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

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'.

Mushrooms

Characteristics of wood decaya. 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.

Characteristics of wood decaye. 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 100Note: If wood is saturated, decay will not occur even though moisture >

FSP. This is due to anaerobic conditions in wood.

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.

Shoestring Root Rot

Root Rot of TreesEx. of White Rot

Rhizomorphs of Armillaria sp.

adhering to roots of apple

• 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.

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/2003/03/030327074535.htm

Modes of entrance for wood decay fungi

a. Woundsi. Fire - a major infection court. Causes typical wound,

called a 'cat face'.ii. Logging wounds - severity depends on size and depth of

wound. There is direct relationship between wound size and time required for healing. Anything > 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.

iii. Blazing - with an axe. USE PAINT!! iv. Storms - damage due to wind, ice, etc. Conifers more

resistant than hardwoods, due to tree architecture.

Modes of entrance for wood decay fungi

a. Wounds

v. Cankers - some diseases cause cankers on tree trunks and branches. If these expose heartwood, then decay organisms can become established.

vi. 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.

vii. Insects - bore holes in wood and expose heartwood..

Modes of entrance for wood decay fungi

b. Branch stubs - many folks do not know how to prune.

i. Prune only branches < 3" in diameter. This prevents heartwood from being exposed

ii. Prune such that natural healing is promoted.iii. DO NOT use wound dressings. They serve only

to trap moisture and make heartwood susceptible for longer periods.

Modes of entrance for wood decay fungi

c. Decayed stumps - sprouts from stumps can be affected by decay fungi from the old stump

i. When possible, favor seedlings.ii. Favor sprouts from small rather than large

stumps. The will have less heartwood and less likelihood for decay.

d. Sprout clumpsThere are two basic types of unions by which

sprouts can be connected. ' Y' and 'U' unions.

MYCORRHIZAENot 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.

MYCORRHIZAEEconomicsMycorrhizae are very important. Establishment of most

forests depends entirely on mycorrhizal formation. Orchids require them. Most agronomic crops (i.e., soybean) utilize them.

Feeder rootsThese generally are sites of mycorrhizal formation.

Remember characteristics of feeder roots:1. ephemeral (last only 1 season)2. no secondary growth3. no root capEx: In conifers, 90-95% of roots are feeder roots, so you can

see just how important these are.

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.

Classification1. Endomycorrhizae - these often show no obvious morphological changes in root

a. Mycelium is intracellular in the root cortex, b. Produced by both septate and non-septate (coenocytic) fungi.

i. Septate - common fungus is Rhizoctonia. Septate fungi often produce mycorrhizae on Orchidaceous (Orchids) and Ericaceous (Arbutus. Azalea. Vaccinium) plants

ii. 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.

Classification

1. 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.

VAM Fungi

vesicle

Overwinters, many, many years

Classification2. Ectomycorrhizae - these can induce a greatly

modified root morphology.With

Ectomycorrhizae on beech tree roots

Root covered with

fungal sheath

X-section showing sheath

Hyphae of sheath

EctomycorrhizaeFeeder 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.

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.

What is the function (benefit) of mycorrhizae?

2. Protection from root pathogensa. 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…

Ectomycorrhizae Thelephora terrestris

Ectomycorrhizae

• Pisolithus tinctorius Control

Ectomycorrhizae

Ectomycorrhizae