Abstract
Basidiocarps of Phellinus tremulae were collected from trembling aspen (Populus tremuloides) in Alberta, Saskatchewan, and Ontario. A mating study based on single spore isolates of 12 of these basidocarps was performed using carrot agar, malt agar, and malt-yeast agar media. Results from carrot agar showed that the fungus is heterothallic and has a tetrapolar mating system. Mating studies on malt agar and malt-yeast agar were inconclusive. The mating factor genes were multiallelic. Compatible and incompatible matings could be recognized microscopically. Radial growth rate of heterokaryon colonies did not differ significantly from that of homokaryon colonies. When genetically different heterokaryotic isolates were paired on agar media a zone of antagonism formed where the two colonies met. No zone of antagonism occurred between genetically identical heterokaryon colonies.