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Resistance

Resistance in Susceptible Maize to Helminthosporium carbonum Race 1 Induced by Prior Inoculation with Race 2. Frank A. Cantone, Research assistant, Department of Botany and Plant Pathology, Purdue University, West Lafayette, IN 47907; Larry D. Dunkle, USDA/ARS research plant pathologist, Department of Botany and Plant Pathology, Purdue University, West Lafayette, IN 47907. Phytopathology 80:1221-1224. Accepted for publication 9 May 1990. This article is in the public domain and not copyrightable. It may be freely reprinted with customary crediting of the source. The American Phytopathological Society, 1990. DOI: 10.1094/Phyto-80-1221.

Inoculation of leaves of susceptible maize genotypes with the nonpathogenic race 2 of Helminthosporium carbonum at least 10 hr before inoculation with the pathogenic race 1 prevented development of large lesions typical of the susceptible reaction. Appressorium formation, penetration, and hyphal growth by the pathogen were decreased. Addition of HC-toxin (the host-specific toxin produced by pathogenic race 1) to the race 1 challenge inoculum abolished the resistance induced by race 2. Inoculation with H. victoriae, H. turcicum, or Alternaria sp. at least 18 hr before inoculation with H. carbonum race 1 also induced resistance. The results suggest that a general resistance mechanism is activated upon contact of the maize leaf with a potential pathogen and that HC-toxin plays a role in pathogenesis by preventing or overcoming those events.