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Wood Decaying Fungi

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Wood decay by fungi is typically classified into three types: soft rot, brown rot and white rot. The wood decayed by brown rot fungi is typically brown and crumbly and it is degraded via both non-enzymatic and enzymatic systems. A series of cellulolytic enzymes are employed in the degradation process by brown rot fungi, but no lignin degrading enzymes are typically involved. White rot fungi are typically associated with hardwood decay and their wood decay patterns can take on different forms. White rotted wood normally has a bleached appearance and this may either occur uniformly, leaving the wood a spongy or stringy mass, or it may appear as a selective decay or a pocket rot. White rot fungi possess both cellulolytic and lignin degrading enzymes and these fungi therefore have the potential to degrade the entirety of the wood structure under the correct environmental conditions. Soft rot fungi typically attack higher moisture, and lower lignin content wood and can create unique cavities in the wood cell wall. Less is known about the soft rot degradative enzyme systems, but their degradative mechanisms are reviewed along with the degradative enzymatic and nonenzymatic systems known to exist in the brown rot and white rot fungi. As we learn more about the non-enzymatic systems involved in both brown and white rot degradative systems, it changes our perspective on the role of enzymes in the decay process. This in turn is affecting the way we think about controlling decay in wood preservation and wood protection schemes, as well as how we may apply fungal decay mechanisms in bio-industrial processes.
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Wood decay by fungi is typically classified into three types: soft rot, brown rot and white rot.
The wood decayed by brown rot fungi is typically brown and crumbly and it is degraded via
both non-enzymatic and enzymatic systems. A series of cellulolytic enzymes are employed in
the degradation process by brown rot fungi, but no lignin degrading enzymes are typically
involved. White rot fungi are typically associated with hardwood decay and their wood decay
patterns can take on different forms. White rotted wood normally has a bleached appearance
and this may either occur uniformly, leaving the wood a spongy or stringy mass, or it may
appear as a selective decay or a pocket rot. White rot fungi possess both cellulolytic and
lignin degrading enzymes and these fungi therefore have the potential to degrade the entirety
of the wood structure under the correct environmental conditions. Soft rot fungi typically
attack higher moisture, and lower lignin content wood and can create unique cavities in the
wood cell wall. Less is known about the soft rot degradative enzyme systems, but their
degradative mechanisms are reviewed along with the degradative enzymatic and non-
enzymatic systems known to exist in the brown rot and white rot fungi. As we learn more
about the non-enzymatic systems involved in both brown and white rot degradative systems,
it changes our perspective on the role of enzymes in the decay process. This in turn is
affecting the way we think about controlling decay in wood preservation and wood protection
schemes, as well as how we may apply fungal decay mechanisms in bio-industrial processes.
:RRG'HFD
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Ϯ
CONTENTS
S.No. Chapters Page No
1. Introduction 3 to 8
2. Importance of Wood Decaying Fungi 9 to 10
3. Classification of Wood Decaying
Fungi
11 to 27
4. Control and Management of Wood-
destroying Fungi
28 to 45
5.
6.
Wood-Staining Fungi
References
46 to 54
55 to 66
ϯ
Chapter: 1
INTRODUCTION
Fungi which grow on wood are sometimes called "lignicolous" fungi. But
why develop a set of keys limited to fungi utilizing wood as a substrate? After all,
being lignicolous does not define a taxonomic category. Lignicolous fungi include
Ascomycetes and basidiomycetes and a large number of classes and orders within
each of these groups. Most of these taxa include both lignicolous and terrestrial
species. Rather than taxonomy, the keys focus on the biological activity holding
this otherwise disparate group of fungi together: their ability to degrade cellulose
and lignin, the major components of wood. This ability is often judged negatively
on our part. In fact, the introduction to Illustrated Genera of Wood Decay Fungi by
Dr. Fergus states that "This manual has therefore been prepared with the hope that
it will fill a definite need, that of the general forester to identify decay fungi. It will
also provide an illustrated Key for use in a Forest Pathology Laboratory course."
Dr. Fergus indicates that the keys in his manual were based on those used by Dr.
L.O. Overholts for use in a course in Forest Pathology. Dr. Fergus' book begins to
answer the question posed earlier. One reason you might want a set of keys to
wood decay fungi is because these fungi cause economic loss. Forest trees and
valuable landscape trees can be infected and rotted by these fungi. Knowing the
species growing on a tree can help the forester determine the likely extent of loss.
Different species are associated with different amounts of decay in the tree.
Additionally, some species are restricted to sapwood and will not affect the
merchantable volume of heartwood. Some fungi can decay sound wood; others
decay only decaying wood and bark.
Every year an enormous amount of wood and wood products are destroyed
by decay, rot and decomposition. Decomposition refers to the process by which
ϰ
tissues of dead organisms break down into simpler forms of matter. Such a
breakdown is essential for new growth and development, because it is the basis for
recycling limited chemical compounds, as well as freeing up limited physical space
in the environment. Fungi are the main organisms responsible for wood decay. A
wide range of fungi occur on wood using various constituents for their metabolism.
This article is a general overview of the fungi, primarily basidiomycetes, involved
in wood decay as it relates to structural integrity of building materials, buildings,
milled wood and wood products.
Decay fungi need oxygen, water and a food source to exist. Wood as a food
source is limited to those fungi which are able to utilize the components and in the
process break down the wood. Since wood and wood products are used in
construction of commercial and residential buildings, the key to longer lasting
wood structures and products is to keep the wood dry. Dry wood will not decay. If
you add water to dry wood, the cell walls absorb water up to a moisture content of
about 28%. Above that, the wood reaches the fiber saturation point and free water
becomes available. Decay fungi require free water so the moisture content of wood
must be above 28% to decay. For practical purposes, a value of 20% is used as a
cutoff, leaving a margin of error for avoidance of decay. Fungi have an external
method for breaking down their food by secreting digestive enzymes and other
chemicals into the substrate where they are growing. This enables the fungi to then
absorb predigested food products. This external digestion process requires that
liquid water be present so the enzymes can be secreted and then the useable food
products can diffuse back into the fungus. Without this moisture, the fungus cannot
be active or grow. Without water, it may either become dormant or die.
Wood decay is generally classified into two main groups, white rots and
brown rots, based on the wood residue left behind following fungal digestion. Two
ϱ
other types include "dry rot", which is a form of brown rot caused by water-
conducting decay fungi, and "soft rot", referring to decay caused by certain
Ascomycetes and asexual fungi.
The main wood-inhabiting group of basidiomycetes is commonly known as
the polypores. It's estimated that in North America, no less than 100 species of
polypores cause decay in woody plants and timber, while approximately 75 species
are responsible for 90% of the important decays produced in timber and wood
products. Most polypores are saprophytic and utilize dead wood as their food
source. These fungi commonly appear as hard, tough, corky, leathery or woody
structures of various shapes and sizes (see figure 1). They have a fertile surface
(where spores are produced), usually made of pores or tubes closely packed
together. Polypores are mostly wood inhabiting fungi that are able to utilize
components of wood as their primary source of energy for growth and
reproduction. When a fruiting body is seen on wood, the mycelium, or main body
of the fungus, is usually not so visible, growing within the wood obtaining
nutrients from it.
Figure 1: Orange-brown polypore fungus (family Polyporaceae), with some leafy
("foliose") green lichen, on the trunk of a dead tree. Winter, Mine Falls Park,
Nashua, New Hampshire. Source: HikingWithChuck.com, used with permission
Copyright © 2008 by Charles J. Bonner, all rights reserved
ϲ
When fungi decay wood, the process involves breaking down complex
chemical compounds, primarily cellulose and/or lignin. Cellulose is a
polysaccharide composed of linear chains of glucose molecules. All plants have
this chemical compound as the primary cell wall component. Cellulose is the most
common organic compound on Earth and makes up roughly 50% of wood. Lignin
is a complex polymer of phenolic units and relatively resistant to decay. It plays a
key role in the carbon cycle as the most abundant aromatic compound in nature,
providing a protective matrix in the plant cell wall. This amorphous and insoluble
polymer is not susceptible to hydrolytic attack, in contrast to cellulose. Although
lignin is a formidable substrate, its degradation by certain fungi was recognized
and described nearly 125 years ago. These basidiomycetes are the only organisms
capable of efficient depolymerization and mineralization of lignin.
No information is available for health effects, toxicity, or allergenicity with
regards to these fungi. The actual damage that decay fungi cause in timber is
enormous yet difficult, if not impossible, to accurately determine. Each year a large
amount of timber is lost on account of decay fungi in forests as well as in and on
wood products and structural timbers.
Decay fungi of living trees can be categorized and named using a number of
different methods. Accurate identification provides valuable information about the
impact of decay on the tree, mode of action and importance to risk analysis. The
presence of any fruiting body on a tree requires that the tree be investigated more
closely for decay. Identification of the most common wood decaying fungi of
living trees includes the following key factors:
ϳ
¾ The Fungi That Cause Decay
Taxonomy/Classification
%DVLGLRP\FHWHV
$VFRP\FHWHV
The vast majority of common tree decay fungi are basidiomycetes.
¾ Name of Decay Based on Location
Note that each fungus is specific to the location on the tree where it is found.
x Root and Butt
Armillaria spp.
Grifola frondosa
Ganoderma lucidum
Inonotus dryadeus
Ustulina deusta
Xylaria polymorpha
x Trunk and Stem
Pleurotus ostreatus
Polyporus squamosis
Schizophyllum commune
Climacodon septentrionalis
Cerrena unicolor
Daedalea quercina
Phellinus robineae
Fomes fomentarius, Phellinus ignarius
Perenniporia fraxinophilia
ϴ
Common Sap rots
x Trunk and Butt
Laetioporus sulphureus
Ganoderma applanatum
¾ Types of Wood Decay
Type Agent Color Texture Chemistry
White
Rot
Basidiomycota ±bleached fibrous
Decays mostly lignin
and secondarily
cellulose.
Brown
Rot
Basidiomycota ± brown
fibrous texture
lost early,
cross-hecking
Decays mostly
cellulose and
secondarily lignin.
Great strength loss
occurs in initial stages
of decay.
