3 2013 mg plant pathology - oregon state...
TRANSCRIPT
3/12/2013
1
Plant Pathology
Brian A. Charlton
OSU Research & Extension Agent
Objectives
Understand the concepts of disease, injury, and the signs and symptoms of plant pathogenic agents
Learn the basic biology of major disease agents of plants
Understand the interaction of pathogens, their host plants, and environmental factors on plant disease
Disease vs. Health in Plants
What constitutes disease in plants? Debate among scientists
Variability in ‘normal’ physiology difficult to define
A plant is considered healthy when: Able to carry out physiological functions to the
best of their genetic potential
If this does not occur because of interactions with pathogens or adverse environmental factors then disease may be present
3/12/2013
2
What is Disease?
Any malfunctioning of host cells and tissues that results from continuous irritation by a pathogenic agent or environmental factor and leads to development of symptoms.
Referred to as: Disease Agents
To determine the presence of a disease agent you need to look for: Signs and Symptoms
Disease vs. Injury
Is there a difference between disease and injury?
Yes . . .
Disease is a process that occurs over time.
Usually referred to as chronic
Injury is a more instantaneous form of damage.
Usually referred to as acute
Can be caused by insects, animals, physical damage, frost, chemical, etc.
3/12/2013
3
Signs vs. Symptoms
Signs are physical indications of the presence of a disease agent The pathogen itself or products and parts of the
disease agent
Symptoms are the internal or external effects of alterations exhibited by a plant suffering from disease
Common Symptoms
Abscission, blight
Blotch, canker
Chlorosis, defoliation
Desiccation, dieback
Dwarfing, enation
Epinasty, etiolation
Fasciation, flagging
Gall, mosaic
Mottle, necrosis
Rot, rugose
Russet, scab
Stippling
Water-soaked
Wilt
Witches’ Broom
Common Signs
Pest itself – e.g. aphid, nematode, spores
Bacterial Slime or gumosis
Conk, cyst
Frass, Fruiting body
Girdling, honeydew
Mole mounds, mycelia
Weather records, webbing
3/12/2013
4
Sign or Symptom?
Sign or Symptom?
Sign or Symptom?
3/12/2013
5
Sign or Symptom?
Sign or Symptom?
Sign or Symptom?
3/12/2013
6
Sign or Symptom?
Sign or Symptom?
Disease Triangle
3/12/2013
7
Disease Triangle (cont.)
Host relates to factors such as genetic susceptibility, plant age, growth rate, and plant stress.
Pathogen relates to factors such as virulence, amount of inoculum, pathogen density, fitness, etc.
Environment relates to physical parameters such as temperature, moisture, wind, light, etc.
Disease Triangle (cont.)
Disease results when the following occurs: Host is susceptible
Environment favors the pathogen
Pathogen is present, living, and active
Disease Agents
Separated into two major categories:
Non-infectious
Infectious
3/12/2013
8
Non-infectious Disease Agents
Can not be spread from one plant to another
Abiotic is another term used to describe non-infectious disease agents
Non-biological entities
Result of adverse interactions between the plant and its environment
Most Common Factors – Abiotic Disease
Nutrient Deficiencies and Toxicity
Water Stress
Temperature Stress
Chemical Injury
Mechanical - Cultural
Symptoms of Water Stress
Insufficient Moisture Wilting, Stunting
Leaf Scorch, Defoliation
Reduced fruit set
Excess Moisture Similar Symptoms + seed & root rot disease
Hypoxia: oxygen-starved roots Increased Respiration Rates
3/12/2013
9
Symptoms of Deficiency & Toxicity
Deficiency Necrosis
Chlorosis
Stunting
Rosettes at buds
Anthocyanin build-up
Toxicity Necrosis and Chlorosis most prevalent
Symptoms of Temperature Stress
Too Cold Frost or freeze damage – kills cells
Interferes with cellular processes
Inactivates crucial enzymes
Too Hot Necrotic – kills or ‘cooks’ cells
Cellular processes break down
Inactivates biochemical reactions
Types of Chemical Injury
Air pollution
Pesticides
Herbicides Plant growth regulators
Cell division inhibitors
Photosynthesis inhibitors
Cell membrane disrupters
Inhibitors of cell metabolism
3/12/2013
10
Types of Cultural Injury
Examples???
