WOOD DECAY

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WOOD DECAY

• Unique arrangement of fruiting bodies (aka
  sporophores, conks).
• Order Aphyllophorales (aka Polyporales) - bracket
  fungi.
• i. Hymenium lines small pores on underside of
  sporophore.
• ii. Important genera Polyporus, Fomes
• Order Agaricales - mushrooms.
• i. Hymenium lines gills (lamellae).
• ii. Important genera Armillaria, Agaricus

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Bracket Fungi

• Sporophores - bottom is covered with pores, each
  of which is lined with the hymenium, i.e., the
  spore-producing surface. On the hymenium are
  gazillions of basidia, each producing four
  basidiospores.

• Sporophores can be annual or perennial, depending
  on the pathogen, When perennial, they grow in
  size each year. They can be cut open to reveal
  'annual rings'.

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Mushrooms
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Characteristics of wood decay

• Defined as degradation of wood cell walls.
• b. Primarily caused by Basidiomycetes, although
  there are a few decays caused by Ascomycetes and
  Imperfect Fungi.
• c. Most decay fungi are secondary invaders. They
  do not (generally) colonize freshly wounded wood
  but generally require some degree of substrate
  modification before they can infect.
• d. Although some decays are sapwood decays, most
  occur in the heartwood, which is the central
  column of essentially dead wood in a tree. This
  wood must be exposed for decay fungi to be able
  to colonize and begin decay.

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Characteristics of wood decay

• e. Decay fungi undergo a process called
  autolysis. Mycelia generally are not found in
  wood in advanced stages of decay. Chitin in
  fungal cell walls contains much N and wood
  contains small amounts of N. This enables fungi
  to produce large fleshy or woody sporophores and
  billions of basidiospores, both of which contain
  much N.
• f. Decay occurs only under certain conditions
• i. Appropriate temperature (15 - 30 C). Some
  thermophilic fungi in chip piles can work at
  temperatures up to 45 C.
• ii. Appropriate moisture. Some moisture must
  be in the cell lumen for decay to occur. For most
  wood, the moisture content at which there is no
  moisture in the lumen is 20-25. This is termed
  the fiber saturation point. Wood will last
  indefinitely if moisture is kept below FSP.
• Moisture content (wet wt. - dry wt. / dry
  wt.) x 100
• Note If wood is saturated, decay will not occur
  even though moisture gt FSP. This is due to
  anaerobic conditions in wood.

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Characteristics of wood decay

• g. There are two basic types of wood decay. These
  differ based on ability to change the length of
  cellulose molecules.
• i. White rots - these fungi produce enzymes
  (exocellulases) that attack cellulose molecules
  from the ends. Although decayed, wood still
  retains some strength and usefulness, i.e., for
  pulpwood fiber, etc.
• ii. Brown rots - these fungi produce enzymes
  (endocellulases) that attack cellulose molecules
  in the middles. Decayed wood is crumbly, in
  cubes, and is totally useless. Even though it may
  weigh the same as the white-rotted wood, the
  brown-rotted wood is useless.

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Root Rot of Trees
Ex. of White Rot
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Rhizomorphs of Armillaria sp. adhering to roots
of apple
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• The phloem (inner bark) and cambium of this paper
  birch tree are being killed as a mycelial fan
  grows between the bark and wood. The black
  tissues immediately near the fan are dead.

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Humongous Fungus

• The underground fungus--estimated to be between
  2000 and 8500 years old.
• The clone of Armillaria ostoyae - the
  tree-killing fungus that causes Armillaria root
  disease--covers an area of 9.65 square
  kilometers, about the size of 6000 hockey rinks
  or 1600 football fields.
• "It's one organism that began as a microscopic
  spore and then grew vegetatively, like a plant,"

http//www.sciencedaily.com/releases/2003/03/03032
7074535.htm
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Modes of entrance for wood decay fungi

• a. Wounds
• Fire - a major infection court. Causes typical
  wound, called a 'cat face'.
• Logging wounds - severity depends on size and
  depth of wound. There is direct relationship
  between wound size and time required for healing.
  Anything gt 3" in any direction greatly increases
  time required for healing and, as such, increases
  likelihood for decay fungi to establish. Any
  wound that exposes heartwood is a decay risk.
• Blazing - with an axe. USE PAINT!!
• Storms - damage due to wind, ice, etc. Conifers
  more resistant than hardwoods, due to tree
  architecture.

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Modes of entrance for wood decay fungi

• Wounds
• Cankers - some diseases cause cankers on tree
  trunks and branches. If these expose heartwood,
  then decay organisms can become established.
• Seams - vertically oriented cracks that results
  from excessive heat, freezing, sun exposure.
• Frost cracks (i.e., 'Southwest disease') occur
  as a result of differential rates of wood
  expansion in direct sunlight in winter.
• Insects - bore holes in wood and expose
  heartwood..

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Modes of entrance for wood decay fungi

• b. Branch stubs - many folks do not know how to
  prune.
• Prune only branches lt 3" in diameter. This
  prevents heartwood from being exposed
• Prune such that natural healing is promoted.
• DO NOT use wound dressings. They serve only to
  trap moisture and make heartwood susceptible for
  longer periods.

