PLSC EXAM TWO (final rendition)

Oomycetes, Myxomycetes, and Plasmodiophoromycetes.

What are the three main fungus-like groups of plant pathogens?

Sexual: ascospores; asexual: conidia (conidiospores).

What are the sexual and asexual spores of Ascomycetes?

A sac-like structure in which sexual ascospores are produced.

What is an ascus (plural asci)?

A specialized hyphal structure or stalk that produces asexual conidia.

What is a conidiophore?

An asexual structure that contains conidiophores and conidia.

What is a conidioma (plural conidiomata)?

Sexual ascospores

What spores does an apothecium produce, and are they sexual or asexual?

Sexual ascospores

What spores does a chasmothecium produce, and are they sexual or asexual?

Sexual ascospores

What spores does a perithecium produce, and are they sexual or asexual?

Asexual conidia

What spores does a synnema produce, and are they sexual or asexual?

Asexual conidia

What spores does an acervulus produce, and are they sexual or asexual?

Asexual conidia

What spores does a pycnidium produce, and are they sexual or asexual?

Apple scab infects apple trees; grape powdery mildew infects grapevines.

Which hosts are affected by apple scab and grape powdery mildew?

A hyphal bridge that helps distribute one nucleus of each mating type during division, maintaining dikaryotic cells.

What is a clamp connection in Basidiomycetes?

Sexual spores produces by the basidium.

What are basidiospores, also called sporidia in some plant pathogens?

It completes its life cycle on one host species, rather than requiring two unrelated host species.

What does autoecious mean for a rust fungus?

Teliospores: thick-walled survival spores formed in telia.

Which spore type is the principal overwintering spore of rust fungi?

Sexual spores produced by pycnia

What are pycniospores (spermatia) in rust fungi?

Asexual spores produced by aecia

What are aeciospores in rust fungi?

Asexual repeating spores produced by uredinia; responsible for secondary infection cycles.

What are urediniospores in rust fungi?

Sexual Teliospores

What does a telium produce?

Rust fungi are obligate parasites; many smut fungi can be facultative saprophytes.

Which basidiomycete pathogens are obligate parasites, and which can be facultative saprophytes?

Loose smut of wheat is typically monocyclic; wheat leaf rust is polycyclic.

Give one monocyclic and one polycyclic basidiomycete disease.

A Zygomycetes thick walled sexual spore

What is a zygospore?

A Zygomycetes structure that produces asexual spores

What is a sporangium?

Motile asexual zoospores, typically with a single posterior flagellum.

What type of spores do Chytridiomycetes produce?

Non-septate

What type of mycelium do Zygomycetes usually have?

Sexual: zygospores; asexual: sporangiospores.

What are the sexual and asexual spores of Zygomycetes?

Chytridiomycetes

Which plant-pathogenic fungal group includes species that develop inside host cells?

A thick-walled sexual resting spore produced by Oomycetes.

What is an oospore?

Coenocytic (Nonseptate)

What kind of hyphae do Oomycetes usually have?

Sexual: oospores; asexual: zoospores

What are the sexual and asexual spores of Oomycetes?

Late blight of potato and grape downy mildew.

Name two plant diseases caused by Oomycetes.

Its plasmodium explores routes and adjusts its growth and cytoplasmic flow in response to chemical cues and food sources.

How can a slime mold solve a maze without a brain?

1. protection - fungicides. 2. eradication - destroying crop residue. 3. resistance - using resistant seed hybrids. 4. exclusion - disease-free seed

What are four broad fungal disease-management categories, with examples?

Exclusion keeps a pathogen from entering; eradication removes or reduces inoculum already present.

How do exclusion and eradication differ in disease management?

Unsegmented roundworms; they belong to Kingdom Animalia.

What are nematodes, and what kingdom are they in?

Juvenile.

What does the J stand for in nematode life-cycle stages J1–J4?

Four juvenile stages (J1–J4) and four molts before adulthood.

How many juvenile stages and molts occur in a typical nematode life cycle?

Egg (first molt) → first-stage juvenile → second-stage juvenile → third-stage juvenile → fourth-stage juvenile → adult

What is the typical nematode life-cycle sequence, written out?

Slender and worm-shaped. (vermiform)

What is the usual shape of an adult male soybean cyst nematode?

Vermiform (wormlike), pear-shaped or lemon-shaped.

What are the main body shapes seen among plant-parasitic nematodes?

A nematode that remains outside plant tissue while feeding on cells with its stylet.

What is an ectoparasitic nematode?

Stunting, chlorosis, wilting, and reduced yield.

What above ground symptoms can plant-parasitic nematodes cause?

Root galls, lesions or necrosis, deformed roots, and reduced root systems.

What belowground symptoms can plant-parasitic nematodes cause?

Endoparasitic

Are cyst, root-knot, and lesion nematodes endoparasitic or ectoparasitic?

multinucleate root feeding cells

What are the giant cells induced by root-knot nematodes?

Root-knot nematodes (Meloidogyne spp.)

Which nematodes induce giant cells versus syncytia?

Infested soil moved on equipment, irrigation/flood water, and infected planting material.

Name three common ways nematodes are dispersed between fields.

In resistant eggs or cysts, or by entering dormancy (cryptobiosis.)