Soft
Rot
Asco- and
Deuteromycota
bleached
or brown
usually on
surface, some
fibrous texture
lost, cross-
checking in
some cases
Carbohydrates
preferred, but some
lignin lost too
ϵ
Chapter: 2
IMPORTANCE OF WOOD DECAYING FUNGI
But being able to identify lignicolous fungi causing economic loss is only
one reason why keys to lignicolous fungi might be useful. In the material below, I
briefly describe other important reasons people have to know the species of fungi
which are found growing on wood. Wood decay fungi are the preeminent recyclers
of wood in ecosystems. Without these fungi, wood would never decay. We would
be "up to our eyeballs" in twigs, limbs, and tree trunks. Worse, the valuable
nutrients in this wood would be locked up and unavailable for new growth. The
species of fungi responsible for decaying the wood of the different species of
hardwood and softwood trees is of ecological interest. Wood decay fungi include
many sought-after edible species such as Pleurotus ostreatus, Grifola frondosa,
and Laetiporus sulphureus.
x Wood decay fungi are used as myco-medicinals. Preparations made from
species such as Ganoderma lucidum and Trametes versicolor are the
mycological equivalent of herbal medicinals.
x Wood decay fungi are screened for pharmaceutical and industrial
compounds.
x Wood decay fungi are favorite subjects for photographers and other artists.
x Wood decay fungi are used by hobbyists to dye wool and other
fabrics. Trametes suaveolens, for example, yields a much sought purple dye.
x Wood decay fungi are used by hobbyists to make paper. Many of the species
contain tough, fibrous cells which, when separated, can be fashioned into
ornamental paper products.
ϭϬ
x Wood decay fungi utilize different proportions of cellulose and lignin from
wood, leading to what is termed white rot or brown rot. This character is
sometimes given taxonomic importance. For example, most species now in
the genus Oligoporus were formally included in the
genus Tyromyces. Tyromyces, however, is now restricted to white rot species
and any brown rot species formally in it were transferred to the
genusOligoporus which is restricted to brown rot species. For
example, Oligoporus caesius was formally Tyromyces caesius.
x Wood decay fungi provide fascinating examples of biological relationships.
For example, Armillaria mellea is a much sought edible species. It is also
one of the few gilled mushrooms that is an important forest tree
parasite. Armillaria mellea is sometimes parasitized by another gilled
mushroom called Entoloma abortivum, or the Aborted Entoloma. A
parasitized Armillaria becomes a more or less solid mass of flesh and never
develops gills. The two species often grow near each other and for many
years it was thought that the aborted form was Entoloma parasitized
by Armillaria. It was only in recent years that the reverse was shown to be
true. To call Entoloma abortivum, the Aborted Entoloma, now makes little
sense but will the name change?
x Wood decay fungi provide subjects for student research projects. For
example, students at Messiah College have worked with me to study
relationships of wood decay fungi to plant species. This type of study
attempts to determine which wood decay fungi occur most commonly on
wood of a given species of tree. This sort of study not only requires the
identification of the fungus but also the identification of the wood, a
formidable task at times given that most of these fungi are found on dead
logs and stumps in various states of decay.
ϭϭ
Chapter: 3
CLASSIFICATION OF WOOD ROTTING FUNGI
Wood decay by fungi is typically classified into three types: soft rot, brown rot and
white rot. The wood decayed by brown rot fungi is typically brown and crumbly
and it is degraded via both non-enzymatic and enzymatic systems. A series of
cellulolytic enzymes are employed in the degradation process by brown rot fungi,
but no lignin degrading enzymes are typically involved. White rot fungi are
typically associated with hardwood decay and their wood decay patterns can take
on different forms. White rotted wood normally has a bleached appearance and
this may either occur uniformly, leaving the wood a spongy or stringy mass, or it
may appear as a selective decay or a pocket rot. White rot fungi possess both
cellulolytic and lignin degrading enzymes and these fungi therefore have the
potential to degrade the entirety of the wood structure under the correct
environmental conditions. Soft rot fungi typically attack higher moisture, and
lower lignin content wood and can create unique cavities in the wood cell wall.
Less is known about the soft rot degradative enzyme systems, but their degradative
mechanisms are reviewed along with the degradative enzymatic and non-
enzymatic systems known to exist in the brown rot and white rot fungi. As we
learn more about the non-enzymatic systems involved in both brown and white rot
degradative systems, it changes our perspective on the role of enzymes in the
decay process. This in turn is affecting the way we think about controlling decay
in wood preservation and wood protection schemes, as well as how we may apply
fungal decay mechanisms in bio-industrial processes.
In terms of both its physical and chemical properties, wood is an
exceptionally difficult substrate to degrade. One of the principal reasons is that
ϭϮ
wood contains very low levels of nitrogen, which is needed to produce the
enzymes that degrade the main structural polmers of wood - cellulose (about 40-
50% of the dry weight of wood), hemicelluloses (25-40%) and lignin (20-35%).
The lignin component also presents a barrier to wood decay because lignin is a
complex aromatic polymer that encrusts the cell walls, preventing access of
enzymes to the more easily degradable cellulose and hemicelluloses. In addition to
these points, wood often contains potentially fungitoxic compounds, which are
deposited in the heartwood. In broad-leaved trees the toxic compounds are
usually tannins, well known for their ability to cross-link proteins, making animal
skins resistant to decay. In contrast, conifers contain a range of phenolic
compounds such as terpenes, stilbenes, flavonoids and tropolones. The most toxic
of the tropolones are the thujaplicins which act as uncouplers of oxidative
phosphorylation; they are particularly abundant in cedarwood, making this a
naturally decay-resistant wood for high-quality garden furnishings, etc.
Despite this formidable list of obstacles, woody tissues are degraded by
fungi, and these wood-decay fungi falls into three types according to their mode of
attack on the woody cell walls - soft-rot fungi, brown-rot fungi and white-rot
fungi.
Soft-rot fungi
Soft-rot fungi grow on wood in damp environments. They are the
characteristic decay fungi of fence posts, telegraph poles, wooden window frames,
the timbers of cooling towers, and wood in estuarine or marine environments.
They have a relatively simple mode of attack on wood, illustrated in Fig. 2. Their
hyphae grow in the lumen of individual woody cells, usually after entering through
ϭϯ
DµSLW¶GHSUHVVLRQLQWKHZDOO7KHQWKH\SURGXFHILQHSHQHWUDWLRQEUDQFKHVWKDW
grow through the thin, lignin-coated S3 layer of the wall, to gain access to the
thick, cellulose-rich S2 layer. When the penetration hyphae find a longitudinal
plane of weakness in the S2 layer, they produce broader T-shaped hyphae which
grow along the plane of weakness and secrete cellulase enzymes. The diffusion of
these enzymes creates a characteristic pattern of decay, seen as rhomboidal
cavities within the cell wall. These persist even when the fungi have died, leaving
WKHFKDUDFWHULVWLFµVLJQDWXUH¶RIDVRIW-rot fungus. The soft-rot fungi have little or
no effect on lignin, which remains more or less intact. All the soft-rot fungi need
relatively high nitrogen levels for wood decay, typically about 1% nitrogen
content in the wood. If this is unavailable in the wood itself, then nitrogen can be
recruited from the environment, such as the soil at the bases of fence posts, etc.
Soft rot in wood often
appears brown and can
be confused with decay
caused by brown rot
fungi.
Soft rot is different from other
types of wood decay. Chains
of cavities are produced inside
the cell wall. This micrograph
taken of a section from soft-
rotted wood and viewed with a
light microscope shows
cavities within the cell walls.
ϭϰ
The fungi that cause soft rots include several Ascomycota and mitosporic
species, such as Chaetomium and Ceratocystis in terrestrial environments and
species of Lulworthia, Halosphaeria and Pleosporain marine and estuarine
environments.
Fig 2. (a) Diagram of the cell wall layers in woody tissue, showing the
arrangement of cellulose microfibrils. ML = middle lamella between adjacent
woody cells; P = thin primary wall with loosely and irregularly arranged
microfibrils; S1-S3 = secondary wall layers. (b) Characteristic decay pattern of a
soft-rot fungus in the S2 layer. The fungus penetrates by narrow hyphae, then
forms broader hyphae in planes of weakness in the wall, and these hyphae produce
rhomboidal cavities where the cellulose has been enzymatically degraded. [ Jim
Deacon]
ϭϱ
Brown-rot fungi
Brown-rot fungi are predominantly members of the Basidiomycota,
including common species such as Schizophyllum commune, Fomes
fomentarius WKH µKRRI IXQJXV¶ of Scottish birch woods DQG WKH µGU\-rot
IXQJXV¶ Serpula lacrymans. Many of the brown-rot fungi produce bracket-shaped
fruitbodies on the trunks of dead trees, but the characteristic feature of these fungi
is that the decaying wood is brown and shows brick-like cracking ± a result of the
uneven pattern of decay, causing the wood to split along lines of weakness (See
Fig. 3 7KH WHUP µEURZQ URW¶ UHIHUV WR WKH FKDUDFWHULVWLF FRORXU RI WKH GHFD\HG
wood, because most of the cellulose and hemicelluloses are degraded, leaving the
lignin more or less intact as a brown, chemically modified framework.
Fig 3. Part of a pine stump showing the characteristic brick-like decay by brown-
rot fungi. [ Jim Deacon]
The hyphae of brown-rot fungi occur very sparsely in the wood, often
ϭϲ
restricted to the lumen of woody cells, and yet they cause a generalized decay in
which the S2 wall layer is almost completely degraded. This type of decay cannot
be explained by the diffusion of cellulase enzymes, which are too large to diffuse
very far, and too large even to pass through the pores in the S3 layer. In fact, the
cellulases of brown-rot fungi have little effect on cellulose in vitro, unlike the
cellulases of soft-rot fungi. Instead, the brown-rot fungi degrade cellulose by
an oxidative process, involving the production of hydrogen peroxide during the
breakdown of hemicelluloses. Being a small molecule, H
2
O
2
can diffuse through
the woody cell walls to cause a generalized decay. In support of this, the
characteristic decay pattern of brown-rot fungi can be mimicked experimentally by
treating wood with H
2
O
2
alone, and at least one of these fungi, Poria placenta,has
been shown to degrade cellulose only if hemicelluloses also are present, as
substrates for generating H
2
O
2
. This mode of attack is an efficient way of using the
scarce nitrogen resources in wood, because it does not require the release of large
amounts of extracellular enzymes.
ϭϳ
An urban tree with brown
rot. The large branch
failed and broke off due
to the presence of decay.
