Pathology

Forest Pathology

study of biotic and abiotic agents affecting the health of forest trees

study of Tree diseases

predicting and preventing/mininizing damage done

Disease

deviation in the "normal" functioning of a plant cause by some persistent agent

Localized disease

one part of the plant

Systemic disease

effects the entire plants

Effects of a disease

Reduced growth
Death
Loss of quality

Pathogen

Any agent that causes a disease:
Fungi, Virus, Bacteria...

Signs

The physical appearance of the pathogen: spores, woody conk, mycelium

Symptoms

appearance of the host due to the presence of a disease: gal, canker, red flagging

Virulence

ability to cause a disease

Disease Triangle

Pathogen
Environment
Host

Disease Tetrahedron

Pathogen
Environment
Host
Time

Pathogen

total of virulence, abundance, etc

Environment

Total of conditions favouring disease

Host

total of conditions favouring susceptibility

Time

success of pathogen influenced by time

Parasite

organism which grows on or in another living species that derives part of its food from that organism (host)

Obligate saprophyte

Organism that can only grow on dead organic matter (Decay Fungi)

Facultative parasite

Organism that is typically saprophytic, but under certain conditions may be parasitic (Decay Fungi in living trees)

Facultative saprophytes

Organisms that are typically parasites, but may be saprophytes under certain conditions (Some root disease)

Obligate parasite

Organisms that can only grow on living hosts, incapable of existing independent of living tissue (Rust fungi)

Commensalism

Symbiotic relationship where one organism benefits, without affecting the other

Mutualism

Relationship between two organisms where both organisms benefit

Parasitism

Non-mutualrelationship between organisms where an organism one species benefits at the expense of another organism of another species

Saprophytism

Chemoheterotrophic extra cellular digestion of dead or decayed organic matter

Symptoms of disease

Necrosis
Hypertrophy
Atrophy
Other Physiological responses

Necrosis

death of tissue or cells

Hypertophy

overgrowth of its or organs

Atrophy

reduced development or growth of tissue or organs

Other Physiological Responses

Resinosus

Casual Agents

Abiotic and Biotic agents

Abiotic agents

temperature extremes
soil conditions
air pollution
mechanical injuries
animal damage
fire

Biotic

fungal
bacterial
viral
nematode

Role of Fungi

Pathogens
Sparobes
Symbionts

Pathogens

organism that cause disease

Saprobes

decomposers

Symbionts

mutually beneficial relationship

Eukaryotic

posses membrane-bound nuclei and a range of cytoplasmic organelles

Hyphae

microscopic filaments, exhibit apical growth

Mycelium

network of hyphae

Chitin and Glucans

rigid cell wall

Septate

Hyphae with cross walls and one nuclei

Aseptate

Hyphae with no cross walls and many nuclei

Unicellular fungi

Yeast

Spores

sexual and asexual reproductive cell

Achlorophyllus

lack chlorophyll pigments

Chemoheterotrophic

require pre-existing sources of organic carbon and energy from chemical reactions to synthesize organic compounds for growth and energy

Fungi growth requirments

water
mineral nutrients
energy source
oxygen
protection from UV

Nutrient absorption

Small nutrient molecules
Big nutrient molecules

Small molecules

absorb directly across fungal wall

Big molecules

broken down via enzymatic breakdown

Enzymatic breakdown

secretion of enzymes to break down substrate to be diffused into hyphae

Sporulation

ensure a small portion of the fungus' protoplasm is widely and efficiently dispersed

Sporulation functions

Dispersal
Survival
Genetic variation

Teleomorph

Sexual, perfect or meiotic state

Anamorph

Asexual, imperfect or mitotic state

Disease causing families

Oomycetes
Ascomycetes
Zygomycetes
Basidiomycetes

Oomycetes

Zoospores (Asex) motile
Oospores (Sex) imobile
Oogonia

Oogonia

structure containing the female gametes

Zygomycetes

Zygospores (Sex)

Ascomycetes

Ascospore (Sex)
Conidia (Asex)
Hook (crozier) formation

Ascocarp

fruiting body where Ascospores are formed

Basidiomycetes

Basidia (Sex)
Conidia (Asex)
Hyphal clamp connections

Basidiocarp

fruiting body of basidiomycetes

basidium

compartment supporting the sterigmata and basidiospores

Host factors

Immune
Susceptible
Resistant

Immune

cannot be infected

Susceptible

can be infected

Resistant

may or may not be infected, and is the plant able to prevent the pathogen from killing it

Pathogen factors

Amount of inoculum
pathogen genetics
virulence of pathogen
type of reproduction
ecology and mode of spread

Pathogen reproduction

Monocyclic - having one reproductive cycle per growing season
Polycyclic - many reproductive cycles within one growing season

Environmental factors

moisture
temperature
Effect of human practices

Disease development

Dispersal
Penetration and Infection
Invasion and Colonization
Growth and Production
Dissemination
Survival

Dispersal

Wind, Water, Insects

Penetration and Infection

Inoculation, Primary and Secondary inoculum

Inoculation

initial contact of pathogen with site on a plant where infection is possible

Primary inoculum

survives dormancy in winter or summer and causes primary infections in the spring

Secondary inoculum

causes secondary infections

Invasion and Colonization

External contact
Direct injection to host

External Contact

Attach to host before penetration

Direct injection

Pathogens such as viruses, some bacteria placed directly into cells by their vectors

Invasion and Colonization of Host

Spore Germination
Germ tube and Appressorium development

Spore gemination

stimulated by contact with host surface, hydration, and chemical reactions

Germ tube and Appressorium development

tube locates stomata
penetration peg forces way into stomata
Haustorium form

Haustorium

branched projections of off hyphae into host cells that acts as an absorbing organ

Incubation interval

time between inoculation and appearance of disease symptoms

localized Invasion

infects one part of the plant

Systemic invasion

infects the entire plant

Dissemination

wind, rain, insects, irrigation, animals, tools

Pathogen survival

Overwinter/oversummer: on alternate host while primary host species is not growing

Dwarf Mistletoe

Arceuthobium

DM effects

reduced growth
decreased strength
Mortality of small trees
influence stand dynamics

Viscin

sticky substance covering DM seeds