Search

A parallel investigation to characterize host reactions involved in wound repair following abiotic injury and challenge with Armillaria ostoyae in three conifer species (Douglas-fir, western hemlock and western redcedar) was conducted in the southern Interior of British Columbia. In this study, we characterize wound healing in roots following freezing injuries to the bark. Five weeks following wounding, all conifers developed lignified impervious tissue (IT) around killed tissue, and a necrophylactic periderm (NP) formed internally abutting IT, although IT was difficult to discern in western redcedar. Phellogen restoration in the secondary phloem of some western hemlock roots was retarded around large clusters of sclereids. Displacement of phloem fibre cells occurred in western redcedar but did not appear to delay NP formation. In roots exhibiting expansion of necrosis to the vascular cambium, callus tissue was evident at the margin of the wound. Novel host reactions in western redcedar involving induced rhytidome formation and the formation of traumatic phloem resin ducts are described. [ABSTRACT FROM AUTHOR]

Structural responses in the bark and wood were described following penetration by Armillaria ostoyae in the roots of 20- to 30-year-old Douglas-fir, western hemlock and western redcedar trees. Tissue necrosis presumably caused by fungal exudates was commonly observed at inoculum contact. In Douglas-fir and western hemlock, A. ostoyae interfered with the initiation of active defence mechanisms involving the development of a lignified zone of impervious tissue (IT), necrophylactic periderm (NP) formation and compartmentalization of infected woody tissue. Breaching of IT and NP barriers was frequent, particularly around the clusters of sclereid cells in western hemlock. In western redcedar, the IT zone was inconspicuous. Induced rhytidome formation occurred in western redcedar either simultaneously with or after completion of NP development. The formation of this tissue facilitated en masse sloughing of infected tissue from the surface of roots. In western redcedar, traumatic phloem resin ducts formed in tangential bands surrounding the margin of expanded lesions. Effective compartmentalization in western redcedar was achieved by a barrier zone comprised of a higher-than-average number of axial parenchyma that accumulated polyphenolic deposits. A combination of host-mediated defence mechanisms in western redcedar resulted in a significantly higher frequency of effective resistance reactions than in western hemlock or Douglas-fir. [ABSTRACT FROM AUTHOR]