EFB 340: Forest Path Exam 1

Disease

Chronic disruption of the structure or function of host tissues. Persistent association between pathogen and host

Pathogen

A biological organism (parasite) that causes disease. Infectious (virulent), Penetrates tissues and causes infection, spreadable, Biotic

Disease Triangle

- host

- pathogen

- environment

Signs

Physical presence of or structures made by the organism

Symptoms

Observed effects on the plant that disrupt its normal function

Necrotroph

Kill all or part of their host before consuming it (damping-off, cankers,wilts, leaf-spots). facultative

Biotroph

Complete life cycle only on living hosts(rusts, downy mildews,powdery mildews). obligate

Kochs Postulates

1. Establish consistent association of disease organism and disease symptoms

2. Isolate organism and grow in pure culture

3. Inoculate healthy plant and produce disease symptoms

4. Re-isolate organism

Fungi (functional definition)

- Assimilative (i.e., endo-) chemoheterotroph

- Microbe

Fungi (taxonomic definition)

- Estimated: (0.6-) 2.5 - 3.8 (-1000) M spp.

- Described: ~150 K spp.

Phyla:

- Ascomycota

- Basidiomycota

- Glomeromycota

- Chytridiomycota

- Zygomycota

Fungal nuclear states

- Monokaryotic

- Dikaryotic

Host

Susceptibility: capacity to become infected• Resistance: capacity to resist infection• Tolerance: capacity to become infected to the same extent as susceptible individuals, but the visible or quantifiable effect of disease is negligible

Host --> Pathogen

Determined by genetics of host and pathogen

Symbiosis

Two different kinds of organisms living together in an intimate relationship. Symbiosis does NOT mean mutually beneficial

Physiological Disorder

Non-infectious, Abiotic, initially, Chronic physiological disorders often lead to disease

Major Pathogen groups

- Viruses

- Phytoplasmas

- Bacteria

- Fungi

- Nematodes

- Parasitic plants

Saprotrophs

Consume dead organic matter only.(heart rots, sooty molds)

Hemibiotrophs

Have both a biotrophic and necrotrophic phase

Symptoms examples

- discoloration

- necrosis

- galls

- stunting

- wilting

- defoliation

Substrate

Host or materialfungus is growing in

How do fungus eat

Absorptive Nutrition Osmotic Heterotrophs

Hyphae

long, branching, thread-like filaments that make up the main structural body of most fungi

Coenocytic hyphae

- No septa

- Some fungi and all oomycetes

Plant cell wall is made of

cellulose

Fungal cell walls

Totipotent

Mycelium

network of hyphae

Yeasts

single-celled fungi (not hyphal)

Chemotropism

Growth navigated by chemical stimulus

Homokaryotic

- Same type of nucleus within each cell of the hypha

- Each is the same haplotype, the same genotype coming from the same parent

Anastomosis

Two hyphae fuse their cell walls and plasma membranes

Plasmogamy

Mixing of the cytoplasms of two separate hyphae. Plasmogamy is a consequence of anastomosis.

Karyogamy

Fusion of two haploid nuclei to create a diploid nucleus

Ascomycota

Ascus/asci in ascoma

Basidiomycota

Basidium/basidia in basidioma

Ascospores

8 spores per ascus

types of asci

- Prototunicate (disintegration)

- Operculate ("hat")

- Inoperculate (pore)

- Bitunicate (double walled)

Meiospores

- Ascospore

- Basidiospore

- Oospore

Mitospores

- Conidium

- Zoospores

- Chlamydospore

Types of Ascoma

- Apothecia (open)

- Perithecia (pore opens at maturity)

- Chasmothecia/Cleistothecia (closed)

- Ascostroma (embedded in a stroma)

Pseudothecia

Like perithecia, but ascoma develops before anastomosis/plasmogamy

Anamorph vs teleomorph

- Anamorph (asexual phase, producing conidia on conidiophores)

- Teleomorph (sexual phase, meiospores)

Basidiomycetes vs Ascomycetes

Ascomycetes: have asci and hold 8 ascospores

Basidiomycetes: have a basidium and hold 4 basidiospores

Oomycetes

-Eukaryotic

-Heterotrophic (absorptive nutrition)

- Cellulose in cell walls

- Motile asexual zoospores (swimmers)

- Most of life cycle with diploid (2N) nuclei

- Truly coenocytic (no true septa)

- Sexual and asexual reproduction by spores

Oomycetes spore type

Oospore

Benefits of Decay in the Forest

- Carbon and nutrient cycling

- Facilitates forest succession & tree species composition

- Removes less fit genotypes

- Biodiversity: decaying trees provide homes to innumerable microbes, insects, and fungi

- Wildlife habitat

Wood

Accumulated xylem tissue of plants with a secondary vascular cambium (contains lignin)

Xylem

Vascular tissue of plants that conducts water and nutrients upward from the roots.

Outer bark

Dead cells that provide physical protection for the tree

Phloem

(inner bark) is living cells that transports sugars (phloem sap)down from leaves

Cambium

Is a meristem that produces secondary tissues - new xylem and phloem to allow radial growth

Sapwood

- Active conduction and storage (SAP moving up!)

