Final Flashcards
<p>What are other names for the second class of ascomycetes?</p>
<p>Fungi Imperfecti
| Deuteromycetes</p>
<p>What are some reasons for the same species having different names?</p>
<p>Classified based on macroscopic features and reproductive features
Classified based on teleomorphic/anamorphic (sexual/asexual stages)</p>
<p>What are the types of fruiting bodies in ascomycetes?</p>
<p>Conidiophores (tree-like)
Acervulus (disk)
pycnidia (flasks)</p>
<p>Septoria create</p>
<p>pycnidium</p>
<p>Colletotrichum create</p>
<p>acervulus</p>
<p>Alternaria create</p>
<p>conidiophores</p>
<p>Botrytis creates</p>
<p>conidiophores</p>
<p>Verticillium creates</p>
<p>conidiophores and microsclerotia</p>
<p>Fusarium creates</p>
<p>conidiophores and clamydospore</p>
<p>What is the conidial life cycle?</p>
<p>Germination
Penetration
Sporulation</p>
<p>Pycnidia</p>
<p>flask-shaped
bear conidia
typically ooze conidia out during rain--slash dispersed
e.g. seportia leaf spots (necrotrophic)</p>
<p>Ascervulus</p>
<p>flat/disk shape embedded in plant tissue
frequently cause antracnose diseases (hemitrophic)
produce conidia</p>
<p>Conidiophores</p>
<p>tree-like
typical pathogen is facultative saprophyte
e.g. molds, vascular wilts, root/crown rots, leaf spots</p>
<p>Examples of alternaria</p>
<p>leaf spots early blight gray mold verticillium/vascular wilt (unilateral wilting)--e.g. Dutch Elm disease Fusarium rots storage molds</p>
<p>fusarium rots</p>
<p>opportunistic--can live endophytically, does well as saprophyte
e.g. dry potato rot, corn ear rot, wheat head blight
three types of asexual spores: macronidia, micronidia, clamydospores</p>
<p>Basidiomycota</p>
<p>club fungi</p>
<p>What are Basidiomycota cell walls made of?</p>
<p>Chitin</p>
<p>Sexual reproduction for Basidiomycota is carried out with what structure?</p>
<p>basidiophores</p>
<p>What kind of nuclei do Basidiomycota have?</p>
<p>dikaryotic (2 haploid nuclei)</p>
<p>What major pathogen groups are caused by Basidiomycota?</p>
<p>root rots and web blights (sterile fungi)
root and heart rots of forest and fruit trees
smuts of cereals
rusts of grasses, pines, rose family, coffee, etc.</p>
<p>What are some examples of root rots and web blights caused by Basidiomycota?</p>
<p>-Rhizoctonia: causes many diseases; mostly soil-borne; 90 degree hyphae branching; no asexual spores
-turf diseases: red thread (Laetisaria fuciform), gray snow mold (Typhula blight)</p>
<p>What are some examples of root and heart rots of forest and fruit trees caused by Basidiomycota?</p>
<p>-Armillaria root rot: facultative parasite; basidiocarp is a mushroom; transfers via root contact or rhizomorphs; attacks oak, grape, pine, fruit trees; colonizes dead wood
-heart rots: decay of older, central wood; caused by large fleshy fungi; basidia produced on basidiocarps (conks or mushrooms)</p>
<p>Rhizomorph</p>
<p>Aggregated mycelium strands
| Grow along roots and from root to root</p>
<p>How many basidiospores are produced in one conk?</p>
<p>~30 billion a day</p>
<p>What are some examples of cereal smuts caused by Basidiomycota?</p>
<p>-loose smut of barley
| -common corn smut (infect anywhere, not just seed; delicacy in Mexico)</p>
<p>What are some general characteristics of smuts?</p>
<p>obligate parasites
2 spore types: teliospores (overwinter), basidium (infective)
fungal teliospores replace normal seeds of plant</p>
<p>What are some examples of rusts caused by Basidiomycota?</p>
<p>puccinia graminis: wheat stem rust; infects wheat and barberry</p>
<p>What are some general characteristics of rusts?</p>
<p>obligate parasites attack leaves and stems produce pustules usually don't kill, just weaken many produce 5 types of fruiting bodies</p>
<p>What is the life cycle of rusts that produce 5 types of fruiting bodies?</p>
<p>teliospores --> meiosis --> basidium --> basidiospores --> spermagonium (infect new host) --> spermatia --> aecium (grows through host tissue) --> aeciospores (distributed through air to new host) --> uredium --> urediniospore (repeating stage) --> telium (overwinters) --> teliospore</p>
<p>Heteroecious</p>
<p>Pathogen requires more than two different plant hosts to complete life cycle</p>
<p>What are the six major groups of bacterial plant pathogens?</p>
<p>Pectobacterium (Erwinia): soft rots
Pseudomonads: many, including ice + bacteria
Xanthomonads: leaf spots, blights; often seed associated
Agrobacterium: crown gall
Clavibacter and Xyella: vascular wilts
Candidatus Liberibacter: obligate phloem inhabitants</p>
How much annual damage are fungal pathogens responsible for?
