What is “plant pathology”? · History of plant pathology •Theophrastus (c. 300 B.C.): Greek...

10/31/2013

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Richard J Buckley, PDL Director

Soil Testing and Plant

Diagnostic Services

MG Training:

Basic plant

pathology and

the art of the

diagnosis.

www.njaes.rutgers.edu/services

What is “plant pathology”?

• Plant pathology is the study of:

– living entities and environmental

conditions that cause disease in plants

– mechanisms by which these factors result

in disease

– interactions between disease agents and

hosts

– disease prevention and management

History of plant pathology

• Theophrastus (c. 300 B.C.): Greek philosopher

who believed that God controlled the weather

and brought about disease; diseases were the

manifestation of the Wrath of God

• Concept of spontaneous generation: diseases

(human and plants) develop spontaneously

• Even after advent of the microscope, the

microbes observed were thought to be the

result of the disease, not the cause of it

History of plant pathology

• In 1845, late blight of

potato epidemics

occurred in Belgium,

Holland, Germany,

Switzerland, France,

Italy, England, Ireland,

and Scotland

• Completely destroyed

the potato crop in

Ireland in 1845-1846

(Irish potato famine)

Anton deBary: the father of plant pathology

• In controlled

experiments, proved

that a fungus causes

late blight (1861)

• Fungus was named

Phytophthora infestans

(Phyto = plant; phthora

= destroyer)

Anton deBary (APS)

Irish potato famine (1845-46)

• Gave birth to the science of plant pathology

• Changed the course of human history

• Introduces:

– The political aspects of the food supply

– Risks of genetic uniformity in crops

– Problems when new crops are distributed

throughout the world

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Plant Pathology 101

• Plant Disease:

–any disturbance of a plant that

interferes with its normal structure,

function, or economic value, or

–any condition of a plant that is

contrary to grower expectations

Plant Pathology 101

• Plant Disease: a condition of abnormal physiology in a

susceptible host plant that is a result of

the plants constant association with a

disease causing agent within a set of

favorable environmental conditions.

Plant Pathology 101

Host Plant Condition

• Most plants resist or tolerate attack

• Plant must be susceptible to attack

• Resistance and susceptibility different

degrees of the same thing

influenced by genetics

influenced by environment

• Immunity is absolute

Two types of causal agents:

1. Biotic (infectious)

– organism (pathogen) grows, multiplies,

and spreads to other plants

– 10% of diseases reported

2. Abiotic (non-infectious)

– environmental conditions that impact

plant development (physiogens)

– much more common: 90% of diseases

reported (injury not disease)

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Abiotic Causal Agents - Physiogens

• Physical factors

temperature

moisture

• Chemical factors

air pollutants

pesticides

fertilizers and salts

• Mechanical factors

everything else

Biotic Causal Agents - Pathogens

• Fungi (largest group of plant pathogens)

• Prokaryotes (no nuclear membrane)

– bacteria

– mollicutes (phytoplasmas, spiroplasmas)

• Nematodes (round worms)

• Viruses (nucleic acid with a protein coat)

• Viroids (naked RNA with no protein coat)

• Parasitic plants

• Algae

• Protozoa

• Insects and mites

Fungi

• Systematic study of fungi is 250 years old

• Mycology is Greek for mycos (fungus) + -logy (study of)

• Manifestations of this group of organisms is thousands

of years old (e.g., wine and leavened bread)

• Most important as agents of decay

• Can attack wood products, leather goods, fabrics,

petroleum products, foodstuffs

• Infect animals and plants: most common (or important)

of plant pathogens

Cottony mycelium of Pythium

Photo: APS Press

Pythium Disease Complex

Bacteria

• 1600 species are known, most are saprophytic

• Important as decomposers and in nitrogen recycling

• Cause human, animal (e.g., tuberculosis, pneumonia,

typhoid fever), and plant diseases

• Actinomycetes produce antibiotic compounds

• Shapes: rod, spherical (cocci), spiral, or filamentous

• Reproduce by fission (they divide in two)

