Black alder is an important forest−forming species in Poland. Its wood is decomposed by many species of fungi. Ganoderma lucidum (Curtis) P. Karst. is a species of Basidiomycetes which belongs to family Ganodermataceae, order Polyporales. This fungus causes white rot decay of wood in dead and sometimes living alder trees. G. lucidum has been under partial protection in Poland since 2014. It is also red−listed as a rare species (category R – taxa with small populations) on the ‘Red list of the macrofungi in Poland’. The fungus was cut out with a sizeable fragment of wood from the alder stump in Łuków Forest District (eastern Poland) and transported to the laboratory of the Department of Mycology and Forest Phytopathology, Warsaw University of Life Sciences−SGGW. Pure culture of G. lucidum mycelium was obtained from a fragment of fruitbody. The aim of this study was to investigate, through laboratory decay tests, the ability of G. lucidum to degrade alder wood. Sterilization of wood samples (30×20×20 mm) consisted of placing the material in an accelerator and irradiating it with high−energy electrons at a dose of 30 kGy at the Institute of Nuclear Chemistry and Technology in Warsaw. On the next day, wood samples were put into 200 ml flasks with mycelium of G. lucidum on agar−wort medium (2 samples per flask). The flasks were placed in a Heraeus BK 600 incubator for 180 days, with a constant temperature of 22°C and humidity of 80 ±5%. Every 30 days 10 flasks were randomly selected, i.e. 20 samples of alder wood from this experiment. After each incubation period the samples were removed from the flasks, cleaned to remove mycelia and dried at a temperature of 105°C until they reached constant weight. By comparing mass of the samples at the start and the end of experiment in an absolutely dry state, the relative wood mass loss was calculated. After exposure times 180 days, the relative weight loss of alder wood as a result of decay by G. lucidum mycelium was on average 10.88%. The rate of the decay was almost constant during the study period. On some alder wood samples structures resembling fruitbodies of G. lucidum were noticed.
The paper reports the laboratory research on the natural wood resistance against white pattern fungal wood decomposition. Wood samples of 25, both European and exotic, tree species were collected and used (tab. 1). All samples were dried and weighted, then put on the mycelium of four different white rot causing fungi species: Fomes fomentarius ((L.: Fr.) Kickx), Schizophyllum commune (Fr.: Fr.), Stereum hirsutum ((Willd.: Fr.) Gray) and Trametes versicolor ((L.: Fr.) Pilát). After 30, 60 and 90 days of exposition the samples were put out, cleaned, dried and weighted again. The weight loss indicated the range of wood decomposition and allowed to estimate its natural resistance against fungal wood decay. The results showed that in laboratory conditions the range of all fungi species trophic abilities were much wider than the one observed in nature. Examined fungi were able to destroy wood from trees they never occur on. The reasons of this could be both mechanical (the absence of bark – natural barrier for fungi) and chemical (the less of chemical substances occurring in wood of living trees that could be responsible for its natural resistance against fungi).