Actinobacteria as Effective Biocontrol Agents against Plant Pathogens, an Overview on Their Role in Eliciting Plant Defense

Pathogen suppression and induced systemic resistance are suitable alternative biocontrol strategies for integrated plant disease management and potentially comprise a sustainable alternative to agrochemicals. The use of Actinobacteria as biocontrol agents is accepted in practical sustainable agriculture, and a short overview on the plant-beneficial members of this phylum and recent updates on their biocontrol efficacies are the two topics of this review. Actinobacteria include a large portion of microbial rhizosphere communities and colonizers of plant tissues that not only produce pest-antagonistic secondary metabolites and enzymes but also stimulate plant growth. Non-pathogenic Actinobacteria can also induce systemic resistance against pathogens, but the mechanisms are still poorly described. In the absence of a pathogen, a mild defense response is elicited under jasmonic acid and salicylic acid signaling that involves pathogenesis-related proteins and secondary plant metabolites. Priming response partly includes the same compounds as the response to a sole actinobacterium, and the additional involvement of ethylene signaling has been suggested. Recent amplicon sequencing studies on bacterial communities suggest that future work may reveal how biocontrol active strains of Actinobacteria can be enriched in plant rhizosphere.