In Vitro Response of Heterobasidion annosum to Manganese’

. ABSTRACT Manganese (Mn) is postulated to play a role in wood decay caused by certain basidiomycetes. We determined the in vitro response of Heterobasidion annosum (Fr.) Bref. to Mn and compared differences between three isolates each of the S and the P intersterility groups from the Western United States. On manganese-amended malt agar plates, H. annosum produced a brownish-black pigment that increased with increasing concentration of Mn (1, 5, and 10 mM). The amount of pigment production varied among the isolates, but isolates of the S group clearly produced more pigment than those of the P group. In pigmented areas, hyphae appeared to be packed with black granules, and brownish-black granules/crystals were present in the medium. The black pigment implicates the presence of MnO, potentially resulting from the activity of Mndependent peroxidase (MnP). An assay for MnP did not detect the enzyme in crude culture filtrates of a chemically defmed, nitrogen-limited, buffered medium of the six isolates. The differential response of S and P group isolates to Mn raises questions about a role for this transition metal in H. annosum physiology.