**6.5 Induced resistance**

Rhizospheric microbes protect the plant not only through their antagonistic properties but also help the plant to defend itself from the pathogenic attack. The term induced resistance is meant for the induced state of resistance in plants triggered by various biological inducers and subsequent protection of non-exposed plant parts against future attack by pathogenic microbes of any kind. Induction of resistance can be local and/or systemic in nature depending on various factor such as types, source, and stimuli. There are two types of induced resistance namely SAR and ISR which provide long-lasting resistance against plant pathogens. Systemic acquired resistance (SAR) is mediated by salicylic acid (SA) and produced following pathogen infection and leads to the expression of pathogenesis-related (PR) proteins. PR proteins include enzymes which may act directly to lyse invading cells, reinforce cell wall boundaries to resist infections, or induce localized cell death [78]. Induced systemic resistance is the process of active resistance against pathogen and is induced upon by colonization of beneficial microbes like PGPF and PGPR or infection by some specific pathogen. It does not rely on SA but depends on the pathways regulated by jasmonate and ethylene [86]. Pathogenic microorganisms trigger a wide range of defense mechanisms in plants through ISR. The major changes occurs in root of the host pant through ISR are: (1) Strengthening of epidermal and cortical cell wall; (2) increase in levels of defense enzyme such as chitinase, polyphenol oxidase, peroxidase, phenylalanine; (3) increase in phytoalexin production and (4) expression of stress related genes [80]. ISR extending up to the shoots from roots protects the unexposed parts of plants against pathogenic attacks by microorganisms in future [87]. The induced resistance is elicited by various beneficial and non-beneficial organisms and regulated by signal pathways, where plant hormones for example play a vital role in inducing the resistance which is regulated by networks of interconnected signaling pathways [88]. Several *Pseudomonas* spp. and *Bacillus* spp. participate in induced systemic resistance (ISR) in a wide range of plants against different pathogens [89]. The PGPR like *Pseudomonas aurantiaca* has been reported to induce the immunity in maize apart from growth promotional activities [90]. Many fungal biocontrol agents such as *Trichoderma* spp., *Penicilliumn simlicissmum* and *Phoma* spp. have also been found to elicit the induced systemic resistance [91].
