Intraspecific variability in growth response to cadmium of the wood-rotting fungus Piptoporus betulinus

The intraspecific variability in growth response to cadmium (Cd) on agar media and in liquid culture was studied among fourteen strains of a wood-rotting fungus Piptoporus betulinus. The variability of Cd tolerance was found to be very high. The ED50 ranged from 6.8 muM Cd in the most sensitive strain, up to 255.1 muM in the most resistant one. On agar media the addition of Cd to nutrient media resulted in reduction of relative growth rate and increased lag time. While the reduction of growth rate was already apparent at 10 muM Cd, the lag time was significantly increased in higher Cd concentrations. Five strains of P. betulinus failed to grow at 250 muM Cd and none grew at 500 muM metal. Biomass production in liquid culture was less sensitive to addition of Cd than the growth rate on solid media. At 100 muM Cd the radial growth rate of the mycelium was reduced to 27%, whereas the dry mass of mycelium was 77% of the respective control value. A group of four Cd-sensitive strains was found, showing low metal tolerance both on solid media and in liquid cultures. Although the isolates originated from sites with different Cd-pollution level, no correlation between level of Cd-pollution and resistance (ED50) was found. The growth rate of fourteen tested strains displayed lower variability than biomass production, showing that radial growth rate is more species-specific and therefore more valuable for interspecific comparisons of growth response.