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Reduction of Laccase Activity in dsRNA-Containing Hypovirulent Strains of Cryphonectria (Endothia) parasitica. Daniel Rigling, Swiss Federal Institute of Forestry Research, 8903 Birmensdorf, Switzerland; Ursula Heiniger(2), and Hans R. Hohl(3). (2)Swiss Federal Institute of Forestry Research, 8903 Birmensdorf, Switzerland; (3)Institute of Plant Biology, University of Zurich, Switzerland. Phytopathology 79:219-223. Accepted for publication 4 August 1988. Copyright 1989 The American Phytopathological Society. DOI: 10.1094/Phyto-79-219.

Double-stranded RNA (dsRNA) was detected in hypovirulent but not in virulent strains of Cryphonectria (Endothia) parasitica isolated in Switzerland. To test for phenol oxidase activity we grew the strains on malt extract agar containing tannic acid (Bavendamm test). All virulent strains produced a strong color reaction, indicating phenol oxidase activity, whereas hypovirulent strains showed weak or no activity. Transfer of dsRNA into virulent strains via hyphal anastamosis resulted in transfer of hypovirulence as tested in the field and loss of phenol oxidase activity. Phenol oxidase is secreted into the medium at the advancing edge of the fungal colony. The enzyme was identified as phenol oxidase of the laccase type. The results suggest that laccase might play a role in pathogenicity of C. parasitica and is affected by dsRNA.