[en] 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.

[es] En 1980, nuestro grupo de investigaci&oacute;n en la Facultad de Ciencias Forestales de la Universidad de Toronto demostr&oacute; que brinzales j&oacute;venes de olmo de cuatro a&ntilde;os de edad adquirieron resistencia frente a la cepa agresiva del pat&oacute;geno de la grafiosis (Ophiostoma novo-ulmi) cuando previamente se hab&iacute;an inoculado con la cepa no agresiva (O. ulmi) del pat&oacute;geno. Este trabajo se repiti&oacute; en 2000 y 2002 con olmos de entre 15 y 20 a&ntilde;os de edad. En ellos se inocul&oacute; en el tronco, a la altura del pecho, con O. ulmi y posteriormente O. novo-ulmi, imitando el proceso infectivo realizado por los barrenillos del olmo. En general, el ensayo mostr&oacute; que las cepas no agresivas, inoculadas en el tronco de &aacute;rboles de 15 a 20 a&ntilde;os, pueden producir s&iacute;ntomas de la enfermedad, pero que los &aacute;rboles por lo general sobreviven, en contraste con los controles. Estos ensayos indican adem&aacute;s que este tipo de resistencia inducida no confiere inmunidad absoluta o protecci&oacute;n en todas las situaciones, pero s&iacute; que reduce considerablemente la severidad de la enfermedad y protege al &aacute;rbol de infecciones m&aacute;s grave. El trabajo basado en la resistencia inducida en los olmos en nuestro laboratorio condujo al aislamiento de una glicoprote&iacute;na que induce mecanismos de defensa en los &aacute;rboles. La determinaci&oacute;n de los amino&aacute;cidos y de la secuencia de ADN de la glicoprote&iacute;na permiti&oacute; la caracterizaci&oacute;n del gen inductor. Ensayos de campo en brinzales de olmo de cinco a&ntilde;os y en &aacute;rboles de 10 a 15 a&ntilde;os condujeron a la conclusi&oacute;n de que el &eacute;xito del tratamiento inductor en la protecci&oacute;n del &aacute;rbol frente al ataque del pat&oacute;geno depende de la constituci&oacute;n gen&eacute;tica del &aacute;rbol, de su salud y de las condiciones ambientales.