VIEW ARTICLE

Cytology and Histology

Mode of Parasitism of Alternaria brassicae by Nectria inventa. A. Tsuneda, Graduate Student, Department of Plant Science, University of Alberta, Edmonton, Alberta, Canada T6G 2E3; W. P. Skoropad(2), and J. P. Tewari(3). (2)(3)Professor, and Research Associate, respectively, Department of Plant Science, University of Alberta, Edmonton, Alberta, Canada T6G 2E3. Phytopathology 66:1056-1064. Accepted for publication 26 January 1976. Copyright © 1976 The American Phytopathological Society, 3340 Pilot Knob Road, St. Paul, MN 55121. All rights reserved.. DOI: 10.1094/Phyto-66-1056.

The Verticillium state of Nectria inventa is a destructive mycoparasite of Alternaria brassicae. Parasitism occurs either by means of contact without penetration or by penetration of the host. The parasitic hyphae induce abnormal responses in host cells upon contact. A reaction zone that consists largely of an electron-transparent matrix with dispersed tubule-like electron-dense material develops between the cell wall and the invaginated plasma membrane. The tubule-like elements subsequently aggregate to form electron-dense deposits below the cell wall. The affected cell forms a septal plug, accumulates membranes in some cases, and finally degenerates. Nectria inventa hyphae penetrate mainly the conidial cells of A. brassicae. This process appears to be primarily chemical in nature. The cytoplasm of the penetrated cell becomes progressively less dense and the cell eventually appears to be empty.