In 1980, our research group at the faculty of Forestry, University of Toronto, demonstrated that young elm seedlings (4 years old) acquired resistance against aggressive strains of the Dutch elm disease pathogen (Ophiostoma novo- ulmi) when they were first inoculated with non-aggressive strains (O. ulmi) of the pathogen. This work was repeated in 2000 and 2002 with elm trees between 15 and 20 years of age. These trees were stem inoculated at breast height with O. ulmi and challenged with O. novo- ulmi, imitating the infection process by the European elm bark beetle. In general, the experiments indicated that non-aggressive strains, inoculated into the stem of 15-20-year-old conditioned trees, may produce disease symptoms but trees generally survive. This is in contrast to the unconditioned controls. These experiments further indicate that this type of induced resistance does not confer absolute immunity or protection under all circumstances but reduces considerably the disease severity and protects the tree from super-infection. Work based on induced resistance in elms in our laboratory led to the isolation of a glycoprotein that elicited defense mechanisms in the tree. Determination of the amino acid and DNA sequence of the glycoprotein resulted in the characterization of the elicitor gene. Field experiments on 5-year-old elm seedlings and 10 to 15 year old trees led to the following conclusions: the success of the elicitor treatment in protecting the tree against pathogen attack depends on the genetic constitution of the tree, its health and on environmental conditions. ; En 1980, nuestro grupo de investigación en la Facultad de Ciencias Forestales de la Universidad de Toronto demostró que brinzales jóvenes de olmo de cuatro años de edad adquirieron resistencia frente a la cepa agresiva del patógeno de la grafiosis (Ophiostoma novo-ulmi) cuando previamente se habían inoculado con la cepa no agresiva (O. ulmi) del patógeno. Este trabajo se repitió en 2000 y 2002 con olmos de entre 15 y 20 años de edad. En ellos ...