70% of all diseases, destroys 125 millions tons of top five food crops annually
Phytophthora infestans
Late blight (potatoes, tomatoes) Oomycete
Who is the father of plant pathology?
Anton DeBary
Observed spores of potato blight; experimentally reproduced symptoms
What are Koch’s Postulates?
- The suspected causal organism must be constantly associated with the disease.
- The suspected causal organism must be isolated from an infected organism and grown in pure culture.
- When a healthy susceptible host is inoculated with the organism from pure cultures, symptoms identical to those of the original disease must develop.
- The same pathogen must then be re-isolated from plants infected under experimental conditions.
What are some exceptions to Koch’s Postulates?
(1) Some pathogens have a latent period (presence may not always result in disease)
(2, 4) Some pathogens are obligate biotrophs (i.e. cannot be grown in artificial culture)
What is the definition of disease?
The injurious alteration of one or more physiological processes in a living system caused by the continuous irritation of a primary causal factor(s)
What ingredients are necessary for disease to occur?
- pathogenic agent(s)
- host must be susceptible to the agent(s)
- environment conducive to interaction of pathogen and host
What is the definition of a symptom?
terms that describe a diseased condition; a plant’s response to a disease that reflect the physiological function that is disrupted/impaired
e.g. necrosis, rot, canker, gall, curl, damping off, dwarfing, wilt
What is the definition of a sign?
an observed pathogen structure associated with a symptom;
e.g. fungal: spore, pustule; bacterial: streaming; nematodes: cysts
What are biotic causal agents of plant disease?
Fungi (and oomycetes) Bacteria Viruses Nematodes Phytoplasmas Viroids Parasitic Plants
What are abiotic causal agents of plant disease?
Air pollutants (e.g. ozone, sulfur dioxide)
Chemical imbalances or toxins
Sunburn
Herbicides
Excess/Low trace elements (e.g. calcium, boron)
Lightning
What is the difference between fungal and bacterial leaf spots?
Fungi more round; bacterial take on shape of leaf bordered by vein
How can one tell that a plant’s symptoms are abiotic?
- typically no spread observed
- regular distribution or uniform damage
- clear lines demarcating healthy vs. damaged tissue
- more than one plant species may be affected
- linear stripes
- more common near edges of host population
How can one tell that a plant’s symptoms are biotic?
- symptoms arranged irregularly
- transition from injured to healthy is diffuse
- there are varying sizes and stages of severity (indicative of a continuous process)
What are some population-level patterns that biotic symptoms cause?
Random: observed with seedborne inoculum, or if inoculum source is very far away
Aggregated/Contagious: indicates random distribution followed by disease; foliar diseases
Patch: indicates root infecting pathogen; often delimited by topography or soil type
What is the definition of a primary symptom?
