Microbe-Induced Resistance Against Pathogens and Herbivores: Evidence of Effectiveness in Agriculture

This chapter presents a summary of the results of experiments conducted in Alabama and Florida over a five year period to evaluate strains of plant growth-promoting rhizobacteria (PGPR) for induction of resistance against insect-transmitted diseases on field-grown cucumber and tomato. Experiments with cucumber demonstrated that treatment with PGPR significantly reduced the incidence of wilt symptoms caused by the bacterial pathogen Erwinia tracheiphila, and also reduced numbers of the cucumber beetle vectors of the bacteria. Cotyledons from PGPR-treated plants contained significantly lower concentrations of cucurbitacin, a secondary plant metabolite and cucumber beetle feeding stimulant, than untreated plants. The PGPRinduced change in cucurbitacin metabolism may be associated with the production of other plant defense compounds during the induction of a systemic plant defense response. Subsequent studies with tomato were conducted to identify PGPR strains for induction of systemic resistance against cucumber mosaic cucumovirus (CMV} and whitefly-transmitted tomato mottle virus (ToMoV). Tomatoes treated with PGPR demonstrated a reduction in the development of disease symptoms, and often a reduction in the incidence of viral infection and increase in tomato yield. While preliminary, the results of these experiments in cucumber and tomato demonstrate that PGPR-mediated induced resistance represents a viable and environmentally-friendly approach to crop disease management, particularly for insect-transmitted diseases which are often difficult or impossible to control with pesticides.