Plant Pathology Test 3
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- What are the "Big Three" when dealing with forest pathology?
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Fusiform Rust
Pitch Canker
Annosum Root Disease - What aspect of the disease triangle most influences forest diseases and give examples?
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Environment
- example: vascular wilts and Xylella fastidiosa; in warmer areas - What is bacterial leaf scorch?
- bacterial disease caused by Xylella fastidiosa that affects sycamores, oaks and other species
- What is Chrysoporthe cubensis?
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- on live oak
- a fungus related to the Chestnut Blight fungus
- canker fungus found in tropical areas
- had not been previously reported on Quercus (now recovered 3 times) - What is annosum root disease?
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- occurs on pine
- colonizes freshly cut stumps
- affects sandy, drained sites
- borax can be used to prevent infection - What are the symptoms of armillaria root rot?
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- mushroom root rot
- causes mycellial felts or mats
- clustered/gilled mushrooms
- rhizomorphs - What are the symptoms of phytophthora basal canker?
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- occurs on laurel oak
- bleeding stem cankers with callus folds
- water-soaked lesions in the inner bark with black "zone lines"
- Nectria perithecia associated
- similar appearance to SOD - What is affecting the mortality of redbay?
- a bark beetle (Xyleborus glabratus) and a blue stain fungi
- What are the 4 basic principles of plant disease control?
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1) Exclusion of the pathogen from where it is unwelcome by competition
2) Elimination or inactivation of the pathogen from where it occurs by antibiosis or hyperparasitism
3) Reduction of the pathogen's inoculum production by induced resistance
4) Cross-protection against the pathogen by a competing non-pathogen, avirulent pathogen, or with pathogen-derived genes - What are the objectives of the 4 principles of plant disease control?
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1) remove or reduce the inoculum
2) reduction in the rate of disease development - By understanding disease development, what is its impact on management decisions?
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By decreasing the disease rate, you:
- reduce inoculum buildup
- reduce over-wintering inoculum
- use resistant host varieties to reduce disease levels
- point of attack: the lag phase! - What is meant by "control" vs. "management", and how do the economic objectives of control relate to this?
- Often control means management which is reduction of economic loss to a manageable level, so cost of control vs return on investment must be looked at
- Describe antagonism/antibiosis, competitive exclusion and parasitism.
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Antibiosis- chemical warfare between beneficial microbes and the pathogen
Competitive exclusion- competition at infection courts and for nutrients
Parasitism- parasites and pathogens of pathogens - Explain the mechanism of hypovirulence.
- Biological control by hypovirulent strains of the same fungus carrying ds RNA fungal viruses
- Explain the mechanism of induced systemic resistance.
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a widespread phenomenon mediated by salicylic acid-dependent signalling cascade that leads to broad-spectrum and long-lasting disease resistance
- induced by local infection by pathogens as well as by plant-resident or plant-associated non-pathogenic microbes (Plant Growth Promoting Rhizobacteria (PGPR) - Explain the mechanism of cross protection.
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plants already infected with a virus are normally protected against infection by a related strain of the virus
- ex: citrus plant infected with mild strain of tristeza virus are protected from the more severe strain - What is the difference between inoculative and inundative control strategies?
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In inoculative control, you put out the biocontrol agent and it spreads naturally.
In inundative control, it must be spread like a pesticide repeatly until control is reached. - What is Uromycladium tepperianum?
- a rust fungus that biologically controlled Port Jackson willow
- How does Tobacco Mild Green Mosaic Virus aid control of Tropical Soda Apple?
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It will cause a typical hypersensitive response in tobacco but a lethal hypersensitive response in TSA after 2 weeks
- plants must be damaged in order for virus to work - What is Bacillus subtilis?
- a bacterium that IB12 is made of that can boost plants' growth while protecting them from harmful fungal infection through competition and antibiosis
- What is IPM and what is the role of chemical control in IPM?