Infectious Disease Agents
Can be spread from one plant to another
Biotic is another term used to describe infectious disease agents
Biological entities
Known biotic pathogens: Fungi, bacteria, mollicutes
Nematodes, viruses, protozoa
Parasitic plants
3/12/2013
11
Common Symptoms of Disease
Leaf spots and blights
Ringspots
Mottling and mosaics
Root rot & Stem rot
Wilt
Galls & Cankers
Abnormal Growth – dwarfing, witch’s broom
Decay of flowering structures & seeds
Leaf spots and blights
Most common foliar symptoms
Leaf spots Necrotic lesions – delimited border
Does not continue to spread across leaf surface
Blights Severe withering
Rapid killing of leaves, flowers, shoots, fruit, entire plant
Cucurbit – Leaf Spot (Cercospora)
3/12/2013
12
Rose – Black Spot (Diplocarpon)
Late blight lesions
Early blight lesion Gray mold lesion
Sporulation on underside of potato leaf
fluffy white sporulation on lesion’s edge
3/12/2013
13
Rose - Botrytis blight
Leaflet collapsing from late blight infection
Ringspots
Chlorotic rings on leaf surface
Contain green tissue within the ring
Associated with some viral diseases
3/12/2013
14
Rhododendron Necrotic Ringspot
Mottling and Mosaics
Disruptions in plant tissue pigments
Mottling Irregular pattern of indistinct light & dark pigment
Mosaics Intermingled patches of normal and light green or
yellowish color
Most often associated with viral disease
Potato Virus Y
3/12/2013
15
Root Rot & Stem Rot
Root Rot Decay of living root tissue (root hairs, cortex, etc)
Discolored, softened, or disintegrated tissue
Fungi and Bacteria most common causal agents
Stem Rot Essentially the same as root rot
Tissues affected are cambium, pith, and structural tissues
Bean – Root Rot (Fusarium)
Corn –Crown Rot (Fusarium)
3/12/2013
16
Wilt
Loss of rigidity or drooping plant parts
Insufficient water in plant
Diseases can impact the following: Water transport tissues – xylem
Water retention in plants
Tomato – Fusarium Wilt
Tomato – Fusarium Wilt
3/12/2013
17
Cucurbit – Bacterial Wilt (Erwinia)
Galls
Abnormal swellings or overgrowths (tumors)
Can occur on roots, stems, leaves, etc.
Composed of unorganized tissue resulting from stimulus provided by infective organism
Forsythia -- Stem Gall (Phomopsis)
3/12/2013
18
Rose – Crown Gall (Agrobacterium)
Cankers
Localized sunken necrotic lesions on stems, branches or twigs.
Surrounded by living tissues and grow concentrically
Colonize new tissue at their margins
Apple – Perennial Canker (Cryptosporiopsis)
3/12/2013
19
Fir, Douglas – Stem Canker (several fungi)
Abnormal Growth
Stunting
Dwarfing
Epinasty
Witch’s Broom
3/12/2013
20
Decay of Flowering Structures & Seeds
Bunts
Smuts
Scabs
Ergots
Blasts
Seed Rot
Smuts and Ergot
Scab
3/12/2013
21
Bean – Seed Rot (Rhizoctonia, Pythium, etc.)
Brief Symptom Schematic
Symptoms Bacteria Fungi Viruses Nematodes PhytoplasmaWilts X X X XLeaf Spots & Blights X X XFruit Rots X XRoot Rots X X XDamping Off XDistorted Growth X X X X X
Fungi
Non-photosynthesizing eukaryote
Produces enzymes to absorb food
Responsible for 85% of all plant disease
Live on organic matter
Reproduce primarily by spores
Perennial inhabitants of all ecosystems
3/12/2013
22
Fungi Terminology
Hypha – tubular thread of connected single cells (hyphae = plural)
Mycelium – hyphal threads collectively growing together
Thallus – interwoven mass of mycelia
Stroma – dense organized thallus tissue
Sclerotia – dense masses of stroma tissue Overwintering structure
Fungi Terminology (cont.)
