Clemson Extension

Putting Knowledge to workWalker Miller Prof. Emeritus

Agrisystems productivity& ProfitabilityEconomic and community developmentEnvironmental ConservationFood safety & NutritionYouth Development& families

The Happy Berry Inc and Happy Berry Consulting

Walker Miller, Plant Pathologists Professor Emeritus Clemson

University, Certified Crop Advisor #18472, SC Licensed Pesticide

Applicator #1063, Owner & operator of The Happy Berry Inc

•Other Sponsors

Our objective todayMake a practioner out of you…Clemson has a Plant Problem ClinicAs a Master Gardener you will have contact w/clients that have plant problemsYou are the eyes and ears of the clinicYou are a vital link in communicationWith experience you will make your own diagnosis

Our objective

To help you integrate what you have learned or will learn about soils, insects, horticulture into a process that will enable you to become a Master Gardener to help others solve their

plant problems

Vocabulary is the key to communication

Plant Pathology

The Study of Plant Disease

[pathos – suffering]

[ology – study of]

DiseaseAny deviation from normal growth,

structure or function of a plant that is a continuous condition which

produces visible symptoms, thus affecting the economic quality or

value of that plant.

The three must have items for disease to occur

Plant Disease triangle

Susceptible host

Causal agentFavorable environment

Favorable Environment

Susceptible Host

HostA plant species that

provides some or all of the nutrients for a particular

plant species

Virulent Pathogen

Pathogen

Any agent of causing a plant disease

ParasiteAny organism that reside in or on another

organism and derives some or all of its nutrients from the host organism. Parasites

can be either obligate [surviving only in or on a living organism] or facultative [surviving on

live or dead organisms].

All pathogens are parasites but not all parasites are pathogens

Saprophyte

An organism that derives all of its nutrients from dead

organic matter as contrasted to a parasite that lives in or

on living tissue

Facultative Saprophyte – Is a parasite that has the faculty to

live as a saprophyte

Facultative Parasite - Is a saprophyte that has faculty

to live as a parasite

Fungal pathogens range obligate saprophyte to obligate parasite

Koch’s PostulatesProof of Pathogenicity

• The pathogen must be constantly associated with the disease

• The pathogen must be isolated and grown in pure culture and characterized

Koch’s PostulatesProof of Pathogenicity

• The isolated pathogen must cause the identical disease in inoculated plants of the same variety

• The pathogen must be isolated from inoculated plants and be identical to the original isolate

Infectious Disease

A disease that can be spread from one plant to another since it is caused by living

organism

Agents of Disease

Noninfectious plant disease

A disease incapable of being spread from plant to plant since it is caused by non-living environmental factors

More common than infectious

Genetic diseases

Injury

Damage to a plant by some factor [insect, (?) wind, hail, machinery]

that occurs over a short period of time rather developing in a continuous

sense as with disease.

Non Infectious Disease Agents

• Nutrient imbalance

• Temperature [incident vs. imbalance]

• Water imbalance

• Light imbalance

Symptoms

Visible or measurable expression of disease by a plant

SymptomsVisible or measurable expression of disease by a

plant

Leaf blight – sudden deaf of tissue

Leaf spot – localized death of tissue

Fruit rot - disintegration

Wilt – interference with water movement

Galls – cancerous growths

Cankers – depressed elliptical areas

Root rot – disintegration

SymptomsVisible or measurable expression of disease by a plant can be classified

• Necrosis – rots, spots, blights

• Reduction photosynthesis• Yield

• Yellowing vs. chlorosis

• Disruption of translocation

• Localized – spots, blights, galls, cankers

• Systemic – dieback, decline, stunting, wilt

FunctionVs.Symptom

SymptomsVisible or measurable expression of disease

by a plant can be classified

The point is interpretation- symptoms give you clues as to what agent of disease might be, where to look forwhat the problem is, what samples to collect…

Signs

The obvious presence of a pathogen in the form of spores, mycelia,

sclerotia, bacterial ooze, fruiting structure etc.

