Interactions between 42 higher fungi and six strains of Heterobasidion annosum (Fr.) Bref., representing P and S intersterility groups were studied in vitro. Part of the higher fungi was represented by strains of ectomycorrhizal fungi indigenous to old disease centres caused by H. annosum in pine stands. Variation in antagonism to the pathogen was observed both within and between the species. The antagonism was dependent on growth rates of fungi in control. Fungi growing faster displayed a greater ability to arrest the development of the pathogen mycelia. The same tendency was observed in the strains of H. annosum, which generally grew faster and their growth was restricted less than that of higher fungi. Two strains of an ectedomycorrhizal fungus Mrg X, accompanied by a helper bacteria reduced mycelial extension of H. annosum by 72% and 76%. Among ectomycorrhizal fungi, the most effective antagonists were strains of Xerocomus subtomentosus, Amanita muscaria, A. citrina and Laccaria laccata. Three various types of interaction between the studied fungi were observed. Inhibition zone between interacting mycelia appeared often, however the fungi displayed this antagonistic property not to all strains of the pathogen. Although mycelia of H. annosum invaded colonies of the other fungi frequently, in none of the treatments growth of the higher fungus over the opposing colony of the pathogen was observed.
Prepenetration and penetration phenomena after inoculation of roots of Pinus sylvestris seedlings grown in vitro with the P-, S- and F-group isolates of Heterobasidion annosum were observed using scanning electron microscop. There were no differences in the behaviour of hyphae and in the appearence of mycelia formed by the three IS-group isolates. Four types of the root penetration by hyphae were observed. In the first, the entrace of hypha into root was achieved throught tiny pore formed in walls of the cortical cells. In the second, swellings resembling appressoria were formed by the hyphal tips at the points of contact with the root surface. In the third, the hyphae penetrated cells through holes in eroded areas of roots, and in the fourth by the natural crevices at points of the cortical cell junctions. It is concluded that the different frequencies of the four types of penetration observed after inoculation with isolates of the three IS group should be carefully explained in term of their different pathogenic and saprobic capabilities on pine.