Pathogen Information and Management

K.A. CochranAssistant Professor & Extension SpecialistTexas A&M University AgriLife Extension Dept. Plant Pathology & Microbiology

A disruption of a plant that interferes with normal structure, function, or growth caused by a pathogen (or other factors) leading to development of symptoms.

What is plant disease?

Baudoin, 2007

Basic disease cycleOverwinter: (plant or vector), 

debris, soil

Plant host & Favorable conditions available

Infection‐Pathogen gains 

entry & overcomes 

plant defenses

Pathogen causes disease symptoms in 

plant

Pathogen reproduces & 

spreads Some pathogens have a secondary cycle within a single season

Disease Symptoms & Signs

Symptoms-changes in plant growth or appearance in response to a pathogen◉ Yellowing◉ Wilting◉ Necrosis ◉ Stunting◉ Galls, witches’ brooming

Sign- direct evidence of the pathogen, such as actual pathogen tissue◉ Fungal tissue, sporulation◉ Bacterial ooze

What are Symptoms vs. Signs?

Sign vs. Symptom

Symptom: Chlorosis, necrosis, wiltingSign: Acervuli (sporulation of fungi)

Plant Pathogens & Disease Examples

Single celled organisms◉ Prokaryotes

Everywhere in environment◉ Only some are pathogenic to

plants

Some pathogenic to humans can survive on plants◉ E. Coli, Listeria sp., others

Most that cause disease in plants won’t make humans sick

Bacteriahttp://erec.ifas.ufl.edu

UMN Ext. LSU PLPA Blog

MN Dept Ag

ohioline.osu.edu

Sub-microscopic Many are spread by vectors (insects) Some by mechanical means, seed Yellowing, loss of vigor, death of plant in some cases Best control is vector control, clean practices

Viruses

Peanut leaf ‐TSWV

pnwhandbooks.org

www.agritotal.com

www.apsnet.org

Microscopic “worms” Infect plants and feed on

nutrients Most are root feeders Sandy or clay soil, different

species

Nematodes

http://cdn.phys.org

www.soilquality.org.auwww.wageningenur.nl http://utahpests.usu.edu

Basidiomycetes◉ Mushrooms◉ Conks◉ Puffballs◉ Fairy rings

Fungi

Wikipedia.org

ag.umass.edu

Ascomycete-cup fungi◉ “Imperfect” too◉ Most plant pathogens, but

many important ecosystem members

Fungi

c1.staticflickr.com

www4.uwsp.edu

Recognize fungi and better understand how it lives & spreads

Fungal Structures

Mycelium, hyphae: Vegetative growth, threadlike structures. 

Somatic tissue‐the “body” of fungus. 

webstercountyschools.org

Fungal Reproductive Structures

commons.wikimedia.org

Acervuli of Colletotrichum

Phomopsispycnidia

www.discoverlife.org

Phomopsispycnidia in stem

www.missouribotanicalgarden.org

Ascospores Basidiospores

Fungal Spores & Structureswww.cals.ncsu.edu

Perithecia with asci

Wikipedia.org

lifeandscience.org

Fungal Spores & Structures- Conidia (clones!)

Cliffnotes.com

usyd.edu.au

thegordonlab.net

Conidia are asexual  spores, and come in large variety of shapes & sizes

Sclerotia- tough fungal tissue propagules in plant material/soil lasting years◉ Rhizoctonia solani, others

Other reproductive and survival structures

Oomycete-water molds◉ Downy Mildew◉ Root rots

◉ Pythium, Phytopthora

Fungus-like microbes

livegpath.cals.cornell.edu

Rutgers.edu

Oomycete Vs. “true” fungi dispersal

Apsnet.org

webstercountyschools.org

This Photo by Unknown Author is licensed under CC BY‐NC‐ND

Active & passive Passive

Disease Management

Basic disease cycle, the triangle, and management

Overwinter: (plant or vector), 

debris, soil

Plant host & Favorable conditions available

Infection‐Pathogen 

gains entry & overcomes 

plant defenses

Pathogen causes disease 

symptoms in plant

Pathogen reproduces & 

spreads

Opportunities for management at every phase!

Host

PathogenEnvironment

Resistant or immune plants

Avoidance via cultivation techniques

Exclusion

Protection

Eradication

Therapy

Management Strategies

Prevention

Treatment

Employing genetics and traits of the plant to naturally resist pathogens

Resistance & Immunity

Direct ◉ Tolerance vs. Resistance

◉ Tolerance=plant can do well in spite of pathogen colonizing some tissues

◉ Resistance= plant prevents disease from occurring on genetic level

Indirect◉ Plant traits such as waxy

cuticle can prevent pathogens from gaining entry

Avoid disease development by making environment unfavorable for the pathogen with cultivation techniques

◉ Adjusting irrigation method and timing, use of mulch, tillage◉ Different planting sites ◉ Different planting times ◉ Using adapted varieties

Avoidance

Slide by K. Ong

Slide by K. Ong

Slide by K. Ong

Slide by K. Ong

What is Integrated Pest Management?

Using multiple disease control approaches to prevent and manage 

plant diseases

Focus on prevention by creating an unfavorable

scenario for disease development

Effective, evidence based

Ecologically responsible

Multi‐faceted

Focus on Prevention 

Try to prevent disease- Maintain cultural practices (watering, pruning, etc) that make the environment unfavorable for disease and promotes healthy vigorous plant growth. ◉ Know your host Know what it needs, Stressed plants=disease more likely◉ Drip irrigation to reduce leaf wetness period, prevent & reduce disease

Sanitation: physically remove inoculum sources, tillage◉ Debris, alternate hosts◉ Clean all tools, shoes well.

◉ Bleach (1:10) soak tools in tub, dry

Use least toxic chemical option if needed

Use resistant/ immune selections to prevent disease again

Example of Implementing IPM