- Contains dead (xylem) and living (parenchyma) cells

Heartwood

- Structural support only

- Contains dead (xylem) and dead (parenchyma) cells

- Heavily reinforced with lignin

Wood is composed of

- Lignin (15-25)

- Hemicellulose (20-30)

- Cellulose (45-55)

Cellulose

3 Glucose molecules joined by β(1,4) Glucan linkages

Hemicellulose

- Heteropolymer: polysaccharide consisting of multiple different monomers

- Branched chains of 500 - 3,000 monomers

- Amorphous and weak compared to cellulose

- But bonds with both cellulose and lignin

Lignin

- Polyphenolic heteropolymer

- 3 primary subunits possible

- Extremely difficult to degrade biologically

- Plants often increase lignin synthesis in response to pathogen invasion

Conifer

- (gymnosperm)

- Tracheid

- Parenchyma

- Resin ducts (absence of cells)

Hardwood

- (angiosperm)

- Ring-porous

- Diffuse-porous

- Vessel

- Fiber

- Parenchyma

- Tracheid

Ray Parenchyma Cells

Arrayed radially, perpendicular to growth rings

- Store water, starch, sugars and nutrients

- Allow movement of sugars and nutrients

- Can synthesize and extrude defensive chemicals

- Alive in sapwood

Parenchyma Cells

- Live at maturity

- Totipotent, can divide and develop into a complete plant

- Primary cell walls

- Large central vacuole

- Many shapes

- Photosynthesis, storage

How does Sapwood fight off Pathogens

Sapwood: Active

- Ray parenchyma and companion cells synthesize and extrude defensive chemicals

- Sapwood more prone to pathogens because living parenchyma stores water, starch, sugars and nutrients

How does Heartwood fight off Pathogens

Heartwood: Passive

- High lignin and extractive content protect against most pathogens

- Parenchyma plugs up xylem tissues with lignin and extractives before they die within the transition zone from sapwood to heartwood

Wood Decay

The continuum of changes in the physical & chemical properties of wood caused by the chemical activities of microorganisms.

Stub

- Protruding from stem

- Occurs when branches and tops break or die

- Delays wound closure and allows decay process to proceed for many years

Scars

Caused by removal or death of bark. Wounding serves as infection court

Fungal Wood Decay

- Hyphal tips enter the wood cell wall and lie where moisture is abundant

- Exoenzymes are produced and diffuse into the secondary cell wall

Stages of Decay

- Incipient (Stained, firm wood, but fungus is well established)

- Early

- Intermediate

- Advanced (Soft and easily penetrable)

Incipient

Prior to the linear phase of decay

Advanced

Approaching steady state for that substrate/organism

Detection

- Tree coring

- Resistograph

- Shigometers

- PiCUS Sonic Tomograph

- NOT conks

White Decay

- Basidiomycetes

- 1st Lignin & hemicellulose 2nd Cellulose

- Fibrous

- Can decay up to 97% of wood mass

- More common in both conifers and hardwoods

- Both living and dead trees

Brown Decay

- Basidiomycetes

- Cellulose & hemicellulose

- Cubical rot

- Brown, oxidized lignin left behind

- 70% Wood mass decayed

Soft Decay

- Ascomycetes

- 1st Cellulose & Hemicellulose 2nd Lignin

- Brittle, soft

Wood Decay Disease Cycle

- Airborne basidiospores

- Only a few produce conidia

- Enter through wounds or root grafts

- Very slow!! Less than 10 cm/yr

- More common in old trees

Management for Decay

- Silvicultural

- Proper pruning

- Removal

Types of plant defenses

- Constitutive (always present/expressed) e.g. physical barriers or wood chemistry

- Induced E.g., traumatic resin ducts in conifers, Defense "priming", Reaction zone

CODIT

Compartmentalization Of Decay In Trees

CODIT purpose

- Trees don't heal, they seal

- A series of four "walls" allow it to constrain the spread of an invading wood decay fungus

CODIT Model

- Wall 1: Vertical (weakest)

- Wall 2: Inner rings

- Wall 3: Rays

- Wall 4: Outer rings

How do Trees confine the spread of the decay? (CODIT walls)

- 1. Ends of vertically oriented vessels, prevent up and downward spread

- 2. Latewood of annual rings, prevent inward radial spread

- 3. Ray cells, prevent transverse spread

- 4. At the cambium, rich of defense compounds, prevent outward radial spread

CODIT: Wall 1

- Vessel elements and tracheids near fungus are plugged by: Tyloses & Gums (Polyphenolic secretions from cells, can be fungistatic)

- Induced defenses

- Weakest of 4 "walls"

- Slows vertical (longitudinal) fungal growth

Shoot & Leaf Blight

Impaired growth

Chlorosis

Photosynthesis

Leaf spots

Photosynthesis

Canker

Nutrient transport

Sap decay

Structural integrity & nutrient transport

Butt decay

Structural integrity

Root disease

Root extension

Gall

Nutrient transport

Heart decay

Structural integrity

Vascular wilt

Water transport

Seed Decay

Reproduction

Where do microbes live in the leaf

Haustorium

Infection Courts

- Natural opening

- Direct penetration

Biotrophic Pathogen (foliar)

- Powdery Mildew (Ascomycetes)

- Tar Spot of Mapple

Necrotrophic Pathogen (foliar)

- Sycamore Anthracnose

Biotrophs vs necrotrophs (foliar disease)

Biotrophs: obligate parasite, Narrow host range, kills host cells quickly

Necrotrophs: facultative parasite, broad host range, saprotrophic growth, kills host cells quickly

Foliar disease environmental factors

- Moisture triggers ascospore or conidia release, germination, and infection

- Leaf wetness period and temperature thresholds are also critical

- Disease is most serious when years are cool and wet

- Driven by stand and site factors

Foliar disease cycle

1. (Spring) Primary inoculum (often sexual stage) produced on dead leaves on the ground (sometimes twig lesions), becomes airborne, germinates on and infects newly emerging leaves

2. (Late Spring & Summer) Secondary inoculum (often asexual stage) produced on infected living leaves. Dispersed by water-splash orin air and infects more leaves

3. (Summer) If conditions are suitable, secondary inoculum continues to cause infections

4. (Fall) Infected leaves fall to ground, fungi overwinters

PRIMARY INOCULUM

- Present at the start of the epidemic

- Initiate primary infections