How can plant-parasitic nematodes survive unfavorable conditions?

Visible woollike masses of dormant stem-and-bulb nematodes

What is nema wool?

Heterodera glycines.

What is the scientific name of soybean cyst nematode (SCN)?

Soybean is primary host but can be found on other legumes and weeds

What are important host plants of soybean cyst nematode?

Stunting, chlorosis, reduced vigor/yield, and poorly developed roots

What symptoms can soybean cyst nematode cause in soybeans?

Young females are whitish to yellow; after death, their bodies harden and darken to brown

Why are some soybean cyst nematode females pale yellow while others become brown?

Exclusion: clean machinery; Cultural control: nonhost rotation; protection: labeled nematicide; resistance: SCN-resistant soybean.

Give four disease-management categories with nematode examples.

Bacteria that lack a rigid cell wall; phytoplasmas and spiroplasmas

What are mollicutes and what are two examples

A long, filamentous appendage used for movement.

What is a bacterial flagellum?

Bacteria lack a membrane-bound nucleus and membrane-bound organelles; eukaryotic cells possess them.

How do prokaryotic bacterial cells differ from eukaryotic cells?

Cocci, bacilli, and spiral forms.

What are the three basic shapes of walled bacteria?

A bacterium with a thick peptidoglycan wall that stains purple.

What does Gram-positive mean?

A bacterium with a thin peptidoglycan layer that stains pink/red

What does Gram-negative mean?

Maintains cell shape and helps protect against osmotic rupture.

What is the function of the bacterial cell wall?

Controls what enters and leaves the cell and supports important metabolic processes.

What is the function of the bacterial cell membrane?

The non-membrane-bound region containing the bacteria’s chromosomal DNA.

What is the nucleoid in a bacterial cell?

Make proteins (protein synthesis).

What do bacterial ribosomes do?

Appendages used for attachment or DNA transfer.

What are pili or fimbriae on bacteria?

Through natural openings (such as stomata or hydathodes) or through wounds.

How do plant-pathogenic bacteria typically enter plants?

In intercellular spaces or in xylem vessels.

Where can plant-pathogenic bacteria live within plant tissues?

By signs/symptoms or Gram stain tests

How can a suspected plant-pathogenic bacterium be identified?

Pseudomonas, Xanthomonas, and Erwinia.

Name three bacterial genera that cause plant diseases.

Exclusion: pathogen-free plants; eradication: remove infected plants; protection: copper treatment; resistance: resistant cultivar.

Give four disease-management categories with bacterial examples.

Common rust causes darker elongated pustules on both leaf surfaces; southern rust: small bright-orange pustules on the upper surface.

How do common rust and southern rust of corn differ in pustule appearance?

Common rust: Puccinia sorghi; southern rust: Puccinia polysora.

Which fungi cause common rust versus southern rust of corn?

Fusarium ear rot produces fumonisins

Give one corn ear rot disease and a mycotoxin it produces.

Extracellular polysaccharide (EPS)

Slime layer or capsule attached to the exterior surface of many bacterial cells

Rusts

Basidiomycete fungi with a polycyclic disease cycle.

Plasmodium

A mass of cytoplasm containing many nuclei but no cell wall.

Coccal

Bacteria that are round or spherical in shape.

Phytoplasmas

Bacteria without cell walls; pleiomorphic or variably shaped.

Capsid

Protein coat that surrounds a virus particle.

Bacilliform

Rod-shaped bacteria.

Smuts

Basidiomycete fungi with a monocyclic disease cycle.

Spiroplasmas

Bacteria without cell walls; usually helical in shape.

Meloidogyne spp.

Root-knot nematodes.

Pratylenchus spp.

Lesion nematodes genera name

Heterodera spp.

Cyst nematodes genus name

Parthenogenetic

Reproduction from an unfertilized egg (no male fertilization).

Sclerotium

A compact, hardened mass of fungal hyphae that survives unfavorable conditions and later germinates.

Heteroecious

A pathogen (often a rust) requiring two unrelated host species to complete its life cycle.

Disease complex

Disease caused or intensified by the interaction of two or more pathogens, rather than a single pathogen acting alone.

Syncytium

A multinucleate feeding site formed when neighboring root cells fuse; induced by cyst nematodes.

1. Rain, irrigation, or runoff. 2. Insect Vectors 3. Contaminated tools/equipment.

List three ways that bacteria are disseminated.

Bacterial ooze

What is a sign that indicates the presence of bacteria in a plant?

1. Suspected pathogen is consistently associated with diseased plants; 2. Isolate the pathogen and obtain it in pure culture; 3. Inoculate a healthy susceptible plant and reproduce the disease; 4. Re-isolate the same pathogen from the newly diseased plant.

What are the four Koch’s Postulates for proof of pathogenicity?

1. Necrosis; 2. Wilting; 3. Soft rot; 4. Blight (or cankers / galls).

Name four plant symptoms caused by bacteria.

1. Ascomycetes; 2. Basidiomycetes; 3. Zygomycetes; 4. Chytridiomycetes.

What are the four main groups of plant pathogenic fungi?

1. Protection: apply a fungicide before infection 2. Eradication: destroy infected crop residue

Name two general control methods for plant-pathogenic fungi and give a specific example for each.