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Hypersensitive Response of Orange-Colored Robinson Tangerines to Colletotrichum gloeosporioides After Ethylene Treatment. G. Eldon Brown, Research Scientist 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 68:700-706. Accepted for publication 18 November 1977. Copyright 1978 The American Phytopathological Society, 3340 Pilot Knob Road, St. Paul, MN 55121. All rights reserved.. DOI: 10.1094/Phyto-68-700.

Mature Robinson tangerines with about 25% external orange color break did not develop anthracnose caused by Colletotrichum gloeosporioides when treated with ethylene to obtain a complete orange color. Histochemical tests of the peel removed after ethylene treatment indicated that phenolics and lignin were present in the flavedo in association with infection hyphae produced by appressoria on the peel surface. Ultrastructural changes occurred in cells up to five cell diameters from the point of penetration. Cytoplasm of these cells contained mitochondria with dilated cristae and chromoplasts that often had indistinct envelopes and homogeneous stroma. The cytoplasm also contained numberous vesicles apparently derived from dilated endoplasmic reticulum and dictyosomes. Vesicles formed by the dictyosomes usually were contained within multivesicular bodies. These bodies frequently were associated with the plasmalemma before electron-dense deposits accumulated at the cell wall. Accumulation of deposits occurred concurrently with collapse of the cytoplasm against the cell wall distal from the area of fungal penetration. Many cells eventually became occluded with electron-dense material which surrounded hyphae in the invaded cells.

Additional keywords: phenolic materials, postharvest decay, citrus, histochemistry, ultrastructure.