Occurs at site of infection
e.g. root rots, leaf spots, blights, galls, cankers
What is the definition of a secondary symptom?
Occurs at site distant from the primary symptoms and usually later in time
e.g. above ground symptoms of root rot, crown rot, vascular wilt, nematode damage
What are some primary and secondary symptoms of root rots?
Primary: lesions on roots
Secondary: foliar chlorosis, stunting root, top dieback
What are some primary and secondary symptoms of wilts?
Primary: vascular discoloration
Secondary: unilateral wilt of leaves, defoliation, roots remain healthy
What are some primary and secondary symptoms of leaf spots?
Primary: necrotic lesions
Secondary: chlorosis, defoliation
What are some primary and secondary symptoms of stem cankers?
Primary: canker, sunken lesions
Secondary: distal leaf dieback (because lesions breaks flow of nutrients)
What are some laboratory tests used to identify a pathogen?
- microscopic observation of signs
- incubated diseased tissue in moisture
- cultured disease tissues in petri dish
- biochemical tests: serology, DNA hybridization
- chemical tests (for abiotic causes): pH, nutrient deficiency
- Koch’s postulates (for new disease)
Secondary Inoculum definition
infectious propagules that were produced by infections that took place during the same growing season; typically asexual, short-lived
Monocyclic disease definition
infection caused by primary inoculum only and have a primary cycle only; soilborne diseases typically monocyclic
Polycyclic disease definition
disease where one to many cycles of infection are initiated by secondary inoculum; many foliar diseases are polycyclic (e.g. powdery mildews, rusts)
What factors address the time required for symptoms to be expressed?
Incubation period
Latent period
Quiescent infections
Incubation period definition
the time between infection and symptom expression, typically regulated by temperature
Latent period definition
the time between infection and new spore production; i.e. generation time, spore development; governs the speed of increase in polycyclic diseases
Quiescent infection definition
inactive, symptomless, microscopic infections
Symbiosis definition
close, long-term interaction of two or more species
What are the main types of symbiosis?
mutualism
parasitism
commensalistm
Mutualism definition
relationship that benefits both partners
Parasitism definition
relationship in which one organism lives in or on another living organism, obtaining from it part or al of its organic nutriment, commonly exhibiting some degree of adaptive structural modification, and causing some degree of real damage to its host
plant pathogens are a subgroup of parasites, but only when expressing symptoms
Commensalism definition
relationship that benefits one partner and neither harms nor benefits the other
What are the major nutritional relationships (trophic levels)?
necrotrophs
biotrophs
hemiobiotrophs
Necrotroph definition
pathogen that kills a host and feeds on dead tissues; can be generalists or host-selective
Biotroph definition
pathogen that feeds on living host tissue
Hemiobiotroph definition
pathogen that grows initially as a biotroph but eventually kills the host tissue
Obligate parasite definition and examples
organisms that can grow only as a parasite in association with its host plant; usually cannot be grown in artificial culture
e.g. rusts, powdery mildews, downy mildews, viruses, phytoplasmas
Facultative parasite definition and examples
organisms that are normally parasitic but are capable of being endophytic, or saprophytic; usually can be grown and maintained in artificial culture
e.g. smuts, leaf spotters, many root rotters, most bacterial pathogens
Facultative saprophyte definition and examples
organisms that are normally saprophytic but are capable of being parasitic; easily grown and maintained in artificial culture
e.g. crown gall bacterium, wood decay fungi, damping off fungi, fruit rotters, storage mold
Obligate saprophyte definition and examples
organisms that are only able to utilize nonliving organic matter (non-pathogenic)
e.g. wine and beer yeasts, bread and cheese molds
Biotroph definition
an organism that obtains nutrients from living host cells only, and is able to reproduce only as long as its association with living cells is maintained; usually do not cause death of host
e.g. rusts, smuts, mildews, viruses
How do fungi, bacteria, viruses, and nematodes enter their host?
