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Initiation of Induced Nonhost Resistance of Oat Leaves to Rust Infection. T. Tani, Faculty of Agriculture, Kagawa University, Miki, Kagawa 761-07, Japan; Y. Yamashita(2), and H. Yamamoto(3). (2)(3)Faculty of Agriculture, Kagawa University, Miki, Kagawa 761-07, Japan. Phytopathology 70:39-42. Accepted for publication 17 July 1979. Copyright 1980 The American Phytopathological Society. DOI: 10.1094/Phyto-70-39.

Cross-protection experiments were made by first inoculating the abaxial surfaces of primary leaves of oats (cultivar Shokan 1) with oat-noncompatible rust fungi (Puccinia coronata festucae, P. coronata lolii, or P. graminis tritici) and later inoculating the adaxial surfaces with compatible race 203 of P. coronata avenae. The oat nonpathogens were heat-killed at various times after the first inoculation, and the subsequent inhibition of development of the challenge pathogen inside the leaf was used to assay induction of nonhost resistance. Elongation of intercellular hyphae and haustorium formation by race 203 were reduced when the second inoculation was made 12 hr or more, but not 8 hr, after the first inoculation. When stomatal penetration by P. graminis tritici was controlled by exposing plants to light at various times after the first inoculation, it was found that reduction of development of challenge race 203 occurred only after the oat nonpathogen had penetrated and produced substomatal vesicles. The initiation of nonhost resistance was not related to postinoculation time or formation of appressoria over stomates, but it was dependent on the formation of substomatal vesicles.

Additional keywords: Avena sativa, crown rust, cross-protection, stomatal penetration, light radiation.