Brown rot has little
structural integrity and
large losses of wood
strength occur early in the
decay process. Urban
trees with decay can be
very hazardous.
Acloserviewofbrown-
rooted wood is shown in
this photo. In advanced
stages of decay the wood
cracks and checks into
cubicle pieces. Little to
no integrity remains in
this decayed wood.
Scanning electron
micrograph of brown-
rotted wood. Only slight
pressure causes the wood
cell walls to crumble into
minute fragments.
White-rot fungi
White-rot fungi are more numerous than brown-rot fungi. They include
both Ascomycota, such as Xylaria spp. (Fig. 4), and Basidiomycota
(e.g. Armillariella mellea).
ϭϴ
Fig 4. Upper row: Two common Ascomycota that cause white rots. Left: Xylaria
hypoxylonWKHµFDQGOHVQXII¶IXQJXVRIWHQVHHQRQ rotting stumps. The upper parts
of the fork-shaped structures are covered with white, powdery
conidia. Right: Xylaria polymorpha µGHDG PDQ¶V ILQJHUV¶ ZKLFK RIWHQ JURZV
from the bases of rotting wood stumps. Bottom: A section cut through one of the
³GHDG PDQ¶VILQJHUV´VKRZLQJQXPHURXVSHULWKHFLDMXVWEHORZWKHVXUIDFHRIWKH
fruitbody.
Fig 4. Small, leathery, bracket-shaped fruitbodies of the white-rot fungus Coriolus
versicolor, growing in an unexpected setting ± is nothing sacred!?
ϭϵ
The white-rot fungi seem to use conventional cellulase enzymes for wood
decay, but they are extremely efficient in their use of nitrogen. For example, the
nitrogen content of Coriolus versicolor is about 4% when the fungus is grown on
laboratory media of Carbon-to-nitrogen ratio, 32:1, but only 0.2% when grown on
a medium of C:N, 1600:1. In nitrogen-poor conditions this fungus seems
preferentially to allocate nitrogen to the production of extracellular enzymes and
essential cell components, and it also efficiently recycles the nitrogen in its
mycelia. White-rot fungi might also benefit from the growth of nitrogen-fixing
bacteria in wood.
ϮϬ
Cross section of an oak
tree with white rot. The
fungus has decayed the
sapwood and dark
heartwood turning it
white. This white rot
fungus attacked all cell
wall components.
Scanning electron
micrograph showing the
hypha of a white rot fungus
in the cell lumen of a wood
cell. Extracellular enzymes
are degrading all of the cell
wall components
simultaneously causing
erosion troughs to form in
the cell wall
A cross section of wood
with white rot showing
the fungus has degraded
some cells completely
but not others.
The most remarkable feature of white-rot fungi is their ability completely to
degrade lignin ± they are the only organisms known to do this. As shown in Fig.
11.22, lignin is a complex polymer composed of three types of phenyl-propane
unit (six-carbon rings with three-carbon side chains) bonded to one another in at
least 12 different ways. If lignin were to be degraded by conventional means it
Ϯϭ
would require a multitude of enzymes. Instead, lignin is degraded by an oxidative
process. The details of this are complex, but essentially the white-rot fungi
produce only a few enzymes (lignin peroxidase, manganese peroxidase, H
2
O
2
-
generating enzymes, and laccase) and these generate strong oxidants, which
YLUWXDOO\³FRPEXVW´WKHOLJQLQIUDPHZRUN(Kirk & Farrell, 1987).
A split section of a
pine tree with white-
pocket rot caused
by Phellinus pini.The
white areas are
delignified zones
where the fungus has
removed lignin but not
the cellulose. White-
pocket rot fungi cause
a selective attack on
lignin and
hemicellulose in
wood.
A mottled white rot in wood
decayed by Ganoderma
applanatum. This fungus
causes a combination o
f
delignification and a
simultaneous white rot attack
in the wood. White areas with
black spots containing
manganese (deposited by the
fungus) are delignified while
the tan areas have a
simultaneous white rot. In the
tan areas large degraded
zones form and these holes
fill with white mycelium o
f
the fungus.
A cross section of wood
from a white-pocket
area of decayed wood
showing delignified
wood cells. These cells
have no middle lamella
(this is the area between
cells that has high
lignin concentration).
Only the cellulose-rich
secondary walls remain
after advanced decay.
ϮϮ
The major enzyme that initiates ring-cleavage is laccase, which catalyses
the addition of a second hydroxyl group to phenolic compounds. The ring can then
be opened between two adjacent carbon atoms that bear the hydroxyl groups. This
process occurs while the ring is still attached to the lignin molecule. It is
termed ortho fission, in contrast to meta fission which bacteria employ to cleave
the phenolic rings of pesticide molecules (where the ring is opened at a different
position).
The other enzymes are involved mainly in generating or transferring
oxidants. They include glucose oxidase which generates H
2
O
2
from
glucose, manganese peroxidase which oxidises Mn (II) to Mn (III), and which
can then oxidise organic molecules, and lignin peroxidase which catalyses the
transfer of singlet oxygen from H
2
O
2
to aromatic rings and is one of the main
initiators of attack on the lignin framework. These initial oxidations involving
single electron transfers generate highly unstable conditions, setting off a chain of
chemical oxidations.
In addition to the fungi mentioned above, several others are commonly
found on stumps or on the decaying major roots of trees. Examples of these
include the distinctive Pholiota squarrosa, the very common "sulphur
tuft, Hypholoma fasciculare and the "Velvet shank", Flammulina velutipes.
Ϯϯ
COMMON ROOT- AND WOOD-ROTTING BASIDIOMYCOTA
The images below show three common root-rotting or stump-rotting fungi -
Pholiota squarrosa (the "Shaggy Parasol"), Hypholoma fasciculare (the "Sulfur
tuft") and Flammulina velutipes ("Velvet shank"). All three of these fungi are
commonly seen growing in dense clusters at the bases of older trees, or from
stump surfaces, or from just below ground level, where the clusters of fruiting
bodies can be seen to follow the lines of the older, radiating roots. These are
essentially saprotrophic fungi that progressively rot the older roots, but they
seldom cause significant damage to healthy trees.
Ϯϰ
Fig. 5. A cluster of young fruitbodies of Pholiota squarrosa, growing from the
base of an old ornamental cherry tree.
Fig. 6. A cluster of fruitbodies of Sulfur tuft (Hypholoma fasciculare) seen from
above, growing from the base of a tree stump. The conspicuous sulfur-yellow
colour of the cap gives rise to the common name, Sulfur tuft.
Ϯϱ
Fig. 7. Cluster of fruitbodies of H. fasciculare in side view. The gills are initially
yellow but eventually darken to purple-brown as the spores mature.
Fig. 8. A cluster of fruitbodies of Flammulina velutipes growing from the surface
of a cut tree stump. Also seen at lower left and right are the thin leathery brackets
Ϯϲ
of Coriolus versicolor growing from the same stump.
Fig. 9. A view of the underside of Flammulina velutipes, showing that the stipes
(stalks) of this toadstool have a dark, velvety appearance, characteristic of this
fungus.
A set of keys to fungi restricted to growing on wood eases the identification
process for people with all of the above interests. Field guides and technical
monographs cover all genera and species of a group. The identification process
can become tedious for groups with many terrestrial species or when using
comprehensive field guides. Furthermore, technical literature is often not available
to the general user as it may reside in obscure locations or it may require more
Ϯϳ
technical mycological "know how" than that possessed by the general user.
For any of the activities described above, it is my hope that these keys and
pictures, within their limitations, will be found useful to identify many of the fungi
found growing on wood.
Ϯϴ
Chapter: 4
CONTROL AND MANAGEMENT OF WOOD-DESTROYING
FUNGI
Inspection
The inspector may use the pick test to detect loss of wood toughness and the
presence of wood decay at as little as 5 to 10 percent loss of weight. In this test, a
sharp pointed object, such as an ice-pick, is used to poke into and pry up a segment
of ZRRG HVSHFLDOO\ WR ³ODWHZRRG´ DUHDV RI GDUNHU ULQJV ,Q GHFD\HG ZRRG WKH
pried-up section will break abruptly, directly over the tool, whereas in sound wood
the break will occur at a point away from the tool. This test is very subjective, but
it is possible to detect very early stages of decay by both brown rot and white rot.
The surface molds and stain fungi grow more rapidly than decay fungi and
often appear on wood during construction. Fungus growth will not continue after
construction if the wood dries out. However, the presence of stain fungi indicates
that conditions at one time were suitable for decay, and an inspection using a
moisture meter should be conducted to see if the wood is still moist enough to
support decay fungi.
Measuring wood moisture with a moisture meter is an important method to
determine:
_ Whether wood has a moisture content (20 percent or above) that will lead to
decay.
_ Small changes in the moisture content of wood to demonstrate the success of a
moisture control program over time.
_ The likelihood of infestation or reinfestation by wood-boring insects.
_ Whether fungi seen on the wood surface are still actively growing.
Ϯϵ
The electric resistance of wood decreases as its moisture content increases.
This is the basis for the operation of portable moisture meters. They measure the
resistance between two needles inserted into wood and give a direct readout of
moisture content. The higher the meter reading (decreasing electric resistance), the
higher the amount of moisture in the wood. Moisture meter readings can be
affected by the wood species involved, moisture distribution, grain direction,
chemicals in the wood, weather conditions, and temperature. Thus, directions and
information supplied with the meter must be understood and followed to ensure
accurate readings. Some common sources of moisture in structures are listed
below. These areas should be inspected for signs of wood-decaying fungi and
moisture above 20 percent.
_ Water vapors from the combustion of natural gas that improperly vent into the
attic or other enclosed areas.
_ Condensation on windows flowing down onto and into sills.
_ Moisture from crawl spaces and the dirt below (up to 100 pounds/day/1,000
square feet).
_ Absent or improperly placed drain pipes, downspouts, etc.
_ Leaking roofs.
_ Poor side wall construction.
_ Improperly sealed foundations, basement walls.
B'LUHFWFRQWDFWRIZRRGZLWKVRLORUFRQFUHWHDOORZLQJ³ZLFN´ DFWLRQWKDWSXOOV
water into wood.
_ Improper drainage of water away from structure or out of crawl spaces.
_ Improperly fitted flashings at roof lines or shingles with improper overhang.
_ Improper moisture barriers under stucco, shingles.
_ Sweating water pipes.