Xylella fastidiosa - a single-celled bacterium with

rippled cell walls

Bacteria

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http://www.sciencenetlinks.com/images/interactive/bacteria.gif

Bacteriology 101

Bacteria are found in every ecological niche

Large colonies form a biofilm: an extracellular polysaccharide ooze

Bacteriology 101

Pathogenic bacteria are found on their hosts

Infection occurs through natural openings or wounds

Large populations overwhelm plant defenses and invade xylem tissues

Plant tissues are killed and digested by toxins and enzymes

Photo: APS PressIllustration by Samatha Bozak

Virus

• entity that contains genetic material within a protein coat

that can only reproduce using the metabolic processes of

a suitable host cell

– Structure

• Protein coat = capsid

• Nucleic acid core (DNA or RNA) = nucleocapsid

– Size

• Ultramicroscopic = too small for microscope

• Must use electron microscope

– Shape

• Rod, filamentous, isometric

• May have more than one particle – satellites

Tobacco Mosaic Virus

Photo: APS Press

Nematode

• Kingdom Animalia; non-segmented roundworms

• Several thousand species

• Most live in fresh or salt water, feeding on

microorganisms and microscopic plants and animals

• Numerous species attack animals

• Several hundred species feed on living plants (roots

or foliar tissue), obtaining food with stylets

• Annual losses on crops such as grains, legumes,

banana, cassava, coconut, potato, sugar beet,

sugarcane, and sweet potato are approximately 11%

Plant parasite

Plant parasitic nematodes have a stylet

Photo: Richard Buckley, NJAES

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Parasitic Plants

• Epiphyte – orchid, spanish moss

• Hemi parasite – mistletoe

• True parasite – dodder, witchweed, dwarf mistletoe

Biotic Causal Agents

dodderPhoto: Richard Buckley, NJAES

• Pathogen must be present

• Pathogen must be pathogenic

• Pathogen must be virulent

influenced by genetics

influenced by environment

Causal Agent

Photo: Dr. Peter Dernoeden, UMD

Environmental Condition

• Provides pathogen opportunities

influences host plant condition

increases pathogen virulence

• Predisposing conditions

site

weather

management

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Recognizing Diseases

• Symptoms -

observable condition of abnormal physiology in the plant

• Signs -

physical presence of the causal agent or clear evidence of abiotic stress factors

