Exam 2 Flashcards
What are some examples of important plant fixed physical defenses?
Lignin, Cuticle, Trichomes
How might trichomes provide defense?
Trap and impale an insect
What is a phytoanticipan?
– Plant secondary metabolites with anti-microbial or anti-herbivore properties
– Formed before pest/pathogen attack!
– 4 Main Classes:
Phenolic Compounds, Saponins, Alkaloids, Terpenoids
What is the functional role of nicotine for plants that produce it?
Blocks insect’s acetylcholine receptors (overstimulation, paralysis and death)
How do some insects/pathogens overcome or even exploit these fixed chemical defenses?
Some insects are immune to the toxins, so they consume them and then use them in their bodies to deter their own predators
What are some examples of induced structural defenses?
Cork layers, Callose Papillae, Abscission Layers
How is a phytoalexin different than a phytoanticipan?
Phytoalexins are Produced in response to non-specific pathogen/insect signals
or wounding
What is the hypersensitive response and what pathogens is it useful against?
Triggered by specific gene for gene interaction, Causes localized death of plant cell(s) and production of antimicrobial compounds. Useful against BIOTROPHIC pathogens. Retreats but destroys everything useful to (biotrophic) enemy
What are some potential triggers of systemic acquired resistance?
Being exposed to pathogens or artificial chemical stimuli
why isn’t systemic acquired resistance activated all the time?
It needs an initial infection
What is a biological control?
use of natural enemies to suppress pest populations
What are main types of natural enemies for insects, and what are the differences between them?
Pathogens: organisms that cause disease to another
Predators: animals that consume other living things
Parasitoids: an insect that spends its larval stage in or another organism (aka host)
What are the 4 kinds of applied biological control we discussed?
classical, augmentative, neo-classical, conservation
Classical bio control definition and pros and cons
Classical: Introduction of new natural enemies (establishing permanent pop.)
PRO: Can be very effective (long-term)
CON: Dealing with non-native species risks invasion
Augmentative bio control definition and pros and cons:
Augmentative: Periodic release of natural enemies (establishment is not the goal) - VERY successful is greenhouses, mixed results in the field
PRO: Dealing with natural enemies that are already present-reduced risk of non-target or subsequent invasions
CON: Fighting against the ecological pressures that are already in place to keep natural enemy populations low: difficult to know how many individuals to release or if they will have an effect
Neo-Classical bio control definition and pros and cons
Neo-classical: Target native pest with non-native species - MOST SUCCESSFUL
PRO: Totally new associations will be more devastating to pests because the pest has not coevolved with its enemies
CON: Over time, coevolution will theoretically dampen this effect
Conservation bio control definition and pros and cons
Conservation: Using management practices to increase or enhance control by natural enemies already in the environment
PRO: can provide temporary diversity to support beneficials throughout the season
CON: can accidentally outbalance the predator / prey
Define the inoculative versus inundative releases (both augmentative) and when they might be used.
Inoculative: release fewer individuals and expect population growth via reproduction (i.e., several generations across the season) (use when you want the predator around a little longer)
Inundative: release millions on individuals (no reproduction expected), just one generation of targeting the pest (use when you don’t want the predator sticking around as long)
Generalists versus specialists and the differences between an organism’s physiological range and ecological range
Generalists: predators that target many species
Specialists: predators that target a specific species
Physiological range: all potential hosts that can be consumed and support growth and reproduction
Ecological range: hosts that are actually consumed in natural ecosystems
EX: It is physiologically possible for B. communis to use A. monardae as a host, but ecologically improbable cause of where they are
Define what GMOs are (not just what GMO stands for).
An organism whose genome has been altered in a specific way by genetic engineering
EX: a tomato expressing a gene from fish OR
corn that produces! dsRNAs targeting corn rootworm
Understand the differences between genomes, chromosomes, and genes.
Genome: the language cells pass to offspring
Chromosome: a threadlike structure of nucleic acids and protein found in the nucleus of most living cells, carrying genetic information in the form of genes
Gene: a distinct sequence of nucleotides forming part of a chromosome
Understand the differences between genetic changes created through selective breeding and genetic modification.
Selective breeding: choosing parents with particular characteristics to breed together and produce offspring with more desirable characteristics
Genetic modification: transferring a piece of DNA from one organism to a different organism
Understand the different types of traits found in different GMO varieties
EX: non-browning in food,
insect resistance in corn for ethanol or livestock feed,
herbicide tolerance
Understand the importance and utility of new tools such as RNAi and CRISPR
RNAi reduces gene expression at the mRNA level (knockdown), while CRISPR completely and permanently silences the gene at the DNA level (knockout)
Understand how GMOs are created (generally).
