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

by OneClass171827 , Fall 2013
12 Pages
Fall 2013

Course Code
Biology 4218A
Graeme Taylor
Study Guide

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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 Epidemiology Control - causes - disease - principles - biology - spread - methods - taxonomy - disease cycle - forecasting00 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  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 Chemicals : factors: - air pollutants (e.g. - temp. ozone, sulfur dioxide, - moisture nitrogen oxides)** - light - herbicides - nutrients - deicing salt - pH - often no spread is observed Symptoms: - regular distribution or uniform damage - arranged irregularily - clear lines demarcating healthy vs. damaged - the transition from injured to healthy is more - more than one plant species may be affected diffuse - linear strips - varying sizes and stages of severity - more common near edges of host population **e.g. Common Air Pollutants and Symptoms - ABIOTIC Air polluatant Source Symptom ozone - internal combustion engine - flecking (upper leaf) exhaust + sunlight - stippling - mottling - tipburn (conifers) - stunting PAN (peroxyacetyl nitrates) - bleaching - bronzing (lower sides of leaves) Sulfur dioxide - Industrial processes - Interveinal necrosis - coal burning (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 - defoliation - Industrial processes - senescence - Leaf deformation - fruit drop Dog Spot Dog urine – release of dessicates turf grass leaves, nitrogen from the urine can causing a roughly circular spot stimulate grass growth of dead leaf blades around the edge of the dead  same symptoms associated spot with fertilizer spills OTHER Wintering, salt, lack of calcium, frost, lightning, sunburn, edema (accumulation of water), excess boron, SO2, herbicide Observing patterns: - 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 - occur distant to site of infection e.g. root rots, leaf spots, blights, galls,e.g. above ground symptoms of root cankers 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 - dampening off - stem rusts - leaf spots - sclerotinia (white mold - chlorosis fungus) - powdery mildews Virus - none - mosaic pattern - yellow leaves - plant stunting Bacterial - ooze - leaf spots - water soaked lesions - fruits spots - bacterial streaming - cankers - galls Lecture 3: History and Significance of Plant Pathology - Early thoughts of Plant Disease - Homer writes of therapeutic properties of sulfur on plant disease - Democritus recommended controlling plant blights by sprinkiling plants with the olie grounds left after extraction of the olive oil V. little info on controlling plant disease was written till about 1200A.D – e.g. mistletoe found as a parasitic host on another plant. – removal of mistletoe by pruning = cured host plant - e.g. 1670 – Thoulier observed “Holy Fire” – deadly disease of humans in north Europe – was not seen bc of contamination but bc of ergot contaminated grains - Hooke invents microscope – discoveres units called cells -1674 Leewenhock improves the lens on microscope and examines anatomy of plants, fungi, protozoa, sperm, blood and bacteria - 1735 – Carl von Linne – publishes Systema Naturae – established diagnosis of plant species and binomial nomenclature of plants - 1739 – Antonio Micheli describes new genera of fungi and reproductive structures, note shtat they arise from spores vs. “spontaneous generation theory of time” – nobody believs him  - 1743 – Needham observes nematodes in kernals – fails to see where they are from - 1755 – Tillet – discovers smut and its ability to be stopped with copper sulfate (concludes it is a posionous substance vs. plant disease) - 1807 – Prevost – repeats inoculums with copper sulfate – concludes correctly that smut spores are what cause the plant disease, and the sulfate treatment inhibits germination of spores - 1858 Charles Darwin – published The Origin of Species by Mean of Natural Selection - people still think that spores are the result rather than the cause of disease - dramatisized in 1840’s with potato blight – till deBary proves otherwise – cause is from disease, he also worked with many smut and rust fungi and those that cuase downy mildews (e.g. Sclerotnia – rotting of vegetables) - 1860’s Lousi Pasteur prove that microorganisms were produced from pre-existing microorganisms and that most infectious diseases were caused by germs  latter established in “the germ theory of disease” paper (moving past old spontatneous generation theory - 1864 – Pasteur invents pasteurization - 1870’s Kuhn – works controls for infection of smut particularily seed treatments  states that unfavorable environments can be caused by parasitic organism such as insects fungi and parasitic plants - showed that plants need alternate hosts to completely finish their life cycles - Robert Petri – developed artificial nutrient media for culturing the microorganisms - + Robert Koch who establishes necessary steps to prove that a microorganism is the caused by an infectious disease, in which certain conditions must be met - 1887 – produces Koch’s postulates Nematodes - 1743 Needham sees them - De
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