AI path study cards

What is the microbiome?

The community of microorganisms that inhabit a particular environment.

Why is the microbiome important in forest pathology?

Microorganisms can interact with tree pathogens and influence whether diseases develop, spread, or are suppressed.

What is the epiphytic microbiome?

Microorganisms living on the surface of a plant.

What is the endophytic microbiome?

Microorganisms living inside plant tissues.

What is the phylloplane?

The surface of a plant's leaves.

What is the endophyllosphere?

The internal tissues of leaves where microorganisms can live.

What is the ectorhizosphere?

The soil region surrounding plant roots.

What is the rhizoplane?

The surface of plant roots.

What is the endorhizosphere?

The internal tissues of plant roots.

What is bulk soil?

Soil outside the immediate region influenced by plant roots.

What are fungal endophytes?

Fungi that colonize plant tissues and cause unapparent, asymptomatic infections.

Where can fungal endophytes be found?

Leaves, twigs, bark, and seeds.

What are three possible ecological roles of endophytes?

Dormant saprobes, latent pathogens, or mutualists.

What is a dormant saprobe?

An organism living in plant tissue that can obtain nutrients from dead organic material.

What is a latent pathogen?

A pathogen present in plant tissue that does not immediately cause visible disease.

What is a mutualist?

An organism that interacts with another organism in a way that benefits both.

What is antagonism?

Direct or indirect activity by one organism that suppresses the normal growth of another organism.

What are the four antagonistic mechanisms listed in the study guide?

Antibiosis, parasitism, competition, and hyphal interference.

What is antibiosis?

An interaction in which an organism produces substances that inhibit or suppress another organism.

What is an example of antibiosis involving bacteria?

Streptomyces produces streptomycin, which can inhibit other microorganisms.

Which fungus produces penicillin?

Penicillium.

Which bacterium produces pyrrolnitrin?

Burkholderia.

Which bacterium produces zwittermycin?

Bacillus.

Which bacterium produces phenazine?

Pseudomonas.

What is parasitism between microorganisms?

One organism lives at the expense of another organism.

What is hypovirulence?

A condition in which a pathogen becomes less harmful because it is infected by a virus.

What fungus is an example of hypovirulence?

Cryphonectria parasitica, the cause of chestnut blight.

How does the hypovirus affect Cryphonectria parasitica?

It weakens the fungus, allowing the tree's defenses to better limit the pathogen.

How is the hypovirus transmitted between fungi?

Through hyphal anastomosis between vegetatively compatible fungal strains.

Why has hypovirulence worked better in Europe than in the United States?

Greater fungal population variability in the United States limits vegetative compatibility and virus transmission.

What is competition between microorganisms?

Microorganisms compete for limited resources, space, or other conditions needed for growth.

How does wood moisture affect Geosmithia morbida?

Below 20% moisture it can sporulate and survive

Which fungi can outcompete Geosmithia morbida at higher wood moisture?

Trichoderma, Clonostachys, and Aspergillus.

What is hyphal interference?

Hyphae from different fungal species meet and one or both experience inhibition or death.

What is a hemiparasite?

A parasite that obtains water and nutrients from its host's xylem but is still photosynthetic.

What is a holoparasite?

A parasite that obtains carbon, nutrients, and water from its host and is non-photosynthetic or has greatly reduced photosynthesis.

What are haustoria?

Modified root structures produced by mistletoes that connect with host tissues and obtain resources.

Which mistletoe produces haustorial strands and sinkers?

Dwarf mistletoe, Arceuthobium.

What are haustorial strands and sinkers?

Structures that grow within host tissues and connect the mistletoe to the host's vascular system.

What is an example of a leafy mistletoe?

Phoradendron.

Is Phoradendron a hemiparasite or holoparasite?

A hemiparasite.

What are the main hosts of Phoradendron?

Mostly hardwood trees.

How is leafy mistletoe dispersed?

Birds disperse its seeds.

What is the general impact of leafy mistletoe on its host?

host impact is minor.

What is an example of dwarf mistletoe?

Arceuthobium.

Is Arceuthobium a hemiparasite or holoparasite?

A holoparasite.

What are the main hosts of dwarf mistletoe?

Conifers

Where does dwarf mistletoe grow on its host?

Mostly on the inner bark.

How are dwarf mistletoe seeds dispersed?

Sticky seeds are forcibly discharged and can stick to host needles.

What are common symptoms of dwarf mistletoe?

Stem swelling, witches' brooms, crown deterioration, needle chlorosis, reduced growth, and reduced cone production.

What is a witches' broom?

A dense abnormal cluster of branches caused by dwarf mistletoe infection.

What are possible impacts of severe dwarf mistletoe infection?