Fungi: active or forceful penetration
Bacteria: active penetration
Viruses: passive penetration
Nematodes: active penetration
What are some examples of enzymes used by fungal pathogens to gain entry into their host?
Cutinases (break down waxy layer) Cellulases (break down cellulose fiber) Pectinases (break down middle lamella) Hemicellulases Lignases (lignin strengthens cell wall--very tough) Lipases Proteases
Thigmatropism definition
sensory mechanism used by some fungal pathogens to “feel” the stomatal opening
Describe how a fungal pathogen might infect a host via appressoria
Hyphal ends swell to produce an appressorium (infection cushion) at one end –> presses hard against cell wall to create leverage for penetration peg to enter host
Papilla definition
thick deposit of callose deposited by nucleus in front of a penetration peg in attempt to repair damaged wall
What are other names for oomycota?
Egg fungi
Water molds
Oomycetes
What are the asexual and sexual spores of oomycetes?
asexual: sporangia and zoospores
sexual: oospore (via antheridium and oogonium)
What are some important soilborne oomycete pathogens?
Pythium damping-off
Pythium blight of turf
Phytophthora root rots (Phytophthora cinnamomi)
What are some important foliar oomycete pathogens?
Late blight of potato/tomato
Sudden oak death (Phytophthora ramorum)
Downy mildews
What conditions does Pythium damping off favor?
Cool and wet soils
What are some characteristics of Pythium blight of turf, and what conditions does it favor?
Opportunistic
Colonize dying plant material
Prefers warm weather and grass crowns/thatch layer submerged underwater for certain period of time
Plants susceptible if stressed, too much N
Thatch definition
layer of dead plant matter on tope of soil
What are some characteristics of Phytophthora cinnamomi?
Infects over 5000 species
Originated in Asia (high genetic diversity); clonal population in rest of world
First symptoms: red/brown discoloration, darkening of bark
Secondary symptoms: leaf curl
Oospore definition
long-lived resting (sexual) spore of oomycote fusion of antheridium and oogonium germinates to become zoosporangium not easily dispersed diploid cell walls made of cellulose
Homothallic definition
self-fertile, an individual is both male and female
Heterothallic definition
different isolates required for oospore production (individual is male or female)
What is one symptom of sudden oak death (Phytophthora ramorum)?
red/brown, expanding canker
What are some characteristics of oomycote asexual spores?
sporangium produces zoospores
sporangia more common in foliar–spread via wind
zoospores require water for movement–spread in soil
Ascomycota definition
sexual spore: ascospore
asexual spore: conidia
Haploid
Cell walls made of chitin
Ascospore definition
Produced in ascus (sac)
released in spring/fall
usually contained in a fruiting body (ascocarp or ascoma)
What are the different types of ascocarps?
Chasmothecium (spherical)
Perithecium (flask-shaped)
Apothecium (disc-shaped)
What are some diseases caused by Ascomycota that rely heavily on their sexual phase (ascospore)?
Powdery mildews Apple scab Eastern filbert blight White mold Tar spot of maple
What are some characteristics of powdery mildew ascomycota pathogen?
Polycyclic
Obligate biotroph
Primary inoculum: ascospores from spherical chasmothecium, or conidia from infected leaf buds (depends on pathogen species)
Secondary inoculum: Conidia (powedery spores)
What are some characteristics of apple scab ascomycota pathogen?
Polycyclic
Facultative saprophyte
Primary inoculum: ascospores in perithecium
Secondary inoculum: conidia
What are some characteristics of Eastern Filbert Blight ascomycota pathogen?
Monocyclic
Obligate biotroph
Produce ascospores only in perithecium embedded in stroma
Has 1.5 year latent period and 14 month incubation period
What are some characteristics of white mold ascomycota pathogen?
Monocyclic
Facultative saprophyte
Produce ascospores only in apothecium from sclerotia (asexual survival structure)
What are some characteristics of tar spot on maple ascomycota pathogen?
Only produces ascospores
“black tar” is immature apothecia born on leaf surface
What is the largest group of pathogens studied in this class?
