| Summary: | Host response to Armillaria ostoyae infection in western larch and Douglas-fir was studied
at the macroscopic, microscopic and biochemical level.
Examination of lesions resulting from natural infection and inoculation on the roots of 6-85
year old trees showed the events leading to lesion formation on both species of trees was
essentially the same. Resinosis and necrophylactic periderm (NP) formation in the roots of
trees less than about 10-years-old does not appear to be capable of halting the advance of
the fungus. In trees older than about 15 years the infection may become confined, by NP
formation, to a lesion in the bark, or by compartmentalization, to woody tissues present at
the time of infection. In 18-year-old western larch, NP's with multiple bands of phellem
may form around lesions. In many cases these NP's were associated with confined
infection. In Douglas-fir trees this response appears to occur between 25 and 35 years of
age.
Microscopic investigation of wound repair and natural infections on the roots of 10-11- and
25-27-year-old trees, using cryofixation and histology, revealed that the sequence of events
and the time involved in wound repair and phellogen renewal was very similar for both
species. However, none of the NP's in the infected samples from 11- or 25-year-old
Douglas-fir trees were successful in preventing the advance of A. ostoyae. In infected
samples collected from the roots of 10- and 27-year-old western larch trees, 68% and 45%
respectively had formed NP's which the fungus had not breached. NP's in normal healthy
tissues had bands of thin walled phellem (Pe) 1-4 cells wide. NP's formed in response to
wounding had bands of Pe 10-15 cells wide and NP's formed in response to infection had
bands of Pe up to 25 cells wide.
In the roots of both western larch and Douglas-fir, total protein concentrations in infected
and browned bark tissues were significantly lower than levels in adjacent, healthy and
wounded bark tissues sampled in spring, summer, autumn and winter. Separation of
proteins using SDS-PAGE revealed qualitative and quantitative differences in protein
profiles between healthy, adjacent and infected root bark samples from both western larch
and Douglas-fir trees. In western larch, most of the observed changes may have been
associated with physiological changes associated with seasonal variation. However, a 29.3
kDa protein, found in large quantities in the adjacent bark tissues from infected roots of
both 11- and 25-year-old Douglas-fir trees, was found to have significant (P=0.013)
homology with a chitinase associated with anti-fungal activity in herbaceous plants. === Forestry, Faculty of === Graduate
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