Reduced tree growth, reduced cone production, crown decline, and increased susceptibility to secondary infections.

What is Viscum album?

European mistletoe, which was introduced into California around 1900.

What notable host-range information is given for Viscum album?

large host range of 25 species, including northern red oak.

What are the three main categories of root diseases?

Structural root rots, necrosis of feeder roots, and diseases of vascular tissues in roots.

Which organisms commonly cause structural root rots?

Basidiomycetes, including Armillaria and Heterobasidion.

Which organisms commonly cause feeder-root necrosis?

Oomycetes, such as Phytophthora.

Which organisms can cause diseases of vascular tissues in roots?

Ascomycetes, such as Ophiostoma.

What is a common stand pattern associated with root disease?

Circular or bullseye patterns of disease and tree mortality.

Why do structural root diseases often form expanding disease centers?

The pathogen spreads from infected roots to nearby trees, often through root contact or root grafts.

Which root diseases commonly spread through root grafts?

Structural root diseases, including Armillaria and Heterobasidion root diseases.

What pattern is more typical of Phytophthora root disease?

Less uniform disease within a stand, often associated with drainage patterns and wet areas.

Why is Phytophthora disease associated with drainage patterns?

Water movement and wet soil conditions influence the movement and spread of the pathogen.

What are general symptoms of root disease?

Crown thinning, chlorosis, loss of older needles, flat tops, declining crowns, and tree mortality.

What must you often do to confirm root rot?

Excavate and examine the roots because the damage may not be visible above ground.

What are common signs of root disease?

Reproductive structures such as mushrooms or conks, mycelial fans, and rhizomorphs.

What is Armillaria root disease also called?

Shoestring root rot.

What type of disease does Armillaria cause?

Structural root disease.

What types of trees can Armillaria affect?

Both conifers and hardwoods.

Which trees are often most affected by Armillaria?

Older and weaker trees.

What are three signs associated with Armillaria root disease?

Mushrooms, mycelial fans, and rhizomorphs.

What is a mycelial fan?

A fan-shaped mass of fungal mycelium found beneath the bark or near infected roots.

What are rhizomorphs?

Cord-like structures made of fungal hyphae that help the fungus spread through soil and between roots.

How does Armillaria spread?

Through rhizomorphs and contact between infected and healthy roots.

What is Heterobasidion root disease?

A structural root disease caused by fungi in the Heterobasidion group.

How does Heterobasidion initially infect many forest sites?

Basidiospores from conks land on and infect freshly cut stumps.

How does Heterobasidion spread from infected stumps?

Mycelium grows from infected stumps into roots and can spread to healthy trees through root grafts.

What conditions favor Heterobasidion root disease?

dry sites

What are management approaches for Heterobasidion?

Treat stumps with borax or urea, apply Phlebiopsis gigantea as a biological control, and manage stand density.

What is Phlebiopsis gigantea used for?

Biological control on stumps to help prevent Heterobasidion infection.

What is Phellinus weirii also called?

Laminated root rot

What trees can be affected by laminated root rot?

Pines and firs, also showing infection in mountain hemlock.

What is the main feature of laminated root rot?

It causes a laminated decay of infected roots.

What is Phytophthora?

A group of oomycetes that cause important diseases of forest trees and other plants.

What type of root disease can Phytophthora cause?

Necrosis of feeder roots.

What environmental conditions are important for Phytophthora diseases?

Wet conditions and water movement are important for disease development and spread.

What are two Phytophthora diseases listed on the study guide?

Little leaf disease caused by P. cinnamomi and Port-Orford-cedar disease caused by P. lateralis.

Can Phytophthora generally be eradicated once a site is infected?

It cannot currently be eradicated once a site becomes infected.

What are general management approaches for Phytophthora?

Hygiene, quarantine, prevention of new introductions, and careful management of contaminated soil and plant material.

What is a canker?

A localized area of dead or damaged tissue on a woody plant, commonly involving the bark and living tissues beneath it.

Which tree tissues are especially affected by canker pathogens?

The phloem and cambium.

What does the phloem do?

It transports sugars and other materials through the tree.

What does the cambium do?

It produces new xylem and phloem, allowing the tree to grow in diameter.

How do canker pathogens commonly enter trees?

Through wounds.

How do canker pathogens often kill living host cells?

They commonly produce toxins that kill living cells.

What are the two main categories of cankers?

Annual cankers and perennial cankers.

What is an annual canker?

A canker that attacks for one season, after which the tree stops the invasion and forms callus over the dead tissue.

What is an example of an annual canker?

Caliciopsis canker caused by Caliciopsis pinea.

Which tree does Caliciopsis pinea infect?

Eastern white pine.

What is a perennial canker?

A canker that continues developing over multiple years.