrol agents in plants. In addition, the studies presented in this Topic will probably facilitate the understanding how a plant opts for its defense mechanisms and activates any of them against different pathogens.

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