“Cut and stitch method” - DNA fragments are cut and combined in sections
What are the three dimensions of plant diversity and how can they be used to control insect pests?
Temporal: Primarily impacts pest diversity, abundance, and persistence
Spatial:
Smaller scale: within a field, different plots or rows
* Trap plants: attract pests away from main crop
* Push-pull : one crop deters pests, while the other attracts them
* Banker plants- provide resources for natural enemies
Larger scale: between fields, landscapes = less control and stronger effects on mobile species
Plant genotypes/phenotypes: Traits that encourage natural enemies
What is a trap crop? The push-pull system? A polyculture?
Trap crop: attract pests away from main crop
Push-pull system: one crop deters pests, while the other attracts them
Polyculture (intercropping): the planting of multiple plant species or varieties to garner ecological benefits that make the habitat less suitable for pests
What is the resource concentration hypothesis and the enemies hypothesis and how does each affect insect pests?
Resource concentration hypothesis: Predators and parasites are more effective at controlling herbivore populations in diverse habitats or plant communities because, diverse plant communities support a diversity of herbivores. Provides steady stream of prey for predators
Enemies hypothesis: Less diverse plant communities support less diverse insect communities, which limit the abundance of natural enemies
What role do chemical signals play in pest damage?
can prevent specialists from finding host plants
Understand the differences between genotype and phenotype.
Genotype: genetic characteristics
Phenotype: emergent or functional characteristics
(Genotype leads to phenotype)
What is the definition of resistance?
a heritable decrease in the susceptibility of a pest to a pesticide
Understand and contrast the different mechanisms through which insects can become resistant (e.g. target site, behavioral, physiological)
Target site: Bt Cry proteins bind to specific proteins in the insect gut -> insects evolved to have different shapes of these proteins in their gut so Cry can not bind
Behavioral: Avoidance of the control method.
EX: cockroach borax poison baited with sugar to get the roaches to eat the poison -> roaches evolved to avoid glucose.
Physiological resistance: the ability of an insect population to survive exposure to a concentration of insecticide that would normally result in complete kill
How do pests evolve resistance to insecticides, i.e., what are the necessary steps?
- Genetic variation/phenotypic variation
- Differential survival
- Inheritance
(repeat)
What circumstances promote resistance? How can it mitigate the evolution of resistance?
- Tactics that have strong impacts on survival impose stronger
selection - High resistance allele frequencies prior to selection
- Low cost of carrying resistance alleles
- When resistant alleles are dominant
- Monogenic resistance phenotypes
- When pests have short generation times and high fecundity
What are the assumptions of the high dose/ refuge strategy for resistance management? Are they likely met?
Assumption #1: resistance is recessive
Assumption #2: resistance alleles are rare (<0.1%)
Assumption #3: mating is random within fields and occurs across fields
(not likely met)
What is a vector?
The sucking insects that spread mostly viral and cell-wall-less bacterial pathogens
Understand the co-evolutionary dynamic that occurs between plant pathogenic microbes and their insect vectors.
Ex: A bug with a long sucker antenna infects a deep flower, so the flower gets deeper and the insect’s antennae get longer and they go back in forth with this for generations
Compare and contrast the characteristics of a persistent and a non-persistent vector
Persistent vector
– Virus must circulate or propagate through insect to be re-injected
– Several hours required before virus can be transmitted after feeding (latent period)
– Insect retains virus for days/weeks (Some can even pass to offspring!)
Non-persistent Vectors
– Often stylet borne
– Pathogen acquired quickly by vector
– Can be passed to new host immediately
– Vector loses ability to transmit pathogen within minutes
Understand how a pathogen benefits from influencing vector behavior and how that can differ depending on if it is a persistent vs. a non-persistent vector.
- Pathogens with persistent vectors helped those vectors at all stages
- Pathogens with non-persistent vectors attract vectors to infected plant but don’t want them to stay long (pull-push strategy)
Know the strict definition of a biocontrol agent of pathogens
Use of living organisms to control pests or pathogens
What are some examples of biocontrol agents and what are examples of their modes of action?
Bacteria: Competition (multiple)
Fungi: Hyper-parasitism, induction of plant defenses, antagonism
Pathogens: Reduction of Plant Abiotic Stress
What are some pros and cons of biocontrol of plant pathogens compared to chemical sprays?