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Modes of entrance for wood decay fungi

• c. Decayed stumps - sprouts from stumps can be
  affected by decay fungi from the old stump
• When possible, favor seedlings.
• Favor sprouts from small rather than large
  stumps. The will have less heartwood and less
  likelihood for decay.
• d. Sprout clumps
• There are two basic types of unions by which
  sprouts can be connected. ' Y' and 'U' unions.

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MYCORRHIZAE

• Not all fungi are detrimental. Some (a rather
  small group) form symbiotic relationships with
  the host roots. These are called "mycorrhizae" -
  literally, "fungus root". These generally form on
  feeder roots of higher plants.
• In mycorrhizae, there is a very strong
  interdependence (i.e., symbiosis) that exists
  between the fungus and the host. Most plants that
  generally form mycorrhizae do very poorly in
  their absence, and most mycorrhizal fungi are
  critically dependent on their hosts for survival
  - they generally are poor saprophytes, and they
  grow poorly if at all in culture.
• Mycorrhizal fungi are obligate parasites. So they
  must infect the host without killing it.

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MYCORRHIZAE

• Economics
• Mycorrhizae are very important. Establishment of
  most forests depends entirely on mycorrhizal
  formation. Orchids require them. Most agronomic
  crops (i.e., soybean) utilize them.
• Feeder roots
• These generally are sites of mycorrhizal
  formation. Remember characteristics of feeder
  roots
• 1. ephemeral (last only 1 season)
• 2. no secondary growth
• 3. no root cap
• Ex In conifers, 90-95 of roots are feeder
  roots, so you can see just how important these
  are.

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Classification

• There are two main types, based on the physical
  relationship between fungus and host root.
• 1. Endomycorrhizae - these often show no obvious
  morphological changes in root,
• 2. Ectomycorrhizae - these can induce a greatly
  modified root morphology.

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Classification

• 1. Endomycorrhizae - these often show no obvious
  morphological changes in root
• Mycelium is intracellular in the root cortex,
• Produced by both septate and non-septate
  (coenocytic) fungi.
• Septate - common fungus is Rhizoctonia. Septate
  fungi often produce mycorrhizae on Orchidaceous
  (Orchids) and Ericaceous (Arbutus. Azalea.
  Vaccinium) plants
• Aseptate - commonly in the Zygomycetes, family
  Endogonaceae. This group also is called
  vesicular-arbuscular (VA) mycorrhizal fungi.
• VA mycorrhizae are the most common type of
  mycorrhizae.
• They produce
• a) vesicles - large, swollen hyphae inside and
  outside cells. Used
• for storage
• b) arbuscules - branched haustoria inside cells.
  These allow fungi to steal nutrients from host
  without killing it and them.

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Classification

• Endomycorrhizae - these often show no obvious
  morphological changes in root
• Found on maple, sycamore, ash, gum, walnut,
  cypress, poplars, and some other conifers.
• This type also occurs on all agronomic crops,
  such as sorghum, corn, and grasses used as cover
  crops in tree nurseries.

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VAM Fungi
Overwinters, many, many years
vesicle
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Classification

• 2. Ectomycorrhizae - these can induce a greatly
  modified root morphology.

With
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Ectomycorrhizae on beech tree roots
Root covered withfungal sheath
Hyphae of sheath
X-section showing sheath
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Ectomycorrhizae

• Feeder roots surrounded by a thick layer of
  hyphae - the 'fungus mantle".
• Feeder roots permeated by network on
  intercellular hyphae in the cortex - the "Hartig
  net", named
• after Robert Hartig, the Father
• of Forest Pathology
• Found on pine, spruce, fir, beech,
• eucalyptus, alder, oak, and hickory
• Many diverse fungi can form ectomycorrhizae -
  Agaricales (gill fungi), many Ascomycetes,
  Imperfect Fungi, etc.
• Ectomycorrhizal associations can be very complex.
  As many as seven different fungi can be found on
  a single root system.

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What is the function (benefit) of mycorrhizae?

• (Many of these apply only to ectomycorrhizae)
• There are two main functions of mycorrhizae
• 1. Increased absorption
• a. Increased root surface area.
• b. Hyphae from mantle extend into soil, absorb,
  then conduct back to host roots.
• c. Selective absorption of certain elements.

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What is the function (benefit) of mycorrhizae?

• 2. Protection from root pathogens
• a. Fungi use as food the root exudates that
  normally would attract pathogens.
• b. Physical barrier to infection by pathogens.
• c. Fungi produce antibiotic substances that deter
  root pathogens.
• d. Alter the physical and chemical aspects of the
  rhizosphere so that microbial fauna are extremely
  diverse and hence antagonistic to root pathogens.
• e. Because they are parasites, their infection of
  host cells can stimulate production of
  host-produced compounds that are inhibitory to
  root pathogens. A form of induced, chemical
  resistance

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Ectomycorrhizae Thelephora terrestris
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Ectomycorrhizae

• Pisolithus tinctorius Control

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Ectomycorrhizae
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Ectomycorrhizae
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