Spores – sexual reproductive structure Essentially like seeds
Fruiting Body – structure that produces spores
How do Fungi Enter Plants
Through Natural Openings between Plant Cells (stomates)
Penetrate directly into the plant cell by digesting the cell wall
Wounds are an ideal port of entry
3/12/2013
23
Role of Moisture in Fungal Disease
Favors Growth
Favors Spore Production
Favors Spore Germination
Favors the Spread of Spores
3/12/2013
24
Where Might Control Tactics be Useful?
Bacteria
Single-celled microscopic organism
Multiples by cell division
Composed of individual cells
Nearly 200 species cause disease in plants
Identified by physiology
Perennial inhabitants of all ecosystems
Bacteria Terminology
Flagella – tails that aid in mobility (water)
Gram stain – method of identification Gram Positive and Gram Negative
Based on staining process
Most plant pathogens are G Negative
Can be vectored by insect activity
Composed of a cell wall and membrane
3/12/2013
25
How do Bacteria Enter Plants?
Need a wound or natural plant opening Leaf stomata or certain flower parts
Spread of Bacteria Occurs via Water (rain, irrigation, plant liquids)
Plant propagation (cuttings)
Dirty tools (pruning)
Main Genera of Plant Pathogenic Bacteria
Agrobacterium - tumors
Clavibacter – ringrot, wilt, canker
Erwinia – fireblight, softrot
Pseudomonas – leaf spots, wilts
Streptomycetes - scab
Xanthomonas – black rot
Xyella – obstructs xylem vessels (vectored)
3/12/2013
26
Viruses
Small particle consisting of genetic material (DNA, RNA, etc) encased in a protein capsule
Can only reproduce within living organism
Become systemic in their host plants
Are some of smallest known pathogens
Pesticides not effective against specific virus
Viruses (cont.)
Use a plant’s cellular machinery and chemical processes to replicate
Particle accumulation in plant cells alters cell physiology and obstructs cellular processes
Three main morphologies Rod-shaped
Sphere-shaped
Cylindrical rod-shaped
How do Viruses Enter Plants?
Via Insects (aphids, leafhoppers) Sucking mouth parts
Mechanical Spread Sap transmitted
Machinery, rough handling
Propagating Materials Vegetative organs (tubers, bulbs)
Occasionally seed-borne
3/12/2013
27
Management of Viral Diseases
Avoid wounding plants – avoid mechanical
Border Plants, Trap Crops, Buffer Strips
Rogue Infected Plants
Resistant Varieties
Use clean propagating material
Control Vectors Themselves
Alternate Habitats
Nematodes
Microscopic, worm-like animals
Live saprophytically in water and soil
Live as parasites on plants
Are True Animals
Reproduce Sexually
Parthenogenetically – NO MALES! Essentially clones
3/12/2013
28
Nematodes (cont.)
Life Cycle – egg, juvenile, molting, adult
Eggs – can remain dormant for long periods Suitable host - root exudates trigger hatch
Juvenile – look similar to adults but smaller 4 stages – determine sex
Feeding causes damage
Adults
Four Categories of Nematodes
Migratory Ectoparasites Never enter plant tissue, feeding and moving
Migratory Endoparasites Enter plant tissue and move from cell to cell
Sedentary Ectoparasites Remain outside plant tissue w/ long-term feed site
Sedentary Endoparasites Permanent feeding site inside plant tissue
Are all Nematodes Bad?
Most are Beneficial
Several are Plant Pathogenic
Some Vector Viruses Stubby-root
Yield Reducing at High Populations
Serve as Infection Courts for other Disease
Quality Issues with Viruses CRS
3/12/2013
29
Corky Ringspot
Are Nematodes Found Above Ground?
Some infect above ground portions of plants Stem nematodes in Alfalfa Leaf deformations Loss of photosynthetic surface area
Most are found below ground Root and Rhizome Infections Bulb and Tuber Infections
Mostly reside in top foot of soil Migratory Ectoparasites – depths of 5 ft.