Is there any sign (s) of the pathogen (s) present on the plant ?

Pathogen signs

• Mycelia

• Ooze

• Fruiting bodies

• Rusts

• Sclerotia

• Mushrooms

• Conidiophores and spores

Spore

The fungal structure analogous to a seed in higher plants. It serves to reproduce and spread the fungus.

Sexual or asexualVariable in shape and sizeVariable in color and number of cells and variable in presentation

Reason for sex and hazard of cloning

Lets take a break !!

Infectious Disease Agents

• Fungi• Bacteria• Mollicutes – spiroplasmas & phytoplasmas• Viruses and viroids• Pirons – infective replicating proteins• Nematodes• Protozoan• Seed plants• Insects???

Stages in disease development

• Inoculation

• Penetration

• Infection

• Incubation

• Reproduction

• Dissemination

• Survival of adverse conditions

Diagnosing fungal diseases

• Symptoms

• Signs, morphology

• Culturing facultative pathogens

• Elisa immunoglobulin reactions

• PCR

Bacterial disease development

• Inoculation

• Passive entrance/ resident

• Multiply to threshold number

• Dissemination

• Survival

Bacterial diagnosis

• Symptoms

• Morphology and staining

• Growth on substrates or lack of

• Enzyme activity or lack of

• Hypersensitive reactions

• ELISA/immunoglobulin assays

• Fatty acid profiles

• PCR probes

Viral disease development

• Inoculation

• Take over of cell DNA/RNA metabolism

• Replication

• Spread within plant

• Vector relationship

Viral diagnosis

• Symptoms

• Inclusion bodies and electron microscopy

• Host range studies

• Non host reactions / hypersensitivity

• Elisa/immunoglobulin

• PCR

Diagnostic procedures can be very expensive

Principles of Disease Management

• Exclusion• Quarantine, certified propagules, protective coverings and

environmental manipulation

• Eradication• Crop rotation, surgery, sanitation

• Protection• Plant pharmaceuticals, Direct…cides bio & non bio, Indirect SAR, vector

control

• Resistance• Non host, true resistance and apparent resistance

Environmental manipulation

• Arid area seed production

• Proper time &depth of planting

• Avoidance of wet soils – raised beds

• Proper plant spacing, orientation &air drainage

• Manipulating green house vents

Sometimes given a special category of cultural control

SusceptibilityThe host fails to recognize an

invading pathogen ---therefore does not activate any resistance structural

or biochemical defenses

True resistancePathogen and host evolve together

Gene for gene relationship

Mono, oligo, polygenic

SAR

“Plantibodies”

Genetically Modified Plants

• Normal gene flow in the environment

• Transgenics• Within species - Marker assisted breeding

• Across species - ditto

• Across genera and families

• Across kingdoms

The Plant Problem Clinic

•Service

•Education

•Research

Service• Diagnosis – takes dollars and time

• Control recommendations

• Electronic technology to to speed response• Agents trained to send specimens via the web

• Shared with specialist across the state and around the country/world where needed

• Prompt reply once diagnosis is confirmed

Form a diagnostic hypothesis

What evidence is needed to confirm that hypothesis?

Confirm or deny the hypothesis

If hypothesis can not be confirmed or denied ---present as hypothesis

not fact

The cost consideration

Balance the cost of diagnosis with risk exposure and or willingness to

pay

Education

• County agent training

• Master gardener training

• Student education

• Support Home Garden Center

• Landscape industry training

• Annual and other reports

Research

• Detect new diseases • A vital link in homeland security• Cooperate regionally, nationally and

internationally• Maintain database of pathogens

• Evaluate new techniques• Support disease management research• Apply research to the regulatory process

Thank you for this opportunity!

Questions Discussion

Please visit us at The Happy Berry in Six Mile

Or on the web at

www.thehappyberry.com