Symptom descriptions

leaf spot, blight, tip blight,

dieback, flagging, chlorosis,

necrosis, canker, wilt, root rot,

witches broom, mottling,

interveinal necrosis, epinasty,

scorch, crown rot, defoliation,

boring phyllody, leaf blotch, rust,

damping off, soft rot,

mummification, stem pitting, gall,

shot-hole, bleeding, slime flux,

blast, scald, bronzing, staghead,

tumefacation, fasciation, hairy

root, knots, enation, shoestring,

erinos, stipple, notching,

chewing, skeletonization, rugose,

puckering, edema, intumescence,

russet, scab, callus, leafroll, leaf

curl, croziers, dwarfing, stunting,

rosetting, atrophy, etiolation,

spiralism, hyperelongated,

bunchy, cresting, dead

Photo: APS Press

Blight, dieback

Photo: Dr. Ann Gould, NJAES

Aster yellows

Symptoms: stunting

chlorosis

phyllody

witches broom

Photo: Sabrina Tirpak, NJAES

Photo: Dr. Joe Peterson, Rutgers

• larvae leave distinct galleries


Pine Bark Beetle Wilt symptom = cause?Photo: APS Press

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Symptoms

• Caution

Not the be all – end all

Simple starting point

Don’t jump to conclusions

Need more information

Signs

Fruiting body, sporocarp,

cliestothecia, pycnidia,

mushroom, hyphae,

stroma, spores, conidia,

sclerotia, conidiophore,

perithecia, apothecia,

synnema, cyst, egg, cast

skin, nematode, insect,

plasmodium,

sporodochia, acervulus,

aecium, oospore,

zoospore, cirrhus,

basidiocarp, ascus,

sporangium, teliospore,

uredium

Photo: APS Press

Photo: Richard Buckley, NJAESPhoto: APS Press

Cedar Apple Rust

• telia on Eastern red cedar


Dogwood Anthracnose

The fungus moves into small stems and causes dieback

Photos: Dr. Ann Gould, NJAES

Discula destructa

Acervulus with conidia

Photos: Dr. Ann Gould, NJAES

Signs

• Caution

Not the be all – end all

Simple starting point

Don’t jump to conclusions

Need more information

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Pestalotiopsis spp.

Gray Leaf Blight

Photos: APS Press

Winter desiccation – March 2010

Photos: Richard Buckley, NJAES

Winter injury

Basic Diagnostics 101

1. Identify the plant

2. Observe the symptoms

3. Evaluate the predisposing conditions

4. Identify the sign

5. Synthesize the information

Step 1: Identify the plant

• Understand the needs of the plant

What are the horticultural requirements?

• Provides a list of pathogens

Key plant / key pest concept

Zoysia turns brown in winter in stark contrast to the perennial ryegrass


• Fungus - Volutella buxi

Volutella Stem Blight

• Host - Boxwood


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Proper identification is key

Understand the needs of the plant

What are the horticultural requirements?

Know your plant materials!


Step 2: Observe symptoms

• Define the problem

Examine the entire plant

Examine the plant community

Recognize patterns

Observe symptom progression

Recognize classic symptom expression




Photo: APS Press


Photo: University of California

Evaluate the entire plant


Lesser Peachtree Borer Botryosphaeria Canker

Photos: Debbie Miller, Davey Tree

Don’t be afraid to cut it up!

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Define the problem!

Identify dysfunctional plant part or plant system

What kind of symptoms do you see?

Photos: Richard Buckley, NJAESStep 2: Observe symptoms




Symptom Expression

Similar symptoms on

unrelated plants

are likely due to a

non-living (abiotic) cause

Similar symptoms on

related plants

are likely due to a living

(biotic) organism






Recognize patterns

Recognize Patterns

• Uniform - abiotic

• Random - biotic

Drop Spreader Disease

What can you say about this?


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Close shearing


Crown and Root Rot

Photo: APS Press

Drought stress


Bacterial Leaf Scorch






Recognize patterns



• Progressive – biotic

• Non-progressive - abiotic

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Crown and Root Rot

Photo: Richard Buckley, NJAES All plants rapidly decline after a week above 100oF


Heat stress





Recognize patterns


Recognize classic symptom expression

Typical symptoms of fungal pathogens

Fungi cause most plant diseases

Fungi attack all plant parts and cause all

possible symptoms

Central infection point

Rounded, even borders

Discolored margins

Dry rot

Signs frequently produced

• Fungus – Entomosporium mesculi

Entomosporium Leaf Spot

• Host – 60 species in the rosaceae



Crown and Root Rot


particular pathogens attack particular plant parts

Note: dry rot, discolored cambium, even border

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Maple Anthracnose

Photos: Sabrina Tirpak, NJAES

• Fungus – Aureobasidium apocrypta

• Host – sugar and red maplesNote: the gelatinous amber colored acervuli

Nectria Canker

Central Infection Point

Concentric circles

Rounded border

Discoloration of sapwood

Dry rot

SignsPhoto: Dr. Ann Gould, NJAES

Typical symptoms of bacterial pathogens

Bacteria attack all plants, but are most common on herbaceous hosts

Infection through natural opening or wound

Angular borders

Chlorotic halo

Water soaked rot

Tissue blight

Rotten smell

Bacterial Leaf Spot


Fire Blight

Bacteria ooze from natural openings on infected trees

Photo: APS Press

Fire Blight

Pollinators carry bacteria to nectar cells in flowers, which results in “spur blight”

