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Mode of Penetration of Epidermal Cell Walls of Vicia faba by Botrytis cinerea. W. E. McKeen, Professor, Department of Plant Sciences, The University of Western Ontario, 1151 Richmond Street, London, Ontario, N6A 3K7, Canada; Phytopathology 64:461-467. Accepted for publication 9 October 1973. DOI: 10.1094/Phyto-64-461.

Infection of Vicia faba leaves by Botrytis cinerea, a facultative parasite, was studied by means of light and electron microscopy, and histochemical staining. The first indication that infection was about to occur was the turning down of the tip of the germ tube until it contacted the cuticle. The tip of the germ tube was held firmly against the cuticle by means of mucilage which spread some distance (10-15 µm) around the germ tube. Then a pore developed in the fungal wall at the center of the contacting tip of the germ tube. The plasmalemma which covered the infection peg was pressed against the host cuticle and covered the blunt infection peg as it progressed through the cuticle. The cuticle appeared to be enzymatically dissolved rather than mechanically broken because a sharp clean pore without curled edges was made through the cuticle, and the infection peg did not cause an indentation of the cuticle or epidermal wall during penetration. Immediately after passage through the cuticle the epidermal wall began to degrade, split into two or more layers, and the cuticle was pushed upwards and sometimes separated from the epidermal wall. Esterase activity was histochemically detected at the tip of germ tubes 7 h after inoculation (the time of cuticle penetration) but not from 16-23 h after inoculation.

Additional keywords: chemical infection, mechanical infection.