Postmating barriers refer to the inviability and sterility that is often observed in hybrids. In such cases, crosses between evolutionary lineages occur and lead to the production of hybrids, but they exhibit little ability to grow and develop or to further produce functional offpsring. For instance, crosses among Neurospora species led to the production of few and abnormal fruiting structures (perithecia) and ascospores viability was low (Dettman et al., 2003b). Relatively few studies have reported hybrid inviability or sterility in mushrooms because the experimental induction of basidiocarps is often very difficult (unfortunately for mushroom eaters). It is therefore difficult to analyse experimentally the progeny of hybrids in mushroom-forming fungi.