- IPM is the integrated approach of all techniques (preventative, cultural, chemical, mechanical and biological) to reduce pests and disease. For disease mgmt, chemical control is in the form of fungicides and bactericides for the control of pathogens preplant, during crop production or post harvest.
- What are fungicides?
- substances that kill fungi (inhibit fungal growth and/or sporulation). Some will also kill/inhibit bacteria.
- What are fumigants?
- volatile substances used to disinfest areas of certain pests including plant pathogens. most are general biocides
- What types of mode of action are there is fungicides?
- single MOA and multi-site MOA (chloronitriles); benzimidazoles inhibit cell division, dicarboximides inhibit DNA and RNA
- What are the classifications of fungicide activity?
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Protective
Curative which are generally systemic; use should be based on likelihood of plant recovery and economics - What are the mechanics of fungicide resistance and the impact?
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fungi can rapidly develop resistance to fungicides that have single modes of action
- resistance to strobilurins has been documented by many pathogens - What are techniques to avoid fungicide resistance?
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1) Don't use product in isolation- mix or rotate with different classes
2) Restrict treatments applied per season
3) Maintain manufacturer's recommended dose
4) Avoid eradicant use- apply prophylactically
5) Practice IPM
6) Maintain chemical diversity - What are some examples of formulations of fungicides?
- emulsifiable concentrates (EC), wetable powders (WP), water dispersable granules (WDG), dry flowables (DF), dusts (D)
- What are the 5 Rs of effective fungicide use and examples of each?
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- Right fungicide (differ in their range of activity; Oomycete vs true fungus)
- Right rate (too high = phytotoxicity, too low = dev of fungicide resistance
- Right time (best time for greasy spot is June-Jul)
- Right method (conventional system vs. ultra-low system)
- Right place (downy mildew- underside of leaves) - What is FRAC?
- Fungicide Resistance Action Committee
- What is the breeding triangle?
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- source of desired gene
- host or target cultivar or plant
- ability to transfer gene character - What is the difference between self pollinated and cross pollinated crops?
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self pollinated- pollen moves to the female part of the same flower, or to another flower on the same individual plant (wheat, beans, tomato, rice)
cross pollinated- pollen is delivered to a flower of a different plant (corn, squash, clover) - What breeding methods would be employed for self pollinated crops?
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- Pure line (single target plant)
- mass selection (select many plants, used for sustainable production)
- pedigree selection
- bulk method (hybrids grown in bulk)
- backcross method - What breeding methods would be employed for cross pollinated crops?
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- mass selection
- backcross method
- hybrids
- recurrent selection (selection for desired genotypes) - What is pedigree selection?
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- directed hybridization to create variability
- need to keep strict records
- leads to homozygosity
- used to combine desired characters from different parents to creat superior cultivar - What is the backcross method in breeding?
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- transfer of one or few genes
- recurrent backcrosses are made
- most important in getting disease resistance - What are hybrids?
- cross inbred lines and clones that require easily made seeds
- What steps make up the Diagnostic Check List?
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- Plant name
- Obtain a good sample
- Gather background info
- Examine plant
- Consult literature
- Diagnosis - How do you decide which dagnostic techniques to use?
- depends on the suspected pathogen group; use symptoms as guide
- What are general techniques for detecting fungal pathogens?
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1) direct macroscopic observation
2) direct microscopic observation
3) moist chamber to induce sporulation
4) isolation on media to produce structures
5) ELISA
6) Immunofluorescence
7) PCR
8) RFLPs - What are general techniques for detecting bacterial pathogens?
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1) direct macro
2) direct micro
3) isolation
4) identification by conventional tests
5) identification by nutritional test kit
6) identification by fatty acid analysis
7) ELISA
8) Immunofluorescence
9) PCR - What are general techniques for detecting viral pathogens?
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1) direct macro
2) direct micro
3) transmission- indicator plants
4) serology- ELISA
5) PCR
6) dsRNA