PROS:
Less toxic
Pest resistance development is rare
Consumer acceptance
CONS:
Harder to understand how they work (and why they can fail to work)
Living = lower shelf life
Tend to be more specific to plant/pathogen
Know the definition of a “suppressive soil” and some ways that they have formed.
Disease Suppressive Soils: Soils which have an innate ability to suppress soil-borne plant disease
Formed by
“Take-all decline”: Soil develops suppressive characteristics as bacteria builds in the soil and disease then decreases
Composts
Increase microbial mass
Why might long term monoculture be good in some very specific situations?
It can (rarely) lead to take-all decline which is when soil develops suppressive characteristics as bacteria builds in the soil and disease decreases
Know how the use of compost potentially relates to disease suppression
– Many pathogens killed by heat in composting process
– Saprophytes tolerate it more effectively
– Also plant benefits from nutrients and water retention
How can diversity of crops through time be used to manage pathogens?
Reduction of soil and residue borne pathogens
How can diversity of crops through time be used to prevent the loss of plant resistance?
Leads to more non-hosts plants
What is the difference between intercropping and multiline?
Intercropping: Mixtures of different crop species
Multiline: Mixtures within crop species
What are some potential mechanisms of how intercropping lowers disease pressure?
– Replacement Type
– Addition Type
Which pathogen types have resistance issues and which do not
- Fungi
Fungicides (resistance issues exist) - Bacteria
Antibiotics and copper (resistance issues exist) - Nematodes
Nematicides (no documented field resistance) - Viruses
No direct chemical controls available!
The difference between discrete vs. stepwise resistance patterns
discrete = 2 peaks on grapgh (often “no” fitness cost)
stepwise = several in concession (some fitness cost)
Mechanisms of resistance
- Alteration of target site
- Overexpression of target protein
- Active efflux of fungicide
- Metabolic breakdown of fungicide
Resistance management strategies
- Practice Integrated Pest Management
- Restrict Use
- Apply Correct Rates
- Rotate MOA
- Use multi-site MOA
What is the meaning of “cross-resistance”?
Cross-Resistance: pathogen that evolves resistance to one fungicide typically also becomes resistant to other fungicides with same mode of action
What is the technical definition of an invasive species
1) a non-native (or alien) to the ecosystem under consideration and
2) whose introduction causes or is likely to cause economic or environmental harm or harm to human health.
What are the ecological/evolutionary theories that attempt to explain what makes different types of organisms (plants, pathogenic microbes, insect herbivores) successful invasive species?
- Lack of predators
- Outcompete native species for food
- Lack of co-evolutionary history
What are the basic benefits to the plant provided by rhizobia (BNF, biological nitrogen fixation)?
Little nitrogen fertilization needed to grow legumes
Rhizobia add nitrogen to soil for next crop (Nitrogen Credit)
What are the pros and cons of using rhizobia vs conventional fertilization?
PROS: Less runoff problems with rhizobia
CONS: Rhizobia more affected by soil conditions
How do mycorrhizae benefit the plants they associate with?
– Provide micronutrients (P especially) and water to plant
– Also help defend against pathogens
– Plant provides fixed carbon (food)
How do conventional agricultural practices affect natural mycorrhizal colonization?
Soil Nutrients?
– Phosphate (P) addition to plant can reduce mycorrhizal colonization
Tillage?
– Generally bad for mycorrhizae
Pesticide?
– Fungicides inhibit mycorrhizae
Cover Crops?
– Fallow periods and winter can reduce mycorrhizal inoculum by 30-40%
– Using mycorrhizal compatible cover crops in no-till systems can maintain viability
What are the pros and cons of using plant resistance to manage plant disease compared to other management techniques?
PRO:
- Easy!
- Environmentally Friendly
- Cost Effective (if disease is present)
CON:
* May not be available!
* May not be highest yielding variety
* May not be as resistant to other pests/pathogens
* Less Flexible
* Must know potential problems before planting
* May fail over time!
Compare horizontal and vertical resistance
Horizontal:
* Resistance is typically relatively durable!
* Hard to breed for!
Vertical:
* Resistance is relatively unstable!
* Relatively easy to breed for!
What types of plant defenses tend to be most “durable” in the long term?
– The more specific the mode of action, the less durable the resistance
What types of plant defenses might you not want in a crop?
Fixed, Horizontal
