Effects of Scots pine (Pinus sylvestris) natural selection in old foci of Heterobasidion annosum root rot

Heterobasidion annosum (Fr.) Bref. is a fungal pathogen causing root rot – one of the most economically important diseases in coniferous stands in Europe, Asia and North America. A major objective of this study was to determine if the offspring of self-sown trees from natural regeneration in old foci of root rot is more resistant to infection by this pathogen than the offspring of plus trees. In experiments conducted in the greenhouse above 700 seedlings grown from seeds collected from 60 trees in 6 old foci of the disease (research plots) and 480 seedlings grown from seeds collected in 4 seed orchards were used. The pathogen was represented by 7 different fungal strains. Plus trees, whose grafts are used to establish seed orchards, were the selected elite of forest trees, but their offspring after inoculation with H. annosum had significantly worse results than the seedlings developed from the seeds collected in old foci of the disease (research plots). The greatest differences were observed in seedling dry weight. In inoculated seedlings from seed orchards it was 14% lower than in the control, while the dry weight of inoculated seedlings from research plots did not differ significantly from that of non-inoculated seedlings.