Genetics and QTL mapping of somatic incompatibility and intraspecific interactions in the basidiomycete Heterobasidion annosum s.l.

Somatic incompatibility (SI) is a system by which filamentous fungi can distinguish self from non-self by delimiting the own mycelia from that of other individuals of the same species. In this study, we show that SI in the basidiomycete Heterobasidion annosum sensu lato is controlled by four loci by observing the frequency of somatically compatible pairings in two experiments where isolates were paired in all possible combination. The first experiment utilized 63 heterokaryons each with one unique nucleus chosen from an array of sibling homokaryons paired with one unrelated nucleus of homokaryotic isolate TC-39-7. The second experiment used 39 heterokaryons each with one unique nucleus from the array of sibling homokaryons backcrossed with one of the parental strains (TC-122-12). We observed that SI allelic differences in a pairing alone are not enough to determine the degree of somatic incompatibility. In the first experiment, we also observed other interactions such as hyphal walls in interaction zones, increased exudation of dark-coloured metabolites and increased production of aerial hyphae. QTLs for the respective traits were positioned to a genetic linkage map of the H. annosum genome. Map-based cloning of the corresponding loci will shed much new light on intraspecific interactions in basidiomycetes.