| Abstract: | In certain indigenous Picea abies Karst. stands in the Thuringian Forest (Middle-Europe), the incidence of butt rot and die-back of saplings caused by Armillaria mellea (Vahl ex Fr.) Karst. is conspicuously low in spite of a general spread of this fungus on stumps of clear-fellings. The majority of 43 isolates of A. mellea recovered from 13 highland infection centres were unable to form the brown type of rhizo-morphs (BR) in soil but could form the white type rhizomorphs (WR) on sterile substrates. In contrast, 17 isolates from lowland hardwood stands of average disease incidence produced both types of rhizo-morphs on both substrates. Results of inoculation of excised stem and root sections of Picea abies and Fagus sylvatica L. and saplings of P. abies associated with soils of different fertility levels indicated that the low disease index of certain P. abies stands is caused by the dominance of low-pathogenicity strains of A. mellea which lack the ability to form BR and penetrate non-injured bark of roots. Moreover, the poor podzolic highland soil types may contribute more to increase the survival rate and resistance of transplanted P. abies saplings than to reduce the spread of A. mellea. |
