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Ultrastructure of Penetration of Ethylene-Degreened Robinson Tangerines by Colletotrichum gloeosporioides. G. Eldon Brown, Plant Pathologist III, Florida Department of Citrus, University of Florida, Institute of Food and Agricultural Sciences, Agricultural Research and Education Center, P. O. Box 1088, Lake Alfred, FL 33850; Phytopathology 67:315-320. Accepted for publication 23 September 1976. Copyright 1977 The American Phytopathological Society, 3340 Pilot Knob Road, St. Paul, MN 55121. All rights reserved.. DOI: 10.1094/Phyto-67-315.

The appressorium of Colletotrichum gloeosporioides produced a narrow, threadlike infection hypha less than 0.5 μm in diameter which emerged through a pore in the wall of the appressorium. The pore was surrounded by a funnel-shaped collar that was formed by extensions of the appressorium wall. The cone, comprised of a distinct layer of wall material, was formed upon the collar and was continuous with the wall of the emerging infection hypha. The infection hyphae penetrated the cuticle, and upon approaching the epidermal cell wall, development proceeded in one of three distinct ways. Most frequently, the hyphae enlarged into primordial hyphae, 1-2 μm in diameter, either between or within the epidermal cell wall or lumen. These hyphae, upon septation, gave rise to larger hyphae 3-5 μm in diameter. In other instances, the infection hyphae formed primordial hyphae in the cuticle which grew subcuticularly along the epidermal cell wall and intercellularly between and below the epidermal cells. Occasionally, the infection hyphae penetrated the cuticle and immediately enlarged into the larger 3-5 μm in diameter hyphae. Only minor organelle changes were evident in advance of the invading large hyphae; the most striking change occurred in the chloroplasts.

Additional keywords: postharvest decay, anthracnose, citrus.