Physiological specialization of Heterobasidion annosum on conifer hosts

Abstract

Eight conifer hosts belonging to five conifer species were inoculated in vitro with conidial suspensions of eight isolates of Heterobasidion annosum from Washington and California. The conifer trees were represented in inoculation tests by 1 cm diameter branch disks of 0.7 cm thickness. The ability of H. annosum to colonize dying woody tissue was assessed in terms of the number of conidiophores produced on the disks, measured 2 to 3 weeks after inoculation. Analysis of variance showed that there was a great range in conidiophore production with most of this variation attributable to host differences rather than to differences between the pathogen isolates. A second analysis involving four Tsuga heterophylla trees and five isolates showed similar results. In both the interspecific analysis with eight trees and the intraspecific analysis with four T. heterophylla trees, there were significant differential interactions between the isolates and the trees. This indicated that physiological specialization exists in this natural disease system at both the host-interspecific and host-intraspecific levels.