Rhizosphere Population Dynamics and Internal Colonization of Cucumber by Plant Growth-Promoting Rhizobacteria which Induce Systemic Resistance to ColletotrichumOrbiculare
Plant growth-promoting rhizobacteria (PGPR) are root-colonizing bacteria which exert a beneficial effect on plant development. The reported beneficial effects of PGPR include plant growth promotion (Kloepper et al., 1991) and reductions in the incidence of soilborne diseases (Kloepper, 1991; Weller, 1988). Due to their effects on crops, PGPR hold promise for use in integrated strategies for implementing low-input sustainable agriculture. Implementation of large-scale field use of these bacterial inoculants will require decreasing the variability of field performance which appears to be innate with most inoculants consisting of single bacterial strains. One approach to reducing variability is to use mixed inoculants consisting of two or more bacterial strains with different mechanisms. This approach depends upon having identifiable differences in mechanisms. Most of the PGPR and bacterial biological control agents which have been reported to date were first selected by antibiosis in vitro toward fungal pathogens (Weller, 1988) and then tested for biological control activity in disease assays with the host plant. Hence, it is not surprising that most suggested mechanisms for growth promotion and biological control by rhizobacteria involve antibidtics, siderophores, HCN, or other compounds which can be broadly called antifungal compounds (Kloepper, 1991; Weller, 1988). Competition for infection sites or nutrients (other than iron) and parasitism are other mechanisms which have been reported to relate to biological control with a few rhizobacterial strains (Kloepper, 1991).
KeywordsBiological Control Systemic Resistance True Leaf Cyanic Acid Soilborne Disease
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