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

The efficacy of a novel inoculation technique for infecting conifer seedlin g roots with Phellinus weirii was demonstrated. Inoculum units were prepare d from P. weirii-colonized stem segments of red alder (Alnus rubra) and bra nch segments of Douglas-fir (Pseudotsuga menziesii), In one experiment pott ed and outplanted seedlings of nine coniferous spec ies of known susceptibi lity to P, weirii (Douglas-fir, grand fir,lodgepole pine, noble fir, Sitka spruce, western hemlock, western redcedar, western white pine, and yellow c edar) were inoculated using the novel inoculum units. For all nine species combined, transfer of ectotrophic P, weirii was greater for potted seedling s than for outplanted seedlings (93% vs. 48%). However, rates of endotrophi c P. weirii infection were similar for potted and outplanted seedlings (81% and 77% respectively). Results of this experiment parallel reported specie s susceptibility to P, weirii. In a second experiment, rooted cuttings of E nglish 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 mortalit y in the English yews. This is the first study to document the relative sus ceptibility of Pacific yew and English yew to P., weirii. Use of the inocul ation technique for older trees and other root disease fungi is discussed.