SYSTEMIC RESISTANCE INDUCED BY RHIZOSPHERE BACTERIA

Nonpathogenic rhizobacteria can induce a systemic resistance in plants that is phenotypically similar to pathogen-induced systemic acquired resistance (SAR). Rhizobacteria-mediated induced systemic resistance ( ISR) has been demonstrated against fungi, bacteria, and viruses in Ara bidopsis, bean, carnation, cucumber, radish, tobacco, and tomato under conditions in which the inducing bacteria and the challenging pathoge n remained spatially separated. Bacterial strains differ in their abil ity to induce resistance in different plant species, and plants show v ariation in the expression of ISR upon induction by specific bacterial strains. Bacterial determinants of ISR include lipopolysaccharides, s iderophores, and salicylic acid (SA). Whereas some of the rhizobacteri a induce resistance through the SA-dependent SAR pathway, others do no t and require jasmonic acid and ethylene perception by the plant for I SR to develop. No consistent host plant alterations are associated wit h the induced state, but upon challenge inoculation, resistance respon ses are accelerated and enhanced. ISR is effective under field conditi ons and offers a natural mechanism for biological control of plant dis ease.