The research was carried out in plastic tunnels of the Laboratory of the Field Section of Seed Science, Nursery Economy and Selection of Forest Trees of the Agricultural Academy of Cracow in Krynica-Kopciowa. The intensity of after-sprouting damping-off of the silver spruce and common beech seedlings grown on the fresh sawdust-peat substrate and being in use since 2, 5, and 9 years. The mixing ratio of fir-spruce sawdust with moor peat was 1:1. The intensity of fir seedling damping-off was clearly lower (from 2% to 6%) than beech seedlings (from 5% to 14%). Seedlings of both tree species studied grown on fresh substrate were characteristic for their better health if compared with their growing on substrates of multi-year use. However no clear tendency was found for increasing intensity of damping-off along the incerasing time span of substrate use. The Fusarium oxysporum fungus was the most frequent factor of fir and beech seedling damping-off. Using the method of biotic series it was demonstrated that this pathogen did not encounter a biotic resistance from association of saprophytic fungi colonising substrates under study. Fungi refraining its increase occurred relatively most often in sawdust (fresh substrate component) while they were represented clearly less frequently in the substrate used for 2, 5, and 9 years. The results of the research carried out suggest that at the conditions of the Field Laboratory at Krynica-Kopciowa the sawdust-peat substrates used multiple times can be utilised at the culture of silver fir seedlings, but they should not be used for growing seedlings of common beech or the culture should be preceded with the disinfection of substrates. Utilising of sawdust-peat substrates seems to be more favourable for the production of seedlings in cycles longer than one year, because this limits multiplication of damping-off fungi on the substrate setting in this way more favourable phytosanitary conditions for the seedlings.
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