3/12/2013
30
Management of Nematodes
Exclusion – avoid introduction
Resistant Varieties
Crop Rotation Non-host
Green Manure
Soil Fumigants - Nematicides
3/12/2013
31
Plant Parasitic Plants
Derive Nutrition and in some cases Physical support from host plants
Haustoria – similar to a root
Haustoria – penetrates host plant Absorb water
Absorb Nutrients
Absorb Light
Symptoms of Plant Parasitism
Wilting
Stunting
Chlorosis
Deformation of Plant Tissue
Examples Dodder
Witchweed – Broomrapes
Mistletoes
Dodder
Lacks chlorophyll
Relies on host for organic nutrients, minerals, and water
Most common in alfalfa, potatoes, onions, beets Common pest in Treasure Valley
3/12/2013
32
Cucurbit – Dodder
Mistletoes
Parasitize woody perennials
Have chloroplasts but rely on host for water and mineral nutrition
Can cause substantial loss to tree industries
Common on Oak Trees – Hwy 140 to Medford
Oak – Mistletoe
3/12/2013
33
Witchweed and Broomrape
Witchweed Root parasitizer
Does produce some chlorophyll
Limited to SE USA
Broomrapes Mostly lack chlorphyll
Of little economic importance to temperate regions
Management of Parasitic Plants
Exclusion
Prevent Spread
Crop Rotation – non-hosts
Biological Control
Resistant Varieties
Chemicals
3/12/2013
34
Disease Cycles
Pathogen Survival
Inoculum Production
Pathogen Dispersal
Deposition
Germination
Host Penetration
Intrahost Spread
Secondary Inoculum
Pathogen Survival
Overwinter from one growing season to another via five protective environs:
Crop Residue Provide nutrients
Physical buffer from the elements
Seed Transported by man or animals
Pathogen may be on surface or inside seed
Pathogen Survival (cont.)
Soil Dormant structure - sclerotia
Host Plants Perennial Plants – dormant or semi-dormant state
Insects Dormancy
Vectoring – Persistent & Non-persistent manner
3/12/2013
35
Inoculum Production
Inoculum – Established pathogens can produce material that incites new infections Fungal sporulation
Bacterial cell division
Nematode - eggs
Pathogen Dispersal
Wind
Water
Insects
Soil Movement
Propagative Plant Materials
Human Interactions
Deposition
Once pathogens are dispersed into the environment they must be able to come into contact with their new host
Often referred to as juxtaposition
3/12/2013
36
Germination
Favorable Environmental Conditions Optimal Moisture
Optimal Temperature
Host Penetration
Suitable Infection Court Natural plant openings
Stomates, lenticels, inflorescences, wounds
Direct Penetration
Intrahost Spread & 2o Inoculum
Intrahost Spread Movement within plant
Local
Systemic
Secondary Inoculum Survival Strategy to reproduce
Polycyclic – production of secondary inoculum
Monocyclic – one sporulation event per season
3/12/2013
37
Disease Triangle
Disease Triangle (cont.)
Host relates to factors such as genetic susceptibility, plant age, growth rate, and plant stress.
Pathogen relates to factors such as virulence, amount of inoculum, pathogen density, fitness, etc.
Environment relates to physical parameters such as temperature, moisture, wind, light, etc.
Disease Triangle (cont.)
Disease results when the following occurs: Host is susceptible
Environment favors the pathogen
Pathogen is present, living, and active
3/12/2013
38
Control of Infectious Plant Diseases
Exclusion
Avoidance
Eradication
Protection
Resistance
Tolerance for Disease Seed Certification
Disease Diagnosis
Define the Real Problem
Look for Patterns – uniform vs non-uniform
Determine Time Development of Damage
Look for Signs and/or Symptoms Root, storage organs (tubers, bulbs)
Seedling Disease, Leaf, Stem, Branch, Trunk
Flower, Fruit
Determine Cause of Plant Disease
Disease Diagnosis (cont.)
ASK QUESTIONS Varieties
Cultural Practices
Irrigation Practices
Seed Source
Patterns, Affected Plant Parts
When did Symptoms/Signs Develop
Take Representative Samples
3/12/2013
39
3/12/2013
40
3/12/2013
41
ASK MORE QUESTIONS
Consult All Resources Possible Publications
Reference Books
OSU Research & Extension Centers
Private Consultants
Web-based References – BE CAREFUL
Experience Best Teacher
References
OSU Plant Disease Clinic
Iowa State University – MS Agronomy Agron 514 and 533
Cornell Cooperative Extension
Additional Slides by Dr. Cindy Ocamb
Cornell Cooperative Extension
ISU Agronomy
Plant Pathology – Cram Session!! Any Questions?
Brian A. Charlton
OSU Research & Extension Agent