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Studies on Wheat Stem Rust Resistance Controlled at the Sr6 Locus. III. Ethylene and Disease Reaction. J. M. Daly, Department of Biochemistry and Nutrition, University of Nebraska, Lincoln 68503; Paul M. Seevers(2), and Paul Ludden(3). (2)(3)Department of Biochemistry and Nutrition, University of Nebraska, Lincoln 68503. Phytopathology 60:1648-1652. Accepted for publication 15 June 1970. DOI: 10.1094/Phyto-60-1648.

Peroxidase activity can be induced in resistant lines of wheat by infection with race 56 of Puccinia graminis tritici. Since ethylene also can induce high peroxidase activity, resistant and susceptible infected lines carrying the respective Sr6 alleles were treated with ethylene. Treatment caused infected susceptible leaves to increase in peroxidase activity to levels above the activity exhibited by infected, resistant untreated leaves, but treated leaves remained susceptible. In contrast, ethylene-treated resistant leaves at 20 C reverted to complete susceptibility, despite the fact of high peroxidase activity induced by ethylene and infection. There were no significant differences in pustule numbers among treated or untreated resistant and susceptible leaves. It is concluded that total peroxidase activity is not causally related to resistance, expressed either as infection type or as pustule density. Susceptible infected leaves had much higher rates of ethylene production than leaves showing a resistant reaction, although the latter had rates significantly above healthy control leaves. The higher rates of ethylene production in susceptible reactions are consistent with the changes in infection type produced by ethylene, but are not consistent with the activation of peroxidase either by ethylene or by resistant reactions. The results raise the question as to whether it is resistance or susceptibility that is induced during the infection process in rust reaction controlled by Sr6 alleles.

Additional keywords: Triticum, obligate parasitism.