Strains of Heterobasidion annosum belonging to the S and
P intersterility groups (IGs) were compared in respect of laccase activity
on
various substrates. Biomass production was significantly lower in P cultures
than in S cultures. By contrast, laccase activity, measured
in relation to growth rate, was significantly higher for the P strains
tested, compared with a similar number of S strains, particularly
in substrates, rich in carbohydrates as well as in inorganic and organic
nitrogen. Using the Bradford assay method, P cultures were
shown to contain significantly higher amounts of protein than S. The pH
optimum of laccase for both IGs was 4·5 with guaiacol as
substrate and 5·3 with syringaldazine. Isozyme patterns varied greatly,
depending on strain, substrate and incubation time. In P
cultures 4–5 bands were obtained, whereas S strain laccase was mostly
separated into 2–3 isozyme bands. Only one was
significantly different in position between the IGs. The results may help
to explain why P strains are more aggressive than S strains
as pathogens and wood decayers.