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Vegetative Compatibility in Leucostoma persoonii. Gerard Adams, Assistant professor, Department of Botany and Plant Pathology, Michigan State University, East Lansing 48824; Sue Hammar, and Tyre Proffer. Graduate research assistant, and research associate, respectively, Department of Botany and Plant Pathology, Michigan State University, East Lansing 48824. Phytopathology 80:287-291. Accepted for publication 18 September 1989. Copyright 1990 The American Phytopathological Society. DOI: 10.1094/Phyto-80-287.

Isolates of Leucostoma persoonii were paired on various media to determine a suitable medium for differentiating vegetative compatibility (VC) groupings. Barrage reactions were evident only on oatmeal agar as dark lines with pycnidia forming along the zone of mycelial contact between expanding colonies (vegetatively incompatible reaction). Conidia from a single perithecium were in one VC group (VCG). Ascospore colonies derived from individual pycnidia in several stroma on different branch cankers always segregated into several VCGs per perithecium, indicating that the fungus outcrosses and is most likely heterothallic with several alleles controlling vegetative compatibility. Isolates of L. persoonii from cankers on peach trees within an orchard were of numerous VCGs. Isolates from several cankers within one tree and among closely spaced trees usually differed in VC grouping. Spatial clustering of VCGs in an orchard did not appear aggregated. A reappraisal of ascospores as important infective propagules is warranted by the high frequency and dispersed spatial arrangement of VCGs in Michigan peach orchards.

Additional keywords: Cytospora canker, perennial canker, Prunus persica, sexuality.