Prior inoculation with non-pathogenic fungi induces systemic resistance topowdery mildew on cucumber plants

A spray inoculation of the first leaf of 2-leaf stage cucumber plants with a non-pathogenic isolate of Alternaria cucumarina or Cladosporium fulvum be fore a challenge inoculation with the pathogen Sphaerotheca fuliginea induc ed systemic resistance to powdery mildew on leaves 2-5. Systemic resistance was expressed by a significant (p < 0.05) reduction in the number of powde ry mildew colonies produced on each leaf of the induced plants, as compared with water-sprayed plants. Systemic resistance was evident when a prior in oculation with each of the inducing fungi was administered 1, 3 or 6 days b efore the challenge inoculation with S. fuliginea. Increasing the inoculum concentration of A. cucumarina or C. fulvum enhanced the systemic protectio n and provided up to 71.6% or 80.0% reduction, respectively, in the number of colonies produced on upper leaves, relative to controls. Increasing the inoculum concentration of S. fuliginea used for challenge inoculation, incr eased the number of powdery mildew colonies produced on both induced and no n-induced plants. Pre-treated plants, however, were still better protected than controls, indicating that the level of systemic protection was related to the S. fuliginea inoculum concentration. The induction of systemic resi stance against powdery mildew by biotic agents, facilitates the development of a wide range of disease management tools.