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Armillaria Root Rot in Eucalypt Forests: Aggravated Endemic Disease

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Title:Armillaria Root Rot in Eucalypt Forests: Aggravated Endemic Disease
Authors:Kile, G.A.
Date Issued:Oct 1983
Publisher:University of Hawai'i Press
Citation:Kile GA. 1983. Armillaria root rot in eucalypt forests: aggravated endemic disease. Pac Sci 37(4): 459-464.
Abstract:Species of the woody root rot fungus Armillaria are indigenous
in cool temperate rain forest, mixed forest, and wet and dry sclerophyll
eucalypt forests in Australia. Four species have been described or identified
from southeastern Australia: A. luteobubalina Watling and Kile, A. fumosa
Kile and Watling, A. hinnulea Kile and Watling, and A. novae-zelandiae
(Stevenson) Boesewinkel. The latter species was first described from New
Zealand, and A. hinnulea also occurs in that country. Armillaria novae-zelandiae
and A. hinnulea occur in wet forests (rain forest, mixed forest, and wet sclerophyll
communities), while A. luteobubalina and A. fumosa are found mainly in
dry sclerophyll forests.
Armillaria luteobubalina is so far the only species known to behave as a
primary pathogen in native forests. While the fungus has an extensive geographical
distribution in southeastern Australia, damage is most severe in
selectively logged forests in the central highlands of Victoria, where it is
estimated that approximately 3-5% of the forest area is moderately to severely
affect~. The fungus kills all species of eucalypts and a wide range of the under-
story trees and shrubs present in the forests. Most infections occur in small
(0.1-1.0 ha), well-defined patches, but larger (up to 20-30 ha), more diffuse
infections also occur. Evidence of primary pathogenicity includes (a) constant
association of the fungus with disease; (b) the pattern of disease development
within stands (the fungus spreads by root contact from infected food bases);
(c) correlation between root infection and symptom development in large trees;
(d) evidence of host resistance to infection; and (e) pathogenicity in pot and
field trials. There is no evidence that climatic stress or other pests or pathogens
initiate disease.
Within the forest, the fungus has a discontinuous distribution. Studies of
genotypes of the fungus (identified by analyses of mating alleles, since Armillaria
sp. are bifactorial heterothallic, or intraspecific antagonism), suggest that A.
luteobubalina consists of a community of genetically distinct mycelia. Individual
genotypes may contract, expand, or coalesce, depending on circumstance. The
development and status of the community depends on the two processes of
new basidiospore infection and local spread by vegetative growth through root
systems. Similar patterns of genotype distribution and clonal development were
evident in logged and unlogged forest. It is concluded that root rot caused by
the fungus is endemic in these forests but that logging has aggravated the disease.
Appears in Collections: Pacific Science Volume 37, Number 4, 1983

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