ϯϬ
_ Improper exterior grade that allows water to drain toward the structure and
remain in contact with it.
_ Dripping air conditioners or swamp coolers.
_ Leaking plumbing, appliances, toilets, shower stall pans.
_ Improper seals or caulk around bathtubs and showers.
_ Lack of vents or windows in bathrooms that allow moisture from baths and
showers to accumulate.
_ Plugged or leaking downspouts from roof gutters.
Condensation is free water or ice extracted from the atmosphere and
deposited on any cold surface. The term relative humidity is a means of
describing the amount of water vapor held by air. If more water vapor is injected
into air than the air can hold at that temperature, the
excess condenses into visible droplets.
In recent years, the shift in building practices to larger homes that are more
airtight has led to additional condensation problems. Energy conservation practices
have increased the air-tightness of buildings. Also, emphasis has been placed on
the installation of humidifiers in heating units to create a more comfortable
environment. They also increase the likelihood of moisture problems in wood.
Finally, improperly installed insulation may contribute to moisture problems.
There are numerous sources of water vapor in buildings. Mopping floors,
washing clothes, cooking, baking, and so forth introduce an estimated 1 pound of
water per day into the air of an average home. A poorly ventilated crawl space may
produce up to 100 pounds of water per day per 1,000 square feet. These moist
environments are favorable for the reproduction and survival of decay fungi,
termites, and other moisture-loving insects.
ϯϭ
Prevention
Simply maintaining a building properly by fixing leaky pipes and faucets,
repairing a leaky roof, etc., is often all that is needed to control wood-destroying
fungi. Simple repairs such as these will often save thousands of dollars by
preventing damage and expense from wood-destroying fungi. Prevention, however,
begins even before the maintenance stages²the structure must be built properly to
begin with.
When wood is used in the construction of a building, it should be well
seasoned so that it does not contain enough natural moisture to support decay
fungi. Wood should not be used in those parts of construction where it can be
moistened by wet soil. In extremely wet or humid areas, construction lumber is
frequently treated with preservative chemicals to prevent fungus damage.
Water should drain away from a properly constructed building. This is
accomplished through proper grading and roof overhang and the use of gutters,
downspouts, and drain tile. Proper grading should be taken care of before
construction; it is usually an expensive task if done later. The other methods should
be used to move water away from the foundation walls. It is important that
condensation (e.g., from air conditioners) be properly drained. Indoors,
dehumidifiers should be used where moisture in the air is likely to be a problem.
Proper ventilation in crawl spaces can be obtained by installing 1 square foot
of opening for each 25 linear feet of wall. These openings should be located so as
to provide cross-ventilation. This opening should be unobstructed. Where
screening, wire mesh, or louvers are used, the total opening should be greater than
1 square foot per 25 feet of wall. Provision should be made to close vents off
during the winter.
Attic vents are recommended at the rate of 1 square foot of vent for every
150 to 300 square feet of attic floor space. Vents should be located both near the
ϯϮ
ridge and at the eaves to induce airflow. Where louvered openings cannot be used,
globe ventilators, fan exhaust ventilators, or special flues incorporated in a
chimney may be best. Inlet openings under the cornice or roof overhang are
required in all cases. Flat roofs where the same framing is used for ceiling and roof
require openings between the joists. Any opening provided should be screened and
protected from the weather.
Vapor barriers are a preventive measure usually applied to the subareas of
buildings. Installation of a vapor barrier on the soil surface will cause soil moisture
to condense on the barrier and return to the soil rather than condense on the floor
and joists above. Covering the soil with roofing paper or 4-mil to 6-mil
polyethylene sheets can make adequate barriers. Proper installation of these
barriers is essential; a small portion of the soil surface should be left uncovered.
/HDYLQJVSDFHVEHWZHHQVWULSVIRUH[DPSOHDOORZVWKHVXEDUHDWR³EUHDWKH´EHWWHU
and any standing water will have a place to go. This is particularly important if the
subarea is very wet prior to installation. This will also allow wood in the crawl
space to dry slowly, minimizing warping and cracking. Inspection 1 to 3 weeks
after installation will allow for proper adjustments of the vapor barrier so that the
wood can slowly recover from excess moisture.
Preventive Measurements
x Water is the enemy of wood! Moisture control must be an integral part of
any plan designed for the prevention of wood decay fungi. The following
guidelines are a good way to start:
x Untreated wood should never be in contact with the ground. Posts, piers and
framing members should always be placed on concrete footers above the
surrounding soil level.
ϯϯ
x 9HQWLODWLRQLQFUDZOVSDFHVLVFULWLFDOWRSUHYHQW³GHDGDLU´VSDFHV$GHTXDWH
FURVV YHQWLODWLRQ EHQHDWK WKH VWUXFWXUH ZLOO PLQLPL]H ³GHDG DLU´ VSDFHV
Vents should be installed at a minimum of two square feet per openings for
every 25 linear feet of wall. Avoid any obstructions of the vents by
vegetation, storage or physically sealing off openings.
x In crawlspaces with continuously moist soil a vapor barrier can be installed
to minimize condensation onto framing components. Vapor barriers are
designed to maintain the moisture at the soil level.
x Use pressure treated wood, properly, or select heartwood (redwood, cedar) if
moisture conditions are unavoidable (decks, wood in ground contact, etc.).
x Wood may be protected from decay with a borate treatment by a licensed
professional.
x Repair plumbing leaks as soon as they are noticed.
x Rain gutters and downspouts should be cleared of debris. Roof leaks should
be fixed immediately.
x Maintain all exterior wood surfaces sealed with a water repellent paint or
stain.
x Maintain all interior wood window sills sealed with a water repellent paint
or stain, since condensation is common around windows
x Keep all commodes secured tightly to the floor to minimize possible leakage
at the seal.
x Periodic inspection should be part of a routine maintenance schedule.
Habitat Modification
The first step in correcting a fungus condition is to determine the source of
moisture and eliminate it, if possible. All badly rotted wood should be removed
ϯϰ
and replaced with sound, dry lumber. When it is not possible to eliminate the
source of moisture entirely, the replacement lumber should be pressure treated with
a wood preservative before installation. Wood should not be allowed to remain in
contact with the soil.
Chemical Control
In most cases, spraying chemicals will not control wood-decaying fungi.
Eliminating moisture sources and replacing decayed wood with pressure-treated
wood is the recommended control. Chemical use, however, may be warranted in
situations where wood cannot be easily dried.
Prevention
Chemical wood preservatives are an effective means of preventing wood
decay. Pressure treatment with preservatives such as creosote, zinc chloride,
pentachlorophenol, and/or copper naphthenate has been used extensively. The pest
management professional needs to be aware of the high toxicity of these chemicals.
Pentachlorophenol, for example, is no longer readily available to the consumer in
either the ready-to-use (5 percent penta) or the concentrated (40 percent penta)
formulation because of its high toxicity and status as a carcinogen. Pest
management professionals should be careful when handling pretreated wood. Wear
rubber gloves and long-sleeved clothing and wash thoroughly after handling.
Never dispose of preservative-treated wood by domestic incineration or use as a
fuel in fireplaces or wood-burning stoves. Treated wood, end pieces, wood scraps,
and sawdust should be disposed of at a sanitary landfill. Small quantities may be
disposed of with household trash.
ϯϱ
Control
Less toxic, more environmentally friendly fungicides than the pressure-
treated wood preservatives are commercially available. These fungicides are often
borate-based. To control fungi on existing wood structures, the wood should be
kept clean with periodic high-pressure washings and a fungicide application to kill
remaining fungal spores to prevent reinfestations. It is most important to point out
that the application of fungicides or insecticides to fungus-infested wood or soil
will not stop the wood decay. Only by eliminating the moisture source can wood
decay be completely controlled. Therefore, the application of chemicals by pest
management professionals is of minor importance in fungus control work.
Before the application of toxic chemicals for wood-destroying fungus
control (as is true for any aspect of pest control), all physical, sanitary, and other
means of control must be implemented. Not only will the control be more effective
in the end, but fewer chemicals or none at all, will be placed into the environment
where humans and animals may come into contact with them. Removal of all
sources of excessive moisture and replacement of obviously fungus-infested wood
with sound timber are the keys to fungus control in structures.
Borates as fungicides
A number of boron-containing products are available and referred to
JHQHULFDOO\ DV ³ERUDWHV´ 7KH ERUDWH NQRZQ DV GLVRGLXP RFWDERUDWH WHWUDK\GUDWH
(DOT) is actually a combination of several borates. Borates are well suited to
fungus control because they are low hazard, easy to apply, long lasting, and quite
effective against both fungi and wood-destroying insects. Part of their success as a
wood treatment can be attributed to their high solubility in water. They are easy to
mix in a water carrier and are carried along by water diffusing through the wood.
ϯϲ
They are available in a variety of formulations that allow spraying, brush-on,
gel, and foam applications. There is also a formulation available consisting of solid
rods that are inserted into holes drilled into the wood. These are designed for use in
wood with high moisture content that cannot be easily dried.
Biocontrol of Wood Decay by Trichoderma spp.
The microorganisms employed in biological control of fungi causing
diseases of plants and wood rots are termed as antagonists and an antagonist is a
microorganism that adversely affects another i.e. the target fungi causing rots and
diseases growing in association with it (Baker and Cook, 1974). Fungi have got
maximum attention as antagonists probably because of the fact that they are easy in
handling and in identification compared to other microbes. It has been suggested
that fungi serve as the most important antagonists of which the tendency of
Trichoderma spp. and others to produce broad spectrum antibiotics is well known
(Mukherjee
et al. 1992).
Degradation of ground contact wood by wood decay microorganisms is a
major problem for wood using industries. Wooden products have traditionally been
protected against soft rot and the basidiomycetes through the use of chemical
preservatives (Anon, 1994). Wood in ground contact is susceptible to a wide range
of wood decaying microorganisms. As a result, timber intended for use in ground
contact situation is generally treated using toxic chemicals such as copper chrome
arsenic, which protect the wood against the effects of biodegradation. However,
due to increasing awareness of the environmental impact of wood preservatives,
and the introduction of more straight legislation over operations at treatment sites
and the disposal of preservative treated wood, there has, over the last 25 years,
ϯϳ
been an upsurge of research into the potential of biological control as an alternative
technology. During this time, a number of authors (Cook and Baker 1983; Nelson
et al. 1995; Bruce 1998) have reported on the use of biological control agents in
agriculture, forestry and forest products.