Ascomycota where the asexual spore stage plays a prominent role
What are other names of ascomycota whose prominent stage is asexual?
Fungi Imperfecti (often have no sexual stage) Deuteromycetes
What is a teleomorphic name?
a name based on the sexual stage
What is an anamorphic name?
a name based on the asexual stage
What are the types of asexual fruiting bodies of ascomycetes and what do they produce?
Conidiophores
Ascervulus (disk, embedded): produce conidia; typically cause “antracnose” diseases
Pycnidia (flasks): produce conidia
What are some characteristics of Seportia leaf spots ascomycota pathogen?
spread in warm, wet whether or when too much N
produces oval spots–similar to bacterial leaf spot, but more angular (fill in between veins)
What is one obvious symptom of Verticillium wilt?
unilateral wilting (one side of leaf is more severe than the other)
What are some characteristics of Dutch Elm ascomycota pathogen?
Synnema (aggregated conidiophores) spore
Spread by bark beetles
What are some characteristics of Basidiomycota?
Club fungi Septate hyphae Dikaryotic (paired haploid) Chitin cell wall Sexual reproduction: basidiospores produced externally
What are the main pathogen groups of basidiomycota?
- Root rots and web blights (“sterile fungi”)
- Root and heart rots of forest and fruit trees
- Smuts of cereal
- Rusts of grasses, pines, rose family, coffee, etc.
What are some characteristics of root rot and web blight basidiomycota pathogens?
Facultative parasites
Rarely produce teleomorph
Produce sclerotia for overwintering (but generally no asexual spore)
What are some examples of root rot and web blight basidiomycota pathogens?
Rhizoctonia (many diseases, mostly soilborne; hyphae at right angles)
Red thread turf disease (Laetisaria fuciform)
Gray snow mold turf disease (Typhula blight)
What are some characteristics and examples of rots of trees basidiomycota pathogens?
Facultative parasites
e. g. Armillaria root rot: basidiocarp is a mushroom; spreads via root contact (rhizomorphs); large host range; colonizes dead wood; world’s largest fungus
e. g. heart rots: decay central wood; basidia produced by basidiocarps (conks or mushrooms); can produce 30 billion spores per conks per day
What are some characteristics of smuts basidiomycota pathogens?
Obligate parasites
“Replacement diseases”–teliospores replace seed of plant
teliospores overwinter –> germinate to form basidium bearing basidiospores
What are some characteristics of rusts basidiomycota pathogens?
Obligate parasites
Attack leaves and stems
Produce pustules through epidermis
May produce up to 5 types of fruiting structures (macrocyclic); some only produce teliospores and basidiospores (microcyclic); some produce only urediniospores (asexual)
autoecious definition
complete life cycle on a single host
heteroecious definition
require two different plant hosts to complete life cycle
e.g. Puccinia graminis: uredia (repeating, orange), telia (overwinter, black) on wheat (polycyclic); spermagonia and aecia (each haploid on opposite leaf sides –> grow through tissue and combine to become 2n) on barberry
virus definition
obligate intracellular parasite; non-cellular life form
consists of nucleic acid (virion)–RNA or DNA–and a protein coat (capsid)
How do viruses multiply inside of living organisms?
By hijacking the biosynthetic machinery (ribosomes) of the host
What was the first virus described, and by whom?
Tobacco mosaic virus, by Dmitriy Ivanovsky and Martinus Beijerink
What are the main components/functions of a virus?
DNA/RNA replication
cell to cell movement
RNA encapsidation
How many viruses are in one cubic centimeter of seawater?
10^6-10^9
How complex is the metagenome of viruses relative to cellular organisms’ metagenome?
they are comparable
What type of virus is the most common?
ssRNA, especially positive
What is the virus life cycle?
Invasion Genome uncoating, expression, and replication Particle (virion) assembly Cell to cell movement Systematic transport through phloem Plant to plant transmission
What is the general path of infection of a virus through a plant?
travel downwards from point of infection–via phloem–then upwards, and then throughout
What are ways that a virus is transferred between plants?
