A new technique for inoculation of conifer seedling roots with the laminated root rot pathogen, Phellinus weirii

Abstract

The efficacy of a novel inoculation technique for infecting conifer seedling roots with Phellinus weirii was demonstrated, Inoculum units were prepared from P. weirii-colonized stem segments of red alder (Alnus rubra) and branch segments of Douglas-fir (Pseudotsuga menziesii). In one experiment, potted and outplanted seedlings of nine coniferous species of known susceptibility to P. weirii (Douglas-fir, grand fir, lodgepole pine, noble fir, Sitka spruce, western hemlock, western redcedar, western white pine, and yellow cedar) were inoculated using the novel inoculum units. For all nine species combined, transfer of ectotrophic P. weirii was greater for potted seedlings than for outplanted seedlings (93% vs. 48%). However, rates of endotrophic P. weirii infection were similar for potted and outplanted seedlings (81% and 77% respectively). Results of this experiment parallel reported species susceptibility to P. weirii. In a second experiment, rooted cuttings of English yew and Pacific yew, coniferous species of unknown susceptibility to P. weirii, were tested. Transfer of the fungus to rooted cuttings was good for Pacific yew (77%) and poor for English yew (29%). Mortality of rooted cuttings of yew showed a similar trend: 49% of Pacific yews with P. weirii successfully transferred to roots were killed by the fungus vs. no mortality in the English yews. This is the first study to document the relative susceptibility of Pacific yew and English yew to P. weirii. Use of the inoculation technique for older trees and other root disease fungi is discussed.