More recently there has also been a very significant increase in the amount
of research into biological control of wood decay fungi as an additional strategy to
the use of chemical preservatives for wood protection (Freitag et al. 1991; Bruce
1992). This has mainly been due to the need for the wood preservation industry to
develop more environmentally safe and acceptable technologies for wood
protection at a time of heightened public concern on environmental issues (Philip
et al. 1995).
The possibility of employing the antagonistic effects of some fungi against
pathogenic fungi was first recognized more than 60 years ago (Weindling, 1934).
Successful application of biocontrol has since been reported in agriculture
(Campbell, 1989), horticulture (Papavizas, 1985) and in forestry (Risbeth 1975;
Mercer and Kirk 1984).
Biocontrol in agriculture is usually designed to protect a crop against a
narrow range of pathogens, possibly a single species, for a limited period of time,
often one growing season; conversely, wood products more commonly need to be
protected from a wide range of damaging microorganisms for the entire projected
service life of the product. While this may be a relatively short period of some
applications, e.g. paper pulp chip piles, in other instances the service life of the
wooden product may be many years. Despite these obvious differences in
requirements Trichoderma spp. have regularly been considered as potential
biocontrol agents for use in both agricultural and wood preservation application.
The choice of a biological control agent is very much limited by the
requirement for ecological compatibility between the control agent and its target.
ϯϴ
Trichoderma isolates are among the most widely researched biological control
agents for the production of agricultural crops from a variety of plant diseases
(Papavizas, 1985).
Trichoderma is currently the most extensively researched biocontrol fungus
in the field of forest products protection and has been shown on a number of
occasions to provide effect against certain wood decay fungi through the
production of various chemicals (Highley and Richard 1988; Bruce et al. 1984,
1996). Tucker et al. (1997) have shown that certain isolates of Trichoderma can
protect wood against basidiomycete decay fungi.
Trichoderma spp. has been a popular choice because they are well known to
antagonize other fungi by a variety of active and passive mechanism. Included in
the latter FDWHJRU\ZRXOGEHWKHRUJDQLVP¶VDELOLW\WR dominate substrates through
its fast growth rate, prolific spore production, metabolic versatility and tolerance of
environmental stresses particularly chemicals. Trichoderma are fast growing
primary colonizers of wood capable of utilizing the sugar present and thereby
inhibiting the growth of decay fungi (Hulme and Shields 1972).
Trichoderma spp. has also been reported to produce soluble antifungal
metabolites (Dennis and Webster 1971; Taylor 1976; Horvath et al. 1995), volatile
organic compounds (Bruce et al. 1984, 1996; Wheatley et al, 1997), Chitinase and
laminarinase (Bruce et al. 1995) and siderophores (Srinivasan 1993).
Mechanisms of Control
Mechanisms of control which have been attributed to Trichoderma spp. can
be categorized into the following types ± competition for nutrients (Hulme and
Shields, 1970), production of soluble metabolites (Dennis and Webster 1971,
Taylor 1976), production of inhibitory volatiles (Bruce et al. 1984),
ϯϵ
mycoparasitism involving the production of lytic enzymes (Elad et al. 1982; Chet,
1990; Ozbay and Newmann, 2004).
Trichoderma spp. has been reported (Anke et al. 1991, Dutta et al. 2006) to
produce siderophores (iron chelating compounds) and this may contribute to the
biological control of wood decay fungi. Competition for iron via siderophore
production has long been recognized as an important antagonistic trait of many
biological control agents of plant pathogens (Neilands 1984; Leong 1986; Bossier
1988, Rane et al. 2005, Machuca et al; 2007).
The research has shown that Trichoderma isolates are well able to control
decay by a variety of basidiomycete in soil block and agar test systems and has
highlighted the various control mechanisms, which the organisms may employ.
Mycoparasitism is a behavioural process involving a number of sequential
stages including target location, lysis and nutrient acquisition. Production of the
lytic enzymes and the factors, which influence the stages are, therefore, only one
aspect, which will determine the potential of any likely Trichoderma isolate for the
biological control of decay fungi (Bruce et al.1995). Mycoparasitism of plant
pathogenic fungi by Trichoderma isolates has been well researched (Harman et al.
1981; Chet et al.1981; Chet and Elad 1982; Chakraborty et al. 2004) and is widely
considered to be a major contributing factor to the biocontrol of Trichoderma spp.
of a range of commercially important plant disease.
Mycoparasitism may be a significant mode of antagonism of Trichoderma
isolates against wood decay fungi has been reported (Murmanis et al. 1988;
Srinivasan 1993; Bruce et al. 1995; Kundu and Chatterjee, 2003). Little work
however, has been reported on the importance of mycoparasitism in the biological
control of wood decay fungi by Trichoderma isolates. Murmanis et al. (1988)
regularly observed directed growth and hyphal interference by Trichoderma spp.
towards basidiomycete fungi when the two organisms were allowed to interact in
ϰϬ
wooden blocks. After a period of time, the Trichoderma isolates had totally
consumed the KRVWV¶cytoplasmic contents, indicating active mycoparasitism by the
control agents.
Lytic enzymes including chitinase and laminarinase have long been
recognized as being important in mycoparasitism of plant pathogen i.e., fungi by
Trichoderma spp. (Elad et al. 1982, Karasuda et al. 2003). While some
researchers, including Herman and Hayes (1993) have attempted to use protoplast
fusion to develop effective biocontrol strains, other researchers have concentrated
on improving single antagonistic trait during strain development. Haran et al.
(1993) considered that constitutive elevation of extracellular lytic activity could
improve the natural capability of T. harzianum to attack pathogens and its
consequent use as a biocontrol agent. One of the essential characters of fungal
biological control agent to act as mycoparasites of fungal plant pathogen is their
ability to excrete hydrolytic enzymes. Fluorescent indicators and enzyme studies
provided evidences for such enzyme activity leading to penetration of hypha by
mycoparasites (Baker and Dickman 1993). Hydrolytic enzymes such as glucanase,
chitinase, cellulase, xylanase, acid and alkaline phosphatase, esterase, lipase,
leucinearylaminidase, á- and â- glucosidase, N-acetylglucoaminidase and protease
are known to produce by Trichoderma upon induction (Elad et al., 1982, Aziz et
al.1993).
Inadequate understanding of microbial ecology, factors leading to sustained
performance of bio-control agent in natural environment and lastly the expectation
that bio-control agent will substitute for chemical in terms of instant results were
the main causes by which bio-control of wood decay has not been fulfilled its
promise. But to develop sustainable systems of wood decay protection, the role of
biological control method is unquestionably pivotal. To avoid chemical hazards
that depletes and degrades the resources of environment, wood rot management
ϰϭ
approach through bio-control agents has gained more attention recently.
Emergence of biotechnology, genetic engineering and plant immunization
technology will provide better solutions to control wood deterioration problems
and to develop broad-spectrum durable resistance of wood against decay fungi. It
is now well accepted that bio-control of wood rot fungi is an eco-friendly means
which has got distinct possibilities of successful exploitation in wood and timber
industry (Kundu, et al., 2002).
Bacteria as Bio-control Agents
Bacteria, though major contributors to the decay of waterlogged wood, are
much less important than fungi as agents of wood degradation (Eaton and Hale,
1993) and as such do not represent a significant target for biological control
systems. Over the past fifteen years, however, promising results have emerged by
using bacteria to control sapwood-inhabiting blue-stain fungi (Morrell and Sexton,
1993; Benko, 1989; Benko, 1998 and Bernier et al. 1986). Benko and Highley,
1990 evaluated the effectiveness of the bacterial cultures against blue stain and
mold fungi as well as BRF and WRF. They used a mixed bacterial solution
consisting of six bacteria from the genera Pseudomonas (P. cepacia), Streptomyces
(S. chrestomyceticus, S. rimosus and S. rimosus forma paromomycinus),
Streptoverticillium (S. cinnamoneum forma azacoluta), and Xenorhabdus (X.
luminescens). The mixed bacterial culture was found strongly antagonistic against
the wood-attacking fungi. Southern yellow pine (Pinus spp.) blocks treated with
the solution of mixed bacterial culture suffered less than 1% weight loss after two
PRQWKV¶H[SRVXUHWRWKH%5)Postia placenta) or WRF (T. versicolor). Laboratory
tests also indicated complete inhibition of blue-stain fungus, Ceratocystis
coerulescens or mold, Trichoderma harzianum over the same period of time.
ϰϮ
Actinomycetes as Biocontrol Agents
Over the past 55 years, actinomycetes have been the most widely exploited
group of microorganisms in the production of secondary metabolites of
commercial importance in medical and agricultural applications. Actinomycetes
and particularly Streptomyces spp. are good sources of novel antibiotics, enzymes,
enzymeinhibitors, immunomodifiers and vitamins. Their ubiquitous nature and
prolific metabolic activity has led to 4,607 patents for actinomycetes-related
products, including 3,477 antibiotics produced from Streptomyces alone (Williams
and Vickers, 1988; Demain, 1985). Actinomycetes are Gram-positive, filamentous
bacteria that are among the most abundant soil and rhizosphere microorganisms.
Like filamentous fungi they grow with branching hyphae and can penetrate
insoluble substrates, such as lignocellulose. Some of the examples of common
genera of lignocellulose-degrading Actinomycetes are Streptomyces,
Micromonospora, Microbispora, Thormomonospora, Norcardia and Arthrobacter
spp. (Finolow and Locwood, 1985; Crawford et al. 1993). Lignin degradation is a
primary metabolic activity in the case of Streptomyces in contrast to
Phanerochaete chrysosporium, where it is a secondary metabolic activity (Wang et
al. 1991).
Streptomyces are important saprophytic soil microorganisms and well-
known producers of antibiotics and extracellular enzymes (Rothrock and Gottlieb,
1984). They are primarily degraders of grass-type lignocelluloses. Streptomyces
spp. solubilizes lignin but their mineralization of lignin to CO
2
is much less than
that of other WRF (Pasti et al. 1990; Wang et al. 1991; Ruttimann et al. 1991).