Photo: APS Press

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Fire Blight

“Spur blight” progresses to branch blight

Photo: APS Press

Fire Blight

Severe disease


Photo: APS Press

Erwinia Soft Rot


Bacterial Blight of Cucurbit


Typical symptoms of viral pathogens

Virus attack many plants and cause

unusual symptoms

Abnormal growth

Abnormal color

Look for the vector

Latent / symptomless host

Rose Mosaic Virus

Photos: APS Press

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Rose Mosaic Virus

Photos: APS Press

Rose Mosaic Virus

Photos: APS Press

Impatiens Necrotic Spot





Photos: APS Press

Western flower thrips

adult

larva

Virus Vectors

Photos: APS Press


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Typical symptoms of physical injury

• Tip and edge scorch

– On individual plant parts

– On entire plant canopy

• Intervienal necrosis

• Loss of older needles

• Early fall color

• Premature defoliation

Loss of turgor first symptoms of drought

Drought stressPhoto: Ann Gould, NJAES

Tip and edge

scorch

Tip and edge scorch due to drought

Drought stressPhoto: University of California

Needles wilt and scorch too

Photos: Bruce Clarke, NJAES

Drought stress

Severe scorch after high heat stress


Heat stress

tip and edge scorch

over entire plant

top - down injuryPhoto: Richard Buckley, NJAES


Drought stress

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Damage is more severe on tough sites – July 11, 2010


Heat stress

Typical symptoms of chemical injury

• Symptom follows application pattern

– Patterns match application technique

– Cause and effect clearly evident

• Symptom expression relates to product:

– Toxic contact with exposed plant parts

– Uptake and translocation of toxic concentrations

Typical symptoms of chemical injury

• Necrosis of exposed plant parts

– due to direct contact with toxin

• Abnormal growth and color

– due to growth-regulator effects

– due to imbalances of nutrients

• Top-down, outside-in, tip-edge

– due to uptake of toxin

– on individual plant parts

– on entire plant canopy

Ozone toxicity

Photo: APS Press

Ozone causes tan, gray or metallic spots on upper leaf

surfaces during hot, sunny days in summer

Sulfur dioxide toxicityPhoto: APS Press

Sulfur dioxide is absorbed through the stomates in toxic concentrations;

damage was due to a poorly functioning heater and the plants recovered Burn from horticultural oil application on cloudy day

Oil phytotoxicityPhoto: Sabrina Tirpak, NJAES

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Injury to new growth due to Imprelis;

Do not apply under the drip-line!

Herbicide phytotoxicity


dicamba distorts flowers and causes upward

cupping of leaves; this sample injured by drift

Herbicide phytotoxicity


Salt phytotoxicity

De-icing salt damage – burn by contact

Photos: A&L Services

Sodium and chloride are absorbed and moved to the

leaf tips where they build to toxic concentrations

Photo: APS Press

Salt phytotoxicity

Boron toxicity

Photo: APS Press

Irrigation with high boron content water is also problematic

Phosphorous deficiency

Photo: APS Press

P deficiency rare in most NJ soils;

symptoms include purple discoloration

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Iron deficiency


High pH binds Fe in the soil and causes deficiency symptoms

Liquid fertilizer overdose

Typical symptoms of mechanical injury

• Breaks

• Bruises

• Punctures

• Cracks

• Chewing

• Girdling

• Root pruning

Lightning strike

Winter Injury

Heavy snow breaks branches and knocks stuff over


Winter Injury

Ice will do it too – January 1993

Photo: A&L Services


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Root damage

Damage to

the rootzone

= damage to

the canopy

Root damage

Photo: Ann Gould, NJAES

Do no construction under the drip line

String girdling

Photo: Ann Gould, NJAES

Stop sign

Step 3: Evaluate the predisposing conditions

• Analyze the site condition

• Record the weather condition

• Evaluate management program


• Analyze the site

Drainage

Shade and exposure

Air movement

Contour

Soil chemical properties

Soil physical properties

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Some wet sites are obvious

Note the white pine performs poorly on wet sites


Wet feet

Taxus does poorly on wet sites


Wet feet

Damage most severe on exposed surfaces (NE side)

