Abstract
Forty‐eight species of wood‐destroying basidiomycetous fungi which are represented by 74 strains were examined for their dependence on exogenous vitamin sources such as thiamine and biotin. In a series of up to 11 consecutive transfers to vitamin‐free glucose‐salt medium batches in a 4‐week rhythm it was shown that (i) the level of vitamin heterotrophy did not depend on whether the fungus was a parasite or a saprophyte, (ii) among both parasites and saprophytes vitamin‐independent and highly vitamin‐dependent isolates could be detected, (iii) almost 70% of the brown‐fungi, but only 30% of the white‐rot fungi dependend comparatively little on exogenous vitamin sources, (iv) the degree of vitamin heterotrophy varied in part dramatically among several strains of a given fungal species, (v) under permanent vitamin starvation none of the 74 fungal strains completely ceased growing, but several strains suffered an irreversible physiological collapse whose nature is still unknown. It is concluded that on natural timber resources both vitamin‐dependent and vitamin‐independent fungal strains can probably develop their normal pathovirulence and kratovirulence properties. Under conditions of vitamin starvation the equilibrium between the vitamin‐dependent decay fungus and the vitamin‐independent competitor may nevertheless become disturbed.