This low wood lignin mineralization ability of Streptomyces spp. means that
Streptomyces and other actinomycetes may be useful as bio-control agents without
much concern over their wood-decaying ability. Their bio-control abilities clearly
correlate with the production of antibiotics (Hwang et al. 1994). Streptomyces
ϰϯ
violaceusniger YCED9, for example, is a soil isolate which exhibits bio-control
activity against a variety of plant pathogenic fungi. The strain produces at least
three antifungal antibiotics, including Nigericin, Geldanamycin and a complex of
polyenes that includes Guanidylfungin A15. Streptomyces spp. are also known for
their ability to cause lysis of fungal hyphae by producing chitinases and glucanases
as already mentioned. The antifungal bio-control agent, S. lydicus WYEC108 was
capable of not only destroying germinating oospores of Pythium ultimum but also
damaging the cell walls of the fungal hyphae (Yuan and Crawford, 1995).
WYEC108 also produced high levels of chitinases, induced to high levels as fungal
cell walls are used as a carbon source in growth media. However, negligible levels
of enzymes were detected when S. lydicus WYEC108 was grown in the absence of
chitin. Chitinase production by S. lydicus WYEC108 was also induced by colloidal
chitin, N-acetylglucosamine and chito-oligosaccharides. However, the synthesis
was repressed by high (but not low) levels of glucose and carboxy methyl cellulose
(CMC) (Mahadevan and Crawford, 1997).
Actinomycetes Fb352 was reported to possess antagonistic activity against
fungi, Aureobasidium pullulans and Hormonea dematodes (Bezert et al. 1996;
Roussel et al. 2000). Many such reports are available in the literature that is related
to the production of antibiotics antagonistic to several other fungi. These antibiotic
substances induce malformations in fungi, such as stunting, distortion, swelling,
hyphal protuberances or the highly branched appearance of fungal germ tubes, an
indirect evidence to show antibiosis as a mechanism of antagonism. Using such
criteria, it was detected that antibiotics of some soil actinomycetes caused similar
effects on hyphae of Helminthosporium sativum, in culture and in soil. Several
species from Streptomyces violaceusniger clade produced antifungal antibiotics,
such as Niphithricin, Spirofungin, Azalomycin F complex, Guanidylfungins and
Malonylniphimycin (Getha and Vikineswary, 2002).
ϰϰ
Soil and aquatic actinomycetes show considerable ability to survive
starvation. Antibiotics and protein inhibitors are formed during the late growth
cycle, when familiar regulatory processes, like transcriptional control, are
ineffective. These secondary metabolites can prevent degradation of enzymes and
structural proteins essential for survival as well as biosynthesis, which might form
aberrant products during nutrient limitation. Interestingly, secondary metabolite
production in Streptomyces spp. is subject to catabolic repression in the presence
of high levels of carbon and nitrogen sources. Repression of secondary metabolite
biosynthesis by ammonia or certain amino acids is common in actinomycetes.
Nitrogen limiting conditions lead to the secretion of ligninases responsible for
wood degradation by WRF, like P. chrysosporium. Low nitrogen conditions would
also be conducive to the secretion of antifungal and antibacterial secondary
metabolites by actinomycetes used as bio-control agents (Demain, 1985).
Of all the potential bio-control agents for use in controlling fungal wood
decay, actinomycetes and particularly Streptomyces spp. are among the best
sources of novel antifungal antibiotics, enzymes and enzyme inhibitors. Thus, they
have great potential to be exploited as broad-spectrum bio-control agent against
wood bio-deterioration caused by fungi. However, the future development of
biological control systems for wood protection or treatment will ultimately depend
on how they measure up against traditional chemical preservatives. New biological
systems must perform well under field conditions; be competitive in terms of
stability and product cost; be easy to apply, store and handle; and satisfy the same
level of stringent testing and regulatory control which is required during the
development of any new chemical wood preservative. Only when a bio-control
agent has fulfill all the above, the wood preservative industries can happily
embrace the technology.
ϰϱ
Tree-derived Phenolic Compounds as Control Agents for Wood-
decaying Basidiomycetes
Naturally occurring phenolic compounds were used as possible regulators of
fungal growth. Taylor et al. (1987) reported that the growth of Trametes versicolor
on wood was affected in a bimodal fashion via time-dependent application of
catechol. Data from other studies also indicated that phenolic compounds
(quinones) might regulate hyphal growth in a bimodal fashion through the products
of extracellular polyphenol oxidase (Taylor et al. 1989).
The effect of 12 monomeric aromatic compounds on the production of six
carbohydrate-degrading enzymes from two BRF, Postia (Oligoporous) placenta
and Gloeophyllum trabeum, and one WRF, Trametes versicolor was reported by
Highley and Micales, 1990. Most compounds at a concentration of 0.05% (w/v)
were inhibitory to the growth of the decay fungi. When incorporated into the liquid
growth medium of the fungi, some of these compounds inhibited the production of
enzymes. Catechol and vanillin (50 ppm) caused complete inhibition of xylanase
DQG ȕ-1, 4-endoglucanase production by P. placenta. No aromatic monomer,
however, strongly inhibited all enzyme activities of all of the fungi. Interestingly,
the efficacy of phenolic fraction of the Hopea parviflora heartwood and Cashew
nut shell liquid was investigated against termites and fungi (Ramadevi et al. 2002;
Krishnan et al. 1993). They found the results encouraging; however, further
examination for the efficacy of phenolic compounds as fungal growth control
agents is required.
ϰϲ
Chapter: 5
WOOD-STAINING FUNGI
Wood staining fungi can cause bluish, brownish or other shades of
discolouration, often limited to sapwood. As a rule, the fungi settle first in the rays.
7KLVLVEHFDXVHWKH\FDQ¶WDFWXDOO\GHJrade the substance of the wood and live on
FDUERK\GUDWHVDQGIDWVZKLFKDUHVWRUHGLQWKHVDSZRRGUD\V$OWKRXJKWKH\GRQ¶W
destroy the wood, permanent staining can greatly reduce its value.
What kind of staining occurs frequently?
Stains caused by sapstain fungi and mould are particularly common in
coniferous timbers. The sapstain fungi can also grow into the wood so that the stain
penetrates deeply. This makes it impossible to plane the stain away mechanically.
Mould only discolours wood on the surface through its spores, but often leaves
mould stains after their removal. Special anti-sapstain preservatives, that should be
applied directly after the timber is cut, provide protection against wood-staining.
Is staining always caused by fungi?
Not all stains are caused by microorganisms. Dirt and dust particles on the
ZRRG¶VVXUIDFHFDQEHPLVWDNHQIRU PRXOG&XWZRRG FDQUHDFWWRLURQSDUWLFOHV
also resulting in stains. Such stains occur in wood types that contain tanning
agents, like oak and sweet chestnut, but also Douglas fir, when they come into
contact with iron or water with high iron content during storage or processing. The
phenolic content in the wood reacts with the iron ions and forms dark
colourings. Besides, wood can also suffer discolouration in the living tree, as is the
case with red heartwood formation in beech trees.
Sapstain / Blue stain fungi
ϰϳ
Blueing, blue stain or sapstain are terms used to describe wood that shows
blue to greyish-black stains on its surface, caused by wood-staining fungi. Sapstain
is considered a fault in timber and will be taken into account when sorting. The
fault is that the discolouration of the wood makes it unsuitable for some
applications. Sapstain fungi live on the content of wood cells. The wood itself is
not destroyed (no rot formation).
Which fungi cause sapstain?
The discolouration is caused by fungi of the Acomycetes or the Fungi
imperfecti (Deuteromycetes) groups. Today, there are between 100 and 250
different known species of blue-stain or sapstain fungi. Among the most significant
species of sapstain fungi are Ceratocystis (from the Acomycetes) as well as
Aureobasidium, Alternaria und Cladosporium (from the Deuteromycetes group).
The blue staining is often the result of a mixed infestation. To determine the
individual species, subcultures of the fungi and microscopic examination are
required.
How is the wood attacked?
Sapstain damage occurs mainly in coniferous wood. Pine timbers are
particularly susceptible, but also spruce, fir, or larch timbers, as well as certain
deciduous wood types like beech or imported timbers, such as Limba, Ramin or
Brazil pine can be attacked by sapstain fungi. Infection of the wood can happen in
different ways. Spores can spread through the air, or be carried by insects or
rainwater. Infection can be different depending on the fungus species. Some fungi
depend on insects, others depend exclusively on air. Sapstain fungi also have
different requirements regarding habitat, for which important determining factors
are temperature and wood moisture.
ϰϴ
What different kind of sapstain fungi are there?
There are three main kinds: trunk wood sapstain, sawn timber sapstain and
sapstain occurring in timber coatings.
The fungi causing trunk wood sapstain attach very damp wood and can
infest logs lying in forests. Though freshly cut wood is not usually attacked, the
slightest reduction in moisture can result in sapstain fungi spreading into the
sapwood. Sapstain in trunk wood is mainly caused by the Ceratocystis and
Ophiostoma species. (Photo: protected wood - unprotected wood with sapstain)
Fungi that cause sapstain in sawn timbers tend to attack slightly drier wood,
like freshly cut planks and boards. They mainly occur in storage places after the
trunks have been cut, in planks and boards that are badly stacked and not
sufficiently dried.
The final strain occurs in wood that has already been processed and used in
some application, either coated or not. Moisture and fungal spores can penetrate
the wood through cracks in the coating. The fungi grow underneath the coating and
form fruiting bodies that can raise this coating layer and cause damage after the
wood has been put to its final use.
Why does the wood turn blue?
ϰϵ
The spores germinate and develop into hyphae. After dividing numerous
times, the sapstain mycelia are formed. This is hyaline (glassy or transparent) to
begin with and spreads through the wood interior, mainly in the rays. In the course
of its development, dark brown pigments (melanins) are formed in the hypha. The
blue colouring comes from the hyphae of sapstain fungi - which have been
darkened by the melanins inside them - shimmering through to the wood surface.
The blue appearance is therefore no more than an optical illusion, similar to that
which occurs with cigarette smoke which also appears to be blue, though the ash
particles are actually black. The colour of blue-stained wood depends on the
concentration of the pigments and consequently from the number of hyphae in the
wood. The more hyphae, the darker the colour.
How can sapstain be prevented?
The risk of infestation from trunk wood sapstain can be significantly reduced
by the correct choice of felling time, optimization of log storage and, above all, by
processing the timber quickly.
During the drying phase of freshly felled logs in the saw mill, the risk of
sawn timber sapstain is especially high. Temporarily effective, environmentally
compatible anti-sapstain products protect the wood during the drying phase and
prevent massive losses in its value. Correct priming impregnation treatment, using
the double vacuum process, for instance, will reliably prevent the occurrence of
sapstain and consequently eliminate costly and time-consuming renovation of
painted and coated timbers.
