Vegetative Compatibility inLeucostoma persoonii

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Abstract
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 progagules is warranted by the high frequency and dispersed spatial arrangement of VCGs in Michigan peach orchards.