H. Handan Altinok, H. Nilüfer Yildiz
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Biological control, Induced systemic resistance, Rhizobacteria.
Plant Growth Promoting Rhizobacteria (PGPR), colonizing in rhizosphere of plants are able to promote plant growth as well as provide protection against diseases by triggering the defense mechanisms of plants. Bacillus, Pseudomonas and Streptomyces species are licensed as biocontrol agents and/or biological fertilizers and successfully used to control plant pathogens, as a part of integrated disease management. Seed and soil applications of PGPRs are increasing both germination ability and plant resistance to pathogenic microorganisms. Salicylic acid (SA), Jasmonic acid (JA) and ethylene (ET) signaling components are playing an important role on regulation of resistance of plants against various pathogens. SA plays role on pathogen-induced systemic acquired resistance (SAR), while JA and ET take place as key regulators in induced systemic resistance (ISR) promoted by rhizobacteria. Both forms of induced resistance are effective against wide range of pathogens. Several potential defense mechanisms like chitinase, β-1,3 glucanase, pathogenesis-related proteins, phytoalexin accumulation, lignin, callose and hydroxyprolin-rich glycoprotein, protective biopolymer coating are activated in ISR. Siderophores produced by Pseudomonas are able to prevent germination of fungal pathogen spores by binding the iron needed by pathogen. In previous studies, PGPR strains able to fix nitrogen, dissolve phosphate, showing protease activity and produce siderophores and hydrogen cyanide are found to be successful on control of some fungal and bacterial diseases by triggering an increase in synthesis of peroxidase and catalase defense enzymes. This study focused on the roles of PGPRs in ISR.
