Something in the agar does not compute: on the discriminatory power of mycelial compatibility in Sclerotinia sclerotiorum

Mycelial compatibility, the ability for fungal isolates to grow together and form one single colony, was defined for Sclerotinia sclerotiorum nearly 30 years ago and has since been used as a marker to describe clonal variation in population genetic studies. While evidence suggests an associative relationship between mycelial compatibility and vegetative compatibility, contemporary research has treated these traits as analogous. As molecular markers have been developed to describe genetic variation, researchers combined these with the mycelial compatibility groups to assess and to define clonal lineages. However, several inconsistent relationships between mycelial compatibility groups, haplotypes, and even vegetative compatibility groups have been observed throughout the literature, suggesting that mycelial compatibility may not accurately reflect self-recognition. We argue that the Sclerotinia community needs to move beyond using MCG data in population genetic studies.