Plant immune system activation: Induction of resistance and disease reduction

Abstract

This paper makes a brief review of the activation of the plant immune system, which has been extensively studied over the last 50 years. The activation of the immune system of plants is induced not only by plant pathogens (microorganisms, nematodes and insects) but also by beneficial rhizosphere microorganisms and chemical stimuli, and it plays an important role in the reduction of a wide range of plant diseases and pests. Two main routes are involved: the salicylic-dependent or systemic acquired resistance (SAR) route

and the salicylic-independent or induced systemic resistance (ISR) route. The first route is linked to plants’ response to pathogens, with the involvement of the hormone salicylic acid and pathogenesis-related proteins. The second route is related to beneficial organisms, the involvement of jasmonic acid and ethylene hormones. Likewise, experimental results are presented that evidence the involvement of other plant hormones in the modulation of both routes. Rhizosphere-competent bacteria or fungus like Trichoderma asperellum, strain T34, bolster defence responses systemically and enhance the defensive capacity of plants against a wide range of pathogens. The alteration of root exudates by the attack of a pathogen has an effect on root microbial populations. Plants can maintain the populations of beneficial microorganisms close to their roots by exuding specific compounds. The use of olive mill compost as plant growth media stimulates plant defence response by SAR by producing a “eustress”, which is a kind of mild beneficial stress that is free of any detrimental effect on growth and exerts a favourable effect on plants’ defence capacity against pathogens.