Vegetative propagation Grafting Mechanical transfer of sap Seeds Pollen Mite, nematode, and fungal vectors *Insects (most common)
What is non-persistent virus transmission?
“stylet-born”; “test probe” into epidermal cell; frequent and short duration
What is persistent virus transmission?
“Circulative”; feeding probes are infrequent and of long duration
Does viral disease spread reduce with insecticides?
For persistently transmitted diseases, yes. For non-persistently transmitted diseases, non.
What are typical symptoms of a viral disease?
external: chlorosis in mottled/mosaic patterns
internal: stem pitting, black line symptom (HR at graft union)
What diagnostics can be used for viral pathogens?
Pathogenicity (bioassays using indicator hosts)
Transmissibility (vector transmission assays)
Architecture of the virus particle (electron microscopy)
Antigenic properties of the viral protein coat (ELISA–enzyme-linked immunosorbent assay)
Characterization of viral nucleic acid (PCR, detection of dsRNA in host tissue, genome sequencing)
What is RNA silencing?
A cell defense mechanism against viruses in which cells destroy dsRNAs
What are constitutive host defenses? Examples?
Preformed defenses; Defenses that are always present
Structural: wax cuticle thickness, suberin, stomata shape/activity, trichomes
Biochemical: pre-formed inhibitors (phenolics), tannins, immune receptors (innate immunity–PTI/ETI)
What are induced host defenses? Examples?
In response to an attack
Structural: papillae, abscission layer, gums, cork layer, tyloses
Biochemical: Hypersensitivity (specific), phytoalexins/PR proteins/systemic acquired resistance, anti-microbial enzymes, phenolics
What are phenolic compounds?
Secondary metabolites; pigments, antioxidants, secondary structure (in wood and cork), antimicrobials/antibiotics, attractants (perfumes)
Produced by phenylpropanoid pathway
Compounds include flavonoids, alkaloids, phytoalexins, tannins, anthocyanins, lignin, suberin
What is PAMP?
Pathogen Associated Molecular Pattern
e.g. glagellin, chitin, dsRNA
What is PRR?
Pathogen Recognition Receptors
Part of basal defense and innate immunity
What is PAMP-triggered immunity?
PRRs recognize pathogen molecular patterns (PAMPS) and initiate immune responses, e.g. temporary induction of reactive oxides, hormones, possibly SAR, etc.
What is the zigzag model of defense?
attempted infection –> PTI –> ETS (effector suppressors) –> ETI (effector recognition) –> new effector –> ETI etc.
PAMP Recognition triggers immunity –> pathogen releases effectors to suppress immunity –> plant R proteins recognize effector activities
What are tyloses?
Overgrowths of cells that protrude into the xylem vessels, blocking the vascular system to stop the spread of vascular wilt pathogens; allows other parts of water transport system to function
an induced structural defense
What are phytoalexins?
Antimicrobial compounds synthesized in healthy cells near to an infection site after pathogen attack
an induced biochemical defense
Why do so many leaf spots have a typical maximum size?
local induced structural and biochemical defenses restrict lesion size
What two groups do most resistance terminology fall into?
Non-race specific (PAMP-triggered immunity/PTI, quantitative, basal resistance, durable)
Race-specific (Effector-triggered immunity/ETI, hypersensitive reaction, R-gene, less durable)
What is the gene-for-gene model?
the product of a singel gene in a host specifically recognizes the product of a gene in the pathogen, resulting in incompatibility, or resistance, which often involves HR/programmed cell death
Host has R gene (“recognizer gene”) imparting resistance
Pathogen has Avr gene (“defeated” effector); a defeated effector is typically dominant
How many races can a certain number of host cultivars, each expressing a different R gene, yield?
2^(# of cultivars)
e.g. 3 cultivars can yield 2^3 = 8 races
What is the relationship between Victoria blight of oats and crown rust?
