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Infection Cushion Development by Rhizoctonia solani on Cotton. V. N. Armentrout, Biological Sciences Department, California State Polytechnic University, Pomona 91768; A. J. Downer, University of California Cooperative Extension, Ventura 93009. Phytopathology 77:619-623. Accepted for publication 1 October 1986. Copyright 1987 The American Phytopathological Society. DOI: 10.1094/Phyto-77-619.

Infection cushions produced by Rhizoctonia solani AG-4 form on seedling cotton hypocotyls 21 hr after inoculation. Hyphae align in grooves between epidermal cells and produce lateral branches. These branches often terminate in a “foot,” or T-shaped branch. Tips from these branches elongate to become hyphae parallel to the first. Accumulations of axial hyphae and lateral branches form the cushion. A mucilage-like material is observed, which presumably allows hyphae of the fungus to adhere to the plant surface and to each other. Many hyphal tips form on the underside of the cushion for penetration of the hypocotyl. These developmental steps and the architecture of the cushion that results from them should be considered in interpretation of experimental studies regarding cushion formation.

Additional keywords: infection structure, mucilage.