Intersterility groups of Heterobasidion annosum and their host specificity in Bulgaria

The occurrence of 46 strains of Heterobasidion annosum from four forest areas in Bulgaria is reported. Three intersterility groups, P, S and F, were identified for the first time in populations of this pathogen in Bulgaria. A strict host specificity of different intersterility groups was observed even in mixed stands. The P group was isolated from Pinus sylvestris and Pinus nigra and occasionally from stumps of Abies alba. It was rare in artificial pine plantations on dry sites, whereas it was more common on more moist sites. The F group caused severe damage on Abies alba but was not found, even as a saprotroph, on admired pines. This is the first report of the F group on Abies alba in the Balkans. The S group was found only on Picea abies.