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Etiology

Pathogenicity of Two Biotypes of Elsinoë fawcetti to Sweet Orange and Some Other Cultivars. J. O. Whiteside, Professor of Plant Pathology, University of Florida, Institute of Food and Agricultural Sciences, Agricultural Research and Education Center, P. O. Box 1088, Lake Alfred, FL 33850; Phytopathology 68:1128-1131. Accepted for publication 2 March 1978. Copyright © 1978 The American Phytopathological Society, 3340 Pilot Knob Road, St. Paul, MN 55121. All rights reserved.. DOI: 10.1094/Phyto-68-1128.

All 24 single-conidium isolates of Elsinoë fawcetti obtained from susceptible cultivars of citrus in different Florida groves and nurseries were pathogenic to rough lemon shoots, grapefruit shoots and fruit, and Murcott fruit; but only 13 of them incited scab on sour orange shoots. It has been customary to refer to scab caused by E. fawcetti as sour orange scab but this needs revision in the light of these findings. None of the isolates was pathogenic to shoots of sweet orange. Fruits of sweet orange and Temple were infected only by the 13 isolates that were pathogenic to sour orange shoots. In the field, scab is very common and often severe on fruit of the Temple cultivar but it seldom appears on sweet orange, even though both cultivars are susceptible to the same biotype of E. fawcetti. The rare occurrences of scab on sweet orange fruit apparently is due, at least partly, to the poor chances for inoculum carry-over in the tree canopy from one crop to the next, rather than to any high inherent resistance of the fruit rind to infection.