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Ultraviolet Light-Induced Instability of Vegetative Compatibility Groups of Cryphonectria parasitica. R. Rizwana, Graduate research assistant, Department of Environmental and Forest Biology, State University of New York, College of Environmental Science and Forestry, Syracuse 13210-2788; W. A. Powell, Assistant professor, Department of Environmental and Forest Biology, State University of New York, College of Environmental Science and Forestry, Syracuse 13210-2788. Phytopathology 82:1206-1211. Accepted for publication 23 June 1992. This article is in the public domain and not copyrightable. It may be freely reprinted with customary crediting of the source. The American Phytopathological Society, 1992. DOI: 10.1094/Phyto-82-1206.

The main objective was to study the effect of ultraviolet (UV) light on vegetative compatibility in the fungus Cryphonectria parasitica. A procedure was developed to detect individual incompatible colonies from cultured lawns of compatible colonies. Incompatibility reactions were observed when protoplasts from two different vegetative compatibility (v-c) groups were mixed and plated on a suitable medium containing red food color. With this technique, incompatible colonies were observed in plated protoplasts prepared from UV light-treated mycelium of a single v-c group. UV-treated conidia originating from a single v-c group also produced incompatible colonies detected by this procedure. Single conidial isolates from incompatible colonies were tested for vegetative compatibility, confirming a change in v-c grouping. The isolates with changed v-c groups were unstable, reverting to their original v-c group or changing to different v-c groups. The unstable v-c group mutants changed throughout the course of this study. Because of this instability, the v-c groups of most of the changed isolates could not be identified. These observations suggest that UV light induces v-c group instability. This phenomenon may contribute to the large diversity of v-c groups in natural populations of C. parasitica.