Growth rate of Heterobasidion annosum in Picea abies established on forest land and arable land

The growth rates of Heterobasidion annosum in Norway spruce were investigated in southern Sweden. In one study, stump and tree roots in stands established on previous forest or arable land were inoculated with H. annosum-infested sawdust. After 1-3 yrs, the linear extent of colonization by the fungus was measured, based on detection of its conidiophores on incubated samples. The average growth rate was 25 cm yr(-1) in stump roots and 9 cm yr(-1) in tree roots, neither of which differed significantly between forest and arable land. The felling of a decayed tree could enhance the spread of H. annosum within root systems. in the second study, the height of discoloration and extent of colonization by H. annosum, measured as above. were assessed in naturally infected trees. On average, discoloration moved through the roots and stem at a rate of 36 cm yr(-1). Heterobasidion annosum was found 60 cm in advance of the discoloration, corresponding to a growth rate of 52 cm yr(-1).