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Some Factors Affecting the Occurrence and Development of Foot Rot on Citrus Trees. J. O. Whiteside, Associate Plant Pathologist, Agricultural Research and Education Center, Institute of Food and Agricultural Sciences, University of Florida, Lake Alfred 33850; Phytopathology 61:1233-1238. Accepted for publication 20 May 1971. DOI: 10.1094/Phyto-61-1233.

No infection of suberized stems occurred in greenhouse tests on sweet orange and rough lemon seedlings inoculated with zoospores of Phytophthora parasitica except when large numbers of zoospores were applied to wounds made through the outer bark. The fungus was able, however, to penetrate young intact stems in which the periderm had not yet developed. Following inoculation of Page and Pineapple orange trees in the field, some trees that were not visibly wounded developed foot rot, and in these cases infection probably occurred through naturally formed breaks. Both naturally and mechanically induced breaks in the outer bark were detected by observing the penetration of triphenyltetrazolium chloride. Zoospores settled in larger numbers on exposed parenchymatous tissue than on the suberized bark. No penetration of intact bark by germ tubes was ever observed. Wounds were invaded most easily while still fresh. In greenhouse tests, foot rot seldom appeared on stems wounded more than 10 days before inoculation. Foot rot development was favored by covering the infected part of the trunk with soil.

Additional keywords: inoculation technique.