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Postharvest Pathology and Mycotoxins

Revised Description of Penicillium ulaiense and Its Role as a Pathogen of Citrus Fruits. G. J. Holmes, graduate research assistant, Department of Plant Pathology, University of California, Riverside 92521; J. W. Eckert(2), and J. I. Pitt(3). (2)professor, Department of Plant Pathology, University of California, Riverside 92521; (3)chief research scientist, Commonwealth Scientific and Industrial Research Organization, Division of Food Science and Technology, North Ryde, New South Wales 2113, Australia. Phytopathology 84:719-727. Accepted for publication 25 April 1994. Copyright 1994 The American Phytopathological Society. DOI: 10.1094/Phyto-84-719.

Penicillium ulaiense causes whisker mold, a recently described post-harvest disease of citrus fruits. A new, more comprehensive description of the fungus and related taxonomic information are given. This description is based on examinations of the type isolate and 33 other isolates from citrus fruits in seven citrus-growing areas of the world. P. ulaiense was confirmed unique from P. italicum, the cause of citrus blue mold, by arbitrarily primed polymerase chain reaction analysis and morphological criteria. P. ulaiense, P. italicum, and P. digitatum (the cause of citrus green mold) showed similar temperature-growth relationships, but P. ulaiense grew more slowly. P. ulaiense was pathogenic but only moderately virulent to commercial varieties of citrus. P. italicum and P. digitatum formed lesions 80 mm in diameter on lemons and oranges three to five times faster than did P. ulaiense. The number of conidia required to produce decay in 50% of inoculated lemons was 100–1,000 times greater for P. ulaiense than those required for P. italicum and P. digitatum. Isolates of P. ulaiense collected in the United States were relatively resistant to the fungicides imazalil, thiabendazole, and o-phenylphenol; mean fungicide concentrations producing 50% inhibition for 17 isolates were 0.7 (±0.2), 45.7 (±14.1), and 12.5 (±5.4) µg/ml, respectively. Growth of all isolates collected in other countries was inhibited completely by 0.2 µg of imazalil or 10 µg of thiabendazole per milliliter. P. ulaiense was isolated frequently from California packinghouses but not from citrus groves.