ϱϬ
SAP-STAIN FUNGI
Some Ascomycetous fungi colonize the soft (parenchymatous) tissues of
freshly felled wood. These sap-stain fungi can be economically damaging because
they discolour the wood and lower its value.
The most conspicuous of these fungi is Chlorociboria aeruginascens (Fig.
1), also known as "Green wood-cup". It is a member of the Ascomycota, quite
often seen on fallen branches of oak or alder (Alnus glutinosa). The hyphae grow
through the wood and stain it a blue-green colour. Small blue-green apothecia are
sometimes seen on the surface of colonized wood, but are not common.
Fig 10. Blue-stained wood of alder (Alnus glutinosa) naturally colonised by the
blue-pigmented hyphae of Chlorosplenium aeruginascens. This type of coloration
is quite common in fallen branches of alder and oak.
At one time, a local industry was built up in Kent (Southern England) to
produce high-quality veneers for cabinet-making or for small ornaments. Naturally
ϱϭ
stained woods of different colors were compressed into blocks of different
patterns. The resulting products were termed "Tunbridge ware" because the
industry was based around the town of Tunbridge Wells.
Other sap-stain fungi can cause problems in commercial forestry because
they rapidly colonize the soft, parenchymatous tissues of felled timber, causing the
wood to be discolored and reducing its value. Trichoderma spp are among the most
important in this respect - especially in softwoods such as pine (Figs 2 and 3,
below).
Fig. 11. Sporulation of Trichoderma spp. on the exposed ends of two split pine
logs, about 3 months after the logs were felled. The fungus is seen as radiating
ϱϮ
zones of white and grey-green sporing structures. The hyphae rapidly colonize the
wood longitudinally, causing internal discoloration.
Fig. 12. Close-up view of part of Fig. 11.
BIOLOGICAL CONTROL OF SAPWOOD STAINING FUNGI
When trees are cut fungi can
rapidly colonize the sapwood and cause a
dark stain. This stain often appears blue
or black and reduces the quality of the
wood. Blue stain in pine and other
coniferous woods is very common but
dark stains also form in hardwoods like
maple, birch and beech. The aggressive
sap-staining fungi that cause the stain are
very difficult to control and in the past
Blue stain in pine
ϱϯ
chemicals such as pentachlorophenol
have been used to protect cut wood
surfaces from stain. Our research has
focused on a new approach to controlling
sapstain using biological control.
Naturally occurring albino strains of
Ophiostoma are being tested to control
dark staining fungi. The biocontrol agent
is applied immediately after cutting and
as it grows in the wood it captures
nutrient resources that stain fungi
normally use. Since the fungus is
colorless, there is no stain caused by the
biocontrol agent. Once established, the
albino strain effectively prevents
subsequent colonization by fungi that
cause dark stains in wood. Field testing is
underway in New Zealand (in
cooperation with Professor Roberta
Farrell, University of Waikato, Hamilton,
New Zealand) and in Chile (in
cooperation with Professor Jose
Navarrete, University of Bio-Bio,
Conception, Chile) using Pinus
radiata. This tree grows very fast in these
countries and consists mostly of sapwood
Blue stain occurs during transport and
storage of cut wood and is often
associated with bark beetles
Biocontrol field trial in New Zealand
ϱϰ
which is severely affected by blue stain
fungi.
Pioneer colonizing white rot
fungi are also being used as biological
control agents to prevent stain in wood
used for pulp and paper production.
Fungi such as Phlebiopsis gigantean
(previously called Peniophora
gigantea) have been used to treat
pulpwood during shipping and storage.
The treatment prevents stain fungi and
causes beneficial changes in the wood
that helps to facilitate the pulping
process (such as reduced energy use
during mechanical pulp production and
improved paper qualities).
Wood chips treated with biocontrol
fungus before pulping
ϱϱ
REFERENCES:
Anke, H., Kinn, J., Bergquist, K. E. and Sterner, O. 1991. Production of
siderophores by strains of the genus Trichoderma. Isolation and
characterisation of the new lipophilic coprogen derivative palmitoyl
coprogen. Biometals, 4(3): 157-165.
Aziz, A. Y., Fosterm H. A. and Fairhurst, C. P. 1993. Extracellular enzymes
of Trichoderma harzianum, T. polysporum and Scytalidium lignicola
in relation to biological control of Dutch elm disease. Arboric. J., 17:
159-170.
Backer, R. and Dickman, M. B. 1993. Biocontrol with fungi. In: Soil
Microbial Ecology ± Application in Agricultural and Environmental
Managerment (Ed. F. Blaine Meeting Jr. ) Marcel Dekker. Inc. New
York. pp. 275-306.
Benko, R. and Highley, T. L. 1990. Evaluation of bacteria for biological
control of wood decay (Int Res Group on Wood Preserv, Sweden),
Document No.IRG/WP/1426.
Benko, R. 1998. Bacteria as possible organisms for biological control of
blue stain, International Research Group on Wood Preservation,
Document No.IRG/WP/1339.
Benko, R. 1989. Biological control of blue stain on wood with Pseudomonas
cepacia 6253: laboratory and field test (Int Res Group on Wood
ϱϲ
Preserv, Sweden), Document No. IRG/WP/1380.
Bernier, R. Jr., Desrochers, M. and Jurasek, L. 1986. Antagonistic effects of
Bacillus subtilis and wood staining fungi. J Inst Wood Sci, 10: 214-
216.
Bezert, G., Chappe, P., Mourey, A. and Loubinoux, B. 1996. Action de
%DFLOOXVHW Actinomycetes sur les champignons de bleuissement du
bois. Comptes Rendus Acad Soc Lorraines Sci, 35/3: 177-190.
Bossier, P., Hofte, M. and Verstracte, W. 1988. Ecological significance of
siderophores in soil. Advances in Microbial Ecology, 10: 385-414.
Bruce A. (1992): Biological control of wood decay. International Research
Group on wood preservation. Document No. IRG/WP/ 1531-92.
Bruce, A. 1998. Biological control of wood decay In: Forest Products
Biotechnology. Eds. Bruce, A. and Palfreyman, J. H. Taylor and
Francis. London. pp. 251-267.
Bruce, A., Austin, W. J. and King, B. 1984. Control of growth of Lentinus
lepideus by volatiles from Trichoderma. Trans. Brit-Mycol. Soc., 82:
423-428.
Bruce, A., Kundzewicz, A. and Wheatley, R. E. 1996. Influence of culture
age on the volatile organic compounds produced by Trichoderma
ϱϳ
aureoviride and associated inhibitory effects of wood decay fungi.
Mat. und. Org. 30(2): 79-94.
Bruce, A., Srinivasan, U., Staines, H. J., and Highley, T. L. 1995. Chitinase
and laminarinase production in liquid culture by Trichoderma spp.
and their role in biocontrol of wood decay fingi. Int. Biodet and
Biodeg., 35(4): 337-353.
Chakraborty, M. R., Dutta, S., Ojha, S. and Chatterjee, N. C. 2004.
Antagonistic potential of biocontrol agents against Botryodiplodia
theobrome causing die-back of Bottle brush (Callistemone citrinus).
Acta Botanica Hungarica, 46(3-4): 279-286.
Chet, I. 1990. Biological control of soil-borne plant pathogens. (Hornby
C.A.B., ed.) pp. 15-26.
Chet, I. and Elad, Y. 1982. Prevention of plant infection by biological
means. In La Selection des Plantes, Bordeoux (France). Colloq II
NRA Vol. II pp. 192-204.
Chet, I., Harman, G. I. and Baker, R. 1981. Trichoderma hamatum its hyphal
interactions with Rhizoctonia solani and Pythilum spp. Microb. Ecol.,
7: 19-38.
Cook, R. J. and Baker, K. F. 1983. The nature and practice of biological
control of plant pathogens. American Phytological Society, St. Paul,
M.N.
ϱϴ
Crawford, D. L., Lynch, J. M., Whipps, J. M. and Ousley, M. A. 1993.
Isolation and characterization of actinomycetes antagonist of a fungal
root pathogen. Appl Environ Microbiol, 59: 3889-3905.
Demain, A. L. 2000. Control of secondary metabolism in actinomycetes, in
Proc Sixth Int Symp on Actinomycetes Biology, edited by G Szabo, S
Biro & M Goodfellow (Akademiae Kiado Press, Budapest) 1985,
215-225 [Demain, A L, Biotechnol Adv, 8 (1990) 291-301 & Microb
Biotechnol, TIBTECH, 18: 26-31].
Dennis, C. and Webster, J. 1971. Antagonism properties of species groups of
Trichoderma. I. Production of non-volatile antibiotics. Trans. Brit.
Mycol. Soc., 57 (I):47-48.
Dennis, C. and Webster, J. 1971. Antagonism properties of species groups of
Trichoderma. I. Production of non-volatile antibiotics. Trans. Brit.
Mycol. Soc., 57 (I):47-48.
Dutta, S., Kundu, A., Chakraborty, M. R., Ojha, S., Chakraborty, J. and
Chatterjee, N. C. 2006. Production and Optimization of Fe (III)
specific ligand, the siderophore of soil inhabiting and wood rotting
fungi as deterrent to plant pathogens. Acta Phytopathol. Entomo.
Hung., 41(3-4): 237-248.
Eaton, R. A. and Hale, M. D. C. 1993. Wood decay, pests and protection
(Chapman & Hall, London).
ϱϵ
Elad, Y., Chet. F. and Henis, Y. 1982. Degradation of plant pathogenic fungi
by Trichoderma harzianum. Can. J. Microbiol., 28: 719-725.
Elad, Y., Chet, F. and Henis, Y. 1982. Degradation of plant pathogenic fungi
by Trichoderma harzianum. Can. J. Microbiol., 28: 719-725.
Finolow, A. B. and Lockwood, J. L. 1985. Evaluation of several
Actinomycetes and the fungus Hypochytrium catenoides as biocontrol
agent for Phytophthora root rot of soyabean. Plant Dis, 69: 1033-
1036.
Freitag, M., Morrell, J. J. and Bruce, A. 1991. Biological protection of
wood: status and prospects. Biodeterioration Abstracts, 5: 1-12.