They are linked: resistance to one imparts susceptibility to another
What are the phases of a polycylic epidemic?
Exponential
Logistic
Terminal
What is the exponential phase of polycyclic disease?
when the speed of increase is limited by the supply of pathogen propagules; disease is increasing rapidly but the overall amount of pathogen is still small
Relative speed of increase is highest at this stage.
What is the logistic phase of polycylic disease?
when the speed of increase is most limited by the environment
The absolute speed of increase is the highest at this stage.
What is the terminal phase of polycylic disease?
when the speed of increase is limited by the declining amount of non-infected host tissue; much damage is done in this phase
What is the best way to manage a polycyclic disease?
By managing its speed
What happens when a sanitation method is used to control a polycyclic pathogen?
Spread is only delayed
How effective is the race-specific R-gene approach of resistance compared to sanitation in polycylic disease?
Their effects are equivalent; after the introduction of an R-gene, another race typically arises later via mutation
What are two ways to measure disease?
Incidence: proportion of diseased units (e.g. leaves, plants, fields) to total number of units
Severity: Proportion of plant tissue diseased relative to total susceptible tissue
How do you calculate the absolute speed at which a disease spreads for a polycylic disease?
absolute speed = potential infection rate, r * amount of contagious tissue * amount of healthy tissue
How do you calculate the absolute speed at which a disease spreads for a monocylic disease?
absolute speed = potential infection rate, r * inoculum from another season or place * amount of healthy tissue
How can one control the spread of a monocyclic disease?
Reducing the rate of infection
Reducing the amount of primary inoculum
What are the main principles of disease control methods?
Exclusion: certification, quarantine (focus on pathogen)
Eradication: crop rotation, fumigation, therapy (curing with drugs, surgery, heat) (focus on pathogen)
Host resistance: R-genes, polygenic (focus on host)
Protection: chemical paints, sprays, or seed treatments (focus on environment)
Avoidance: planting date/depth, maturity, irrigation method, drainage, humidity (focus on environment)
What are three manageable factors in disease control?
Reduce amount/efficacy of initial inoculum
Reduce the rate of disease development, r
Change the time frame, t
What is a general rule regarding irrigation and fungal root rot and vascular wilt pathogens?
Excessive water early in the season promotes these diseases.
How do rot pathogens target host cells, and what nutrient makes hosts more resistant?
Rot pathogens use enzymes to dissolve the middle lamella between cells. High calcium content in the lamella makes fruits more resistant to decay.
What are the most used chemical crop protectants?
herbicides (51.2%)
Insecticides (25.9%)
Fungicides (19.4%)
What are the main classes of fungicides?
Protectant: chemical barrier that alters the surface environment and protects plants from infection (slow growth, but doesn’t kill spores)
Eradicant: kills the target organism, reduces inoculum
Chemotheraputant: cure infections (drug therapy)
What are the main classes of protectant fungicides?
Contact Locally systemic (move through xylem to treat whole plant system)
What are some strategies for managing resistance in pathogens to chemicals?
Mixtures of fungicides
Rotate chemicals
Limit usage
When are soil fumigants typically used?
on high value crops (e.g. strawberries, peppers, potatos)
When is the eradication method typically used?
for monocyclic diseases
What are some examples of eradication?
Fallow: allowing field to remain uncropped
Ultraviolet light: UV light damages cellular DNA
Thermal inactivation: heat, fire, steam, hot water, sunlight
Chemical fumigation
What are some problems with traditional pesticides?
Environmental persistence
Non-specific/off-target toxicity
Biological accumulation/unhealthy
Development of resistant populations
What is a biocontrol?
An organism that can be introduced/fostered to control a pest population
What are the mechanisms of biocontrol?
Competition
Antibiosis (attacking)
Parasitism
What are some bacterial species that are used as biocontrols?