Winter injury Pachysandra Stem Blight


Black Layer

Black layer – smells like a swamp, must be a swamp

Photo: Richard Buckley, NJAES Weed indicators of site conditions

High pH = plantain Low pH = sorrel

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• Record the weather condition

Temperature

Relative humidity

Rainfall

Evapotranspiration rates

Air quality

Time of year

Entomosporium Leaf Spot

severe disease on photinia



Nectria Canker


Rhizoctonia solani Predictive Model

• Warm nights

– Soil temperature >61oF

– Air temperature >59oF

• Extended leaf wetness

– 95% RH for >10 hours

– 0.1” rain or irrigation in

preceding 36 hours

Brown Patch


Leaf scorch and drop after high heat – July 11, 2010


Heat stress Frost damage

Cold temperatures

damage new

growth

Cause and effect

clearly evident

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Wet Feet and Wind

Note the lack of root biomass and the poor drainage



• Evaluate management program

Pruning

Fertility

Irrigation

Cultivation

Pesticide input

Wet roots turn black

Wet feet

Photo: Bruce Clarke, NJAES

Excessive mulch


Cupressaceae very hard hit by heat(Poor planting technique, crummy mulch, and excess irrigation didn’t help much)


Physical injury Herbicide phytotoxicity

Distorted growth = phenoxy herbicide

damage


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What fungicides, insecticides, and

herbicides were used on site?

How much and when?

Specific chemicals cause specific

problems – Can the materials used

cause the symptoms you see?


Chemical Injury

Step 4: Identify the sign

• Macroscopic observation

• Insect traps

• Microscopic observation

• Pathogen stimulation

• Pathogen isolation

• Antibody based test kits

• Special tests

Bagworm

• epidemicPhotos: Richard Buckley, NJAES

pseudosclerotia “Red threads” form on leaf tips

Red Thread


Macroscope

10 to- 60x

magnification

Juniper Tip Blight

Phomopsis spp.

pycnidia

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Oriental beetle, Exomala orientalis

Raster patterns indicate scarab species

Nematodes from turf soil

Compound

microscope

40 to- 400x

magnification

Copper Spot – Gloeocercospora sorgii

Note: sporodochia produce copious numbers of whip-like conidia


Bacterial streaming

Bacteria


Pink Snow Mold

Microdochium nivale

incubate plugs

to stimulate fungus


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Cyclamen Wilt

Bacteria laden “sterile” water is then streaked on media:

Which one is the pathogen?

Photo: Lane Tredway, NC State

Bacteriology 101

selective media

differential media makes target look different

Bacteriology 101

Photos: APS Press

only allows target to grow

Isolates are subjected

to a battery of

biochemical tests

Plant Pathology 101

Antibody-based test kits effective for Pythium


Detection

PCR ELISA

Plant Pathology 101

Photo: Dr. Ann Gould, NJAES Photo: Sabrina Tirpak, NJAES

Step 5: Synthesize the information

• Put it all together

Evaluate the symptoms

(host)

Consider the

predisposing factors

(environment)

Identify the sign

(causal agent)

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!!!! Caution !!!!

• Fungi don’t read the book

• Don’t jump to conclusions

• Keep an open mind

• Expect the unexpected

• Accumulate information

• Educate yourself

• Act on your hunches

Soil Testing and Plant

Diagnostic Services

www.njaes.rutgers.edu/services

What is “plant pathology”? · History of plant pathology •Theophrastus (c. 300 B.C.): Greek...

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Transcript of What is “plant pathology”? · History of plant pathology •Theophrastus (c. 300 B.C.): Greek...