Abstract
In May 2001, following several years of severe drought, a depressed twig canker was observed on southern live oak (Quercus virginiana) in central Florida. Disease symptoms included twig and branch canker and dieback, distortion of young leaves, and premature leaf drop. Observation of conidia from sporulating acervuli revealed that Coryneum japonicum was associated with the cankers (1,2). The fungus produced abundant, subepidermal, dark brown, linearly arranged acervuli on affected tissues. Conidia were light brown, narrowly fusiform, often curved, and tapered toward an obtuse apex. The conidia had truncate bases and were five to seven distoseptate. Septa were medium to dark brown and sometimes prominent. The length to width ratio of conidia was >4:1. Under normal weather conditions, twig elongation of live oak trees is usually 30 to 60 cm per growing season; however, only 7 to 10 cm was observed on trees affected by C. japonicum. The fungus has been reported on bark and dead twigs of Quercus macrocarpa, Q. gambelii, Q. dilatata, and other species of Quercus in Canada, Pakistan, and the United States (2). To our knowledge, this is the first report of C. japonicum in Florida and on southern live oak trees. A specimen has been deposited in the U.S. National Fungus Collections (BPI number 841441).
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