In order to establish an optimal cryopreservation method, strains of Basidiomycete and Ascomycete fungi, which are among the most frequently used for wood durability testing, were evaluated using three cryopreservation procedures at -80°C. The main objective was to prevent decrease of the fungal virulence that may occur due to repeated routine sub-culturing procedures and to optimize the reactivation percentage of the strains, which is a particularly challenging issue in the case of Basidiomycetes fungi. In addition, the influence of the quality of water used for the preparation of the culturing malt agar medium on the mycelium growth and on the virulence of fungal strains was assessed. The vitality of all fungi was successfully preserved with cryopreservation at -80 °C during six months in sterile water with 25% or 50% of glycerol used as cryoprotectant. These two cryopreservation techniques negatively influenced the wood degrading ability of five Basidiomycete strains (out of the nine studied) that were tested for virulence after reactivation. Our findings suggest that the tested cryopreservation protocols are not suitable for long-term preservation of all Basidiomycetes species involved in standardized durability testing. However, they were found suitable for the tested strains of Rhodonia placenta, Coniophora olivacea and Trametes versicolor, which are commonly used in standardized efficacy tests. No general pattern was found regarding the optimal type of water, among the three types tested, used for the preparation of the fungal culture medium. The growth rates and virulence measured by mass loss of small-size wooden blocks varied between the strains exposed to the same culturing conditions. These results demonstrate the importance of species-specific optimization of laboratory culture conditions and maintenance procedures with regard to the fungal strains used.

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