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Midterm

Biology 4218A Study Guide - Midterm Guide: Verticillium, Lightning, Ethylene

12 pages106 viewsFall 2013

Department
Biology
Course Code
Biology 4218A
Professor
Graeme Taylor
Study Guide
Midterm

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4218 – Microorganisms and Plant Disease:
Lecture 1 – Introduction (Dr. Gardiner)
Pytopathology  phyto = plant, pathos = suffering/disease, logos = the study of
Plant Pathology
Etiology
- causes
- biology
- taxonomy
Epidemiology
- disease
- spread
- disease cycle
- forecasting00
Control
- principles
- methods
Why study plant pathology??
- productivity $$, world food shortages, ecology
Lecture 2 – Diagnosis and Symptoms (Gardiner):
Disease symptoms:
- symptoms are the plant’s response to disease
- symptoms reflect the physiological function of the plant that is disrupted or impaired
- disease can be categorized according to their symptoms
e.g. root rots, fruit spots, vascular wilts, abnormal growth, leaf spots
Disease Diagnosis
Homework assignment aps.net.org  Plant disease Diagnosis; review to this lecture
Disease Diagnosis Order:
1. Know what is normal
2. Know what is possible:
- seek out literature that categorizes disease by host
- aps compendia on disease of specific hosts
- APS database
- USDA publications
- PNW online guide to plant disease control
3. Collect Background Info:
- identity of host  cultivar (plant produced in cultivation via selective breeding)
- planting date and environmental conditions at planting
- seed source, seed treatment, seed germination
- Disease history: description of first sumptoms, when first noted, spread, specific factors
associated with disease appearance.
- Cultural practices, chemicals, and dates of application
- field and crop history
- weather conditions during season and period of disease development
4. Check Symptoms
5. Observe Patterns and 6. Ask Q’s
Abiotic? Or Biotic?
Abiotic Biotic
Environmental
factors:
Chemicals :
- air pollutants (e.g.
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- temp.
- moisture
- light
- nutrients
- pH
ozone, sulfur dioxide,
nitrogen oxides)**
- herbicides
- deicing salt
- often no spread is observed
- regular distribution or uniform damage
- clear lines demarcating healthy vs. damaged
- more than one plant species may be affected
- linear strips
- more common near edges of host population
Symptoms:
- arranged irregularily
- the transition from injured to healthy is more
diffuse
- varying sizes and stages of severity
**e.g. Common Air Pollutants and Symptoms - ABIOTIC
Air polluatant Source Symptom
ozone - internal combustion engine
exhaust + sunlight
- flecking (upper leaf)
- stippling
- mottling
- tipburn (conifers)
- stunting
PAN (peroxyacetyl nitrates) - bleaching
- bronzing (lower sides of
leaves)
Sulfur dioxide - Industrial processes
- coal burning
- Interveinal necrosis
(broadleaf)
- Tip necrosis (conifers)
Nitrogen oxides - bronze necrosis
Acid Precipitation Sulfur + Nitrogen oxides - chlorosis and necrosis of
leaves
- stunting
Hydrogen fluoride - industrial processes - marginal and tip necrosis
Ethylene - Internal combustion engine
- Industrial processes
- defoliation
- senescence
- Leaf deformation
- fruit drop
Dog Spot Dog urine – release of
nitrogen from the urine can
stimulate grass growth
around the edge of the dead
spot
dessicates turf grass leaves,
causing a roughly circular spot
of dead leaf blades
 same symptoms associated
with fertilizer spills
OTHER Wintering, salt, lack of
calcium, frost, lightning,
sunburn, edema
(accumulation of water),
excess boron, SO2,
herbicide
Observing patterns:
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- seedborne incoulum vs. inoculums sources from far away
- aggregated or contagious distribution
- very common pattern? - indicates random distribution followed by spread of disease within
host population
- vs. patch distribution; characteristic of root infecting pathogens, often delimitated by the
topography/ soil type
Observing Patterns: Within a Plant – Plant patterns
Primary vs. Secondary Symptoms
- @ site of infection
e.g. root rots, leaf spots, blights, galls,
cankers
- occur distant to site of infection
e.g. above ground symptoms of root
rot, crown rot, or vascular wilt,
nematode damage
e.g. Root rot Lesions on roots - Foliar chlorosis
- stunting
- root and top dieback
e.g. wilts Vascular discoloration Wilt of leaves, defoliation
e.g. Leaf spot Necrotic lesion Chlorosis, defoliation
Stem Cankers Sunken lesion Distal branch dieback
Other examples: Abiotic = scorch, application problems due to improper application of
fertilizer
Vs. Biotic = gray mold
7. Lab Consultation and Testing
- identify the pathogen
- microscopic observations
- incubate disease tissue in moist chamber
- culture diseased tissued in Petri dishes
- biochemical tests: serology (serum/ fluid analysis), DNA
- chemical tests for abiotic causes, nutrient deficiency
- Koch’s postulates
8. Final Diagnosis
- Diagnosis is a form of hypothesis testing
- Diagnosis is detective work
- Multiple pieces of evidence may be required
- Evidence must be weighed accordingly
Diseases Signs: Symptoms
Fungal - leaf rusts
- stem rusts
- sclerotinia (white mold
fungus)
- powdery mildews
- dampening off
- leaf spots
- chlorosis
Virus - none - mosaic pattern
- yellow leaves
- plant stunting
Bacterial - ooze - leaf spots
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