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Detection of Cladosporium uredinicola in Pustules of Chrysanthemum White Rust (Puccinia horiana). . W. Sheta, USDA, APHIS, PPQ 9317 Tradeport Dr., Orlando, FL 32733. Plant Dis. 80:599. Accepted for publication I March 1996. Copyright 1996 The American Phytopathological Society. DOI: 10.1094/PD-80-0599A.

During the last 2 years, chrysanthemum white rust (Puccinia horiana Henn.) on chrysanthemum cut flowers used in flower arrangements from Brazil was often intercepted by plant protection and quarantine inspectors in Orlando, FL. Close examination of infected cut flowers showed that some pustules were overgrown by Cladosporium uredincola Speg. Morphologically our isolate agrees with the description by Ellis (Cornmonw. Mycol. Inst. 1976) and with all the other isolates of C. uredincola we observed. In 1976, Ellis noted that C. uredincola was a hyperparasite of Puccinia spp. In 1983, J. A. Traquair (1) reported C. uredincola to be a necrotrophic hyperparasite of spores and mycelium of Puccinia violae (Schumach.) DC. In Orlando, FL, during the period between January 1994 and June 1995, 70 samples of chrysanthemum cut flowers infected with P. horiana were examined by stereo-microscope (each sample consisted of a single leaf or stem or flower head with a single rust pustule). Twenty percent of these samples were found to have C. uredincola growing on pustules of while rust with no visible effect on the plant tissues. Some pustules (10%) were completely covered by C. uredincola. Close examination of these pustules by light microscopy (40 and 65x) showed that P. horiana teliospores were penetrated by C. uredincola hyphae. This is the first report of C. uredincola on P. horiana in nature. We may have found a more aggressive strain of C. uredincola than that previously used by Traquair.

Reference: (1) J. A. Traquair et al Can. J. Bot. 62:181, 1984.