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Effects of Triphenylphosphite on Bean Rust Development. G. Rusuku, Faculté des Sciences Agronomiques, 5800 Gembloux, Belgium. P. Lepoivre, M. Meulemans, and J. Semal, Faculté des Sciences Agronomiques, 5800 Gembloux, Belgium. Plant Dis. 68:154-156. Accepted for publication 22 August 1983. Copyright 1984 The American Phytopathological Society. DOI: 10.1094/PD-68-154.

Triphenylphosphite (TPP) at 125 μg/ml, when sprayed onto bean leaves 2 days before inoculation with Uromyces phaseoli, prevented formation of rust pustules. Spore germination, growth of germ tubes on the leaf surface, formation of appressoria, penetration through stomata, formation of substomatal vesicles, development of infection hyphae, and subsequent formation of haustorial mother cells proceeded normally in TPP-treated leaves. However, no haustoria were formed. Both α-aminooxyacetate (an inhibitor of the phenylpropanoid pathway) and cycloheximide (an inhibitor of protein synthesis) largely suppressed the inhibitory effect of TPP when applied to TPP-treated bean leaves 1 day before inoculation. Apparently, TPP triggered a resistance mechanism that prevented formation of haustoria in treated bean leaves inoculated with U. phaseoli.