Getha, K. and Vikineswary, S. 2002. Antagonistic effects of Streptomyces
violaceusniger strain G10 on Fusarium oxysporum sp. cubense race 4:
Indirect evidence for role of antibiosis in the antagonistic process. J
Ind Microbiol Biotechnol, 28: 303-310.
Haran, S., Schiekler, H., Peer, S., Longemann, Oppenheim, A. and Chet, I.
1993. Increase constitutive chitinase activity in transformed
Trichoderma harzianum. Biol. Control, 3: 101-108.
Harman, G. E., Chet, I. and Baker, R. 1981. Factors affecting T. hamatum
applied to seeds as a biocontrol agent. Phytopathology, 71: 569-572.
ϲϬ
Harman. G. E. and Hayes, C. 1993. The genetic nature and biocontrol ability
of progeny from protoplast fusion in Trichoderma. In Biotechnology
in Plant Disease Control, ed. I. Chet. Chap. 12, pp. 237-236. Wiley-
Liss, New York.
Highley, T. L. and Micales, J. A. 1990. Effect of aromatic monomers on
production of carbohydrate-degrading enzymes by white-rot and
brown-rot fungi. FEMS Microbiol Lett, 66: 15-21.
Highley, T. L. and Ricard, J. 1988. Antagonism of Trichorderma spp. and
Glioccladium virens against wood fungi. Mat. and Org., 23: 157-169.
Horvath, E. M., Burgel, J. L. and Messner, K. 1995. The production of
soluble antifungal metabolites by the biocontrol fungus Trichoderma
harzianum in connection with the formation of conidiospores. Mat.
und. Org., 29(1):1-14.
Hulme, M. A. and Shields, J. K. 1972. Effect of primary fungal infection
upon secondary colonisation of birch bolts. Mat. und. Org., 7: 177-
178.
Hwang, B. K., Ahn, S. J. and Moon, S. S. 1994. Production, purification and
antibiotic activity of the antibiotic nucleoside, tubericidin produced by
Streptomyces violaceusniger. Can J Bot, 72: 480-485.
ϲϭ
Karasuda, S., Tanaka, S., Yamamoto, Y. and Koga, D. 2003. Plant chitinase
as a possible biocontrol agent for use instead of chemical fungicides.
Bio Sci. Biotech. and Biochem., 67(1): 221-224.
.LUN7.DQG)DUUHOO5/(Q]\PDWLF³FRPEXVWLRQ´7KHPLFURELDl
degradation of lignin. Annu Rev Microbiol, 41: 465-505.
Krishnan, R. V., Theagrajan, K. S., Ananthapadmanabha, H. S., Sharma, M.
N. and Prabhu, V. V. 1993. Biocidal property of phenolic fraction of
ethanol extractives of Hopea parviflora heartwood (Int Res Group on
Wood Protection, Sweden), Document No. IRG/WP/93-3003.
Kundu, A. and Chatterjee, N. C. 2003. Antagonism of Trichoderma species
to Polyporus sanguineus-an incitant of bamboo decay. The Indian
Forester, 129(10): 1281-1288.
Kundu, A., Chakraborty, M. R., Dutta, S. and Chatterjee, N. C. 2002.
Inhibition potential of Trichoderma spp. against bumboo rot caused
by Irpex mollis. Tropical Mycology. Proc. Natn. Symp. On Trop.My.
of 21st century. pp. 207-211.
Leong, J. 1986. Siderphores. : Their biochemistry and possible role in the
biocontrol of plant pathogens. Ann. Rev. Phytopathol. 24: 184-209.
Machuca, A., Pereira, G., Aguilar, A. and Milagres, A. M. F. 2007. Metal-
chelating compounds by ecotomycorrhizal fungi collected from pine
plantation in southern chile. Lett. Appl. Microbiol., 44(1):7-12.
ϲϮ
Mahadevan, B. and Crawford, D. L. 1997. Properties of the chitinase of the
antifungal biocontrol agent Streptomyces lydicus WYEC108. Enzyme
Microb Technol, 20: 489-493.
Mercer, P. C. and Kirk, S. A. 1984. Biological treatments for the control of
decay in tree wounds ± II . Field tests. Ann. Appl. Biol., 104: 211 ±
219.
Morrell, J. J. and Sexton, C. M. 1993. Fungal staining of ponderosa pine
sapwood: effects of wood preconditioning and bioprotectants, Wood
Fiber Sci, 25: 322-325.
Mukherjee, K. G., Tewari, J. P., Arora, D. K. and Saxena, G. 1992. In:
Recent Development in Biocontrol of plant diseases. Aditya Book
Pvt. Ltd., New Delhi, pp. 1-195.
Murmanis, L., Highley, T. L. and Palmr, J. G. 1988. The action of isolated
brown rot cell free culture filtrate, H2O2-Fe3+ and the combination of
both on wood. Wood Sci. Technol., 22: 59-69.
Neilands, J. B. 1984. Siderophores from bacteria and fungi. Microbiological
Science, 1: 9-14.
Nelson, E. E., Pearce, M. H. and Malajezuk, N. 1995. Effect on
Trichoderma spp. and ammonium sulfamate on establishment of
ϲϯ
Armillaria luteobubalina on stumps of Eucalyptus diversicolor.
Mycological Research, 99:957-962.
Ozbay, N. and Newman, S. E. 2004. Biological control with Trichoderma
spp. with emphasis on Trichoderma harzianum. Pakistan Jr. of
Biological Sciences, 7(4): 478-484.
Papavizas, G. C. 1985. Trichoderma and Gliocladium. Biology, ecology and
potential for biocontrol. Ann. Rev. Phytopathol., 23:23-54.
Pasti, M. B., Pometo, III A. L., Nuti, N. P. and Crawford, D. L. 1990. Lignin
degrading ability of actinomycetes isolated from termite (Termitidae)
gut. Appl Environ Microbiol, 56: 2213-2218.
Philp, R. W., Bruce, A. and Munro, A. G. 1995. The effect of water soluble
scots pine (Pinus sylvestris L.) and Sitka spruce [ Picea sitchensis
(Bong.) carr.] heartwood and sapwood extracts on the growth of
selected Trichoderma species. International Biodeterioration and
Biodegradation. pp. 335-337.
Ramadevi, O. K., Nagaveni, H. C., Raja, M. and Sharma, M. N. 2002.
Evaluation of the efficacy of Cashew nut shell liquid based products
(CSNL) against termites and fungi. Timber Dev Assoc, 48(3-4): 15-
19.
Rane, M. R., Naphada, R. Z. and Chincholkar, S. B. 2005. Methods for
microbial iron chelator (siderophore) analysis in basic researches and
ϲϰ
applications of mycorrhizae. Edited by Gopi K Podila and Verma
A.I.K. Internatn. Pvt. Ltd. pp. 475-492.
Risbeth, J. 1975. Stump inoculation; a biological control of Formes annosus.
Biology and control of soil-borne plant pathogens (Bruchel,
G.W.,ed.). Amer. Phytopalthol. Soc., St. Paul. pp. 158 ± 172.
Rothrock, C. S. and Gottlieb, D. 1984. Role of antibiosis in antagonism of
Streptomyces hygroscopicus var. geldanus to Rhizoctonia solani in
soil. Can J Microbiol, 30: 1440-1447.
Roussel, C., Bezert, G., Bucur, V., Gerardin, P. and Loubinoux, B. 2000.
Evaluation of wood degradation during biological treatment with
actinomycetes. Holz als Roh-und Werkstoff, 58: 127-128.
Ruttimann, C., Vicuna, R., Mozuch, M. D. and Kirk, T. K. 1991. Limited
bacterial mineralization of fungal degradation intermediates from
synthetic lignin, Appl Environ Microbiol, 57: 3652-3655.
Srinivasan, U. 1993. A study of mechanisms of antagonism by the
biocontrol fungi Trichoderma against wood decay basidiomyctes Ph.
D. Thesis. Dundee Institute of Technology, pp. 285.
Taylor, A. 1976. Some aspects of the chemistry and biology of the genus
Hypocrea and its anamorphs., Trichoderma and Gliocladium. Proc. N.
C. Inst. Sci., 36: 27-58.
ϲϱ
Taylor, R., Lelwellyn, G. C., Mayfield, J. E., Shortle, W. C. and Dashek, W.
V. 1987. Time-dependent appearance of extracellular polyphenol
oxidase in relation to bimodal growth response of C. versicolor to
catechol, in Biodeterioration research I, edited by G C Lelwellyn & C
E O'Rear (Plenum Press, New York), pp. 63-74.
Taylor, R., Lelwellyn, G. C., O'Rear, C. E., Myfield, J. E. and Smith, K. T.
1989. In vitro growth of C. vesicolor, a wood-decay fungus, responds
differentially to catechol and tannic acid, in Biodeterioration research
II, edited by G C Lelwellyn & C E O'Rear (Plenum Press, New York),
pp. 451.
Tucker, E. J. B., Bruce, A. and Staines, H. J., 1997. Application of modified
international wood preservation chemical testing systems standards
for assessment of biocontrol treatments. International
Biodeterioration and Biodegradation, 39 (2-3): 189-197.
Wang, Z., Crawford, D. L., Magnuson, T. S., Bleakley, B. H. and Hertel, G.
1991. Effects of bacterial lignin peroxidase on organic carbon
mineralization in soil, using recombinant Streptomyces strains. Can J
Microbiol, 37: 287-294.
Weindling, R. 1934. Studies on lethal principles effective in the parasite
action of Trichoderma lignorum,onRhizoctonia Solani and other soil
fungi. Phytopathol., 24: 1153-1179.
ϲϲ
Wheatley, R. E., Hackett, C., Bruce, A. and Kundzewiez, A. 1997. Effects of
substrate composition on the production of volatile organic
compounds from Trichoderma spp. inhibitory to wood decay fungi.
Int. Biodet. and Biodeg., 39 (2-3): 199-205.
Williams, S. T. and Vickers, J. C. 1988. Detection of actinomycetes in the
natural environment²Problems and perspectives, in Biology of
Actinomycetes, edited by Y Okami, T Beppu & H Ogawara (Japan
Scientific Societies Press, Tokyo), pp. 265-270.
Yuan, W. M. and Crawford, D. L. 1995. Characterization of Streptomyces
lydicus WYEC108 as a potential biocontrol agent against fungal root
and seed rots. Appl Env Microbiol, 61: 3119-28.
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