Plant Pathology Exam 1

Oomycetes

Oomycetes differ from “true fungi” T/F

T

How do oomycetes differ from '“true fungi”

Lacks septa

Longer strands of filaments

Sporangia characteristics (6)

1. Primary/secondary inoculum

2. Asexual

3. Diploid

4. Short-lived

5. Wind or water dispersal

   1. Produce zoospores or direct germination

6. Requires water for germination

Draw a zoospore

Name 4 zoospore characteristics

1. Short-lived

2. Asexual

3. Diploid

4. Biflagellate motile spore

Chemotaxis

Movement or growth in response to changing concentration of a chemical stimulus

Name the structure in the picture

Gamatangia

Homothalic (repro-gamatangia)

Self-compatible

No mating type required for fertilization

Heterothalic (repro-gamatangia)

Self-incompatible

Opposite mating type required for fertilization

Name one advantage & disadvantage of heterothlism in fungal pathogens

Adv. genetic variation

Dis. both mating types aren’t always present in certain regions

What is the potato blight pathogen?

Phytophora infestans

What are the ideal conditions for potato blight?

Greater than 90% humidity

Warm days, cool nights w/ extended wet conditions

Sporangia produced 64-72F optimum

Symptoms of potato blight

Water soaked lesions (purple-grey white hue around edges of leaves)

Blighting

Purple/darker coloring on tuber

Signs of potato blight

Sporulation on underside of leaves

What conditions would lead to greater late blight epidemic?

Warm days & cool nights 60-70F

Cool nights enable induction & zoospore production so more potential for infection

How to manage late blight?

Exclusion: pathogen free tubers

Avoidance: site selection- air movement, good drainage

Eradication: crop rotation

Protection: resistant varieties

What is the pathogen of Downy Mildew of Grape called?

Plasmopara viticola

What are the ideal conditions for downy mildew of grape?

Oospores germinate 10-10-10 (cm of new growth, degrees, rainfall)

64-76F

High humidity

Symptoms of downy mildew of grape

Round light chlorotic spots

Fruit-rot like symptoms on grapes

Signs of Downy Mildew of Grape

Sporangia on sporangiophores

Underside of leaf

Disease management for downy mildew of grape

Row spacing- more air flow

Resistant varieties

What pathogen causes seedling damping-off?

Pythium spp.

Phytopthora

What are the idea conditions for seedling damping off?

Wet, soil conditions

Symptoms of seedling dampening off

Root rot

Reduced vigor

Death

Disease management for seedling dampening off

1. Soil sterilization

2. Improve soil drainage

3. Composted pine bark media

4. Fungicide seed treatment (MOST COMMON)

What are the 4 characteristics of fungi?

1. Eukaryotic

2. Heterotrophic: digest then ingest

3. Vegetative stage: filaments

4. Spores: survival/dissemination

What are the growth conditions for fungi?

Can grow on any carbon source

Moist environments

Food source: decomposers (saprophytes), parasites, mutualists

Large temp range

Light not required except for repro

pH: 5-6

Hypha

Single filament

Basic unit of structure & function

Can designate hyphae to different functions: fruiting, feeding, growing

Energy at tips

Mycelium

Network of hyphae

Made of chitin

Rapid, indeterminant growth in apical fashion

Hyphal tip

Zone of nutrient acquisition

How are spores produced & what are their purposes?

Mitosis or meiosis

Dispersal & survival

What allows spores to remain dormant?

Low water content & low metabolic activity

What features do spores have that promote long-term survival?

Thick cell walls

Dark pigmentation

Chemical adaptations

When are short lived spores produced?

In secondary disease cycles

Holomorph

All forms of a fungus, latent or expressed

Anamorph

Asexual forms of a fungi

Telemorph

Sexual forms

Obligate parasite

Always a parasite, ca only live in a living host

Ex. powdery mildew, viruses, rust

Facultative saprophyte

Usually a parasite but can live on dead/decaying tissue under right conditions

Ex. Pythoptera

Facultative parasite

Saporophyte but can parasitize & cause disease under right conditions

Ex. Pythium

Obligate Saprophyte

Only live on decaying matter

Ex. Beer, bread & wine yeast

List one step in the interaction between the pathogen & the host that occurs in the development of disease

The growth of pathogen on host

Pathogen taking energy from host to reproduce

Draw a polycyclic disease cycle

Inoculum

Pathogen or its parts that cause infection

Inoculation

Pathogen coming in contact w/ a plant host

Where might a pathogen enter a plant?

Stomata

Cuticle

Wounds

How might a pathogen penetrate a host?

They may pierce plant tissue or use enzymes to digest cell walls

Describe penetration via forceful apperessoria

A specialized structure uses pressure using water due to the GLYCEROL which pulls water into the apperesorium

Describe chemical assisted penetration

The apperasorium attaches to the plant and absorbs the broken down cuticle to create more cutinase gene which macerates the cuticle and allows fungus to enter

Colonization

Pathogen overcoming host’s defenses

Beginning to establish feeding habits

Name the step in the disease cycle that is described
A spore produces an appressorium to penetrate the host cuticle

Infection

Name the step in the disease cycle that is described

Spores are produced on recently colonized foliage during optimal conditions for pathogen growth

Production of secondary inoculum

Disease management: Avoidance

Minimize or avoid inolculation

Ex. field selection, planning where to plant host, timing

Disease management: Exclusion

Limit dispersal of pathogen in area

Ex. Quarentine & regulation laws, pathogen free seed/stock

Disease management: Eradication

Reduce SURVIVAL of an established pathogen in area

Ex. Soil sterilization, crop rotation

Disease management: Protection

Measures aimed at reducing pathogen infection of host

Ex. Using resistant varieties, biological control, chemical control

Disease progress curve

Amount of disease plotted as a function of time

What is the best way to manage a monocyclic disease?

Reduce primary inoculum, sanitation, crop rotation

What is the best way to manage a polycyclic disease?

Resistant varieties, proper row spacing, fungicides

Plant disease

A detrimental alteration in the physiological or morphological development of a plant in response to continuous exposre to a pathogen

Injury

Instantaneous damage to a plant which inhibits growth

Pathogen

An infectious agent or microorganism that can cause disease in its host

Parasitism

Detrimental to host

Mutualism

Mutually beneficial

Commensalism

Unilaterally beneficial

Pathogenicity

Ability of organism to cause disease

Virulence

Degree to which an organism may cause disease

3 Aspects of Disease Triangle

1. Host

2. Pathogen'

3. Environment

What is resistance influenced by?

Genetics & environment

Draw a monocyclic disease cycle