Somatic incompatibility in basidiomycetes

Somatic incompatibility regulates allorecognition (recognition of nonself) and allorejection following somatic contacts in many groups of organisms. The occurrence of somatic incompatibility and the resolving power of allorecognition probably reflect an evolutionary balance between the costs and benefits of somatic integration with conspecific neighbors and intramycelial anastomoses. In basidiomycetes, somatic incompatibility appears to function primarily in the dominant somatic phase, the secondary mycelium, and is clearly distinct from two other incompatibility systems, sexual incompatibility and intersterility. In laboratory studies, closely related mycelia are apparently recognized as self in many cases. However, allorecognition is almost always evident between different secondary mycelia from nature. Somatic incompatibility has therefore played an important role in concepts of individualism in fungi. In practice, somatic incompatibility in the strict sense (failure of anastomoses and genetic and cytoplasmic isolation) is usually inferred from mycelial incompatibility (macroscopic lines between colonies that can be interpreted as agonistic responses). Although the genetic mechanism is still unclear, multiple loci appear to be involved.