Bacillus subtilis: hardy in soil; antibiosis, competition, SAR-inducing
Pseudomonas spp. (syringae, flourescens, cepacian)
Agrobacterium radiobactor K84: antibiotics
Streptomyces spp.: forms defensive barrier; foliar spray, soil drench
What fungal species colonizes the roots of a variety of plant species, attacks and subdues other fungi, and enhances plant root growth?
Trichoderma spp.
What type of pathogens is R-gene resistance used for?
Obligate biotrophs (rusts, smuts, eastern flibery blight, downy mildews, powerdery mildews, viruses, nematodes) Facultative saprophytes (hemi-biotrophs) (apple scab, bacterial leaf spots, ascomycete leaf spots, vascular wilts, oomycetes)
How frequently does a defeated effector (AVR) turn back into a stealth effector (avr)? How does this pertain to R-gene pyramids?
~1:10^8 asexual spores will have the necessary mutation
If a host has one R-gene, effector will be defeated fairly quickly. If a host has an R-gene pyramid, the changes of the corrects mutations will be 10^(8*N), where N = # of R genes.
What are some types of gene modification?
Introducing a gene of interest
Silencing a gene
Editing a gene (e.g. CRISPR-Cas9 RR –> Rr)
What is the structure of a nematode?
Invertebrate animal
Unsegmented roundworms
Bilaterally symmetrical
Well developed digestive, reproductive, nervous systems; no circulatory or respiratory systems
What are striae?
The transverse markings of a nematode
What is the cuticle in nematodes?
The outside cover; it is flexible and semipermeable
What is an annule?
The area between striae on a nematode
What is the lateral field of a nematode?
The raised area along the side of a nematode
What are the life strategies of nematode root pathogens?
Ectoparasite (body remains outside of plant tissue) vs. Endoparasite (whole nematode enters plant tissue)
Migratory vs. sedentary (feed in one location only)
What is a root-knot?
a gall that forms on a root and around a nematode, around which eggs are laid
What is a cyst in nematodes?
no gall, nematode pops out of root, eggs retained in body
What are parasitic flowering plants?
Biotrophic angiosperms that obtain water, minerals and sometimes photosynthates from other plants
What is a hemiparasite in relation to parasitic plants?
Green, leafy, photosynthesize
Attack xylem
What are holoparasites in relation to parasitic plants?
unable to photosynthesize, have small leaves
Attack xylem and phloem
What are the types of parasitic plants?
Broomrapes
Dodder
Witchweeds
Mistletoes
What are some characteristics of broomrapes?
Root holoparasites
Economically important in warm areas
Host specific to many crops: crucifers, oilseeds, legumes, potato, tomato, tobacco, sunflower
Symptoms: grow in clumbs at the base of a plant, infecting the roots; shows wilting, stunting, and reduced yield
Control methods: chemical, cultural, biological; control is difficult
What are some characteristics of dodder?
Stem holoparasites
Economically important in warm, dry regions
Host specific to many crops, including forage crops (e.g. alfalfa and cranberries)
Symptoms: yellow vines over plant, infecting stems; show yellowing, stunting, and produced yield
Control: weed or turn under before seeding
What are some characteristics of witchweed?
Root hemiparasites
Economically important in Asia and Africa
Host specific to subsistence crops, rice, millet, corn, and sorghum
Symptoms: wilting, yellowing, stunting, reduced yield; green plants emerge at base of host
Control: weed before seeding, “trap crops” that spur germination
What are some characteristics of mistletoe?
Dioecious stem hemiparasite
Economically important in the US
Host specific to hardwoods and conifers
Symptoms: visible as big clumps, especially when oaks drop their leaves in winter
What are some characteristics of dwarf mistletoe?
Dioecious stem hemiparasite
Economically important in North America
Host specific to many conifers, true firs, lodgepole, southern pines, eastern spruces, Douglas fir, ponderosa, Jeffrey pine
Symptoms: swelling, witches brooms, crown die-back
Control: sanitation, pruning, culling fires, host rotation
What are some problems and solutions facing the future of plant pathologists?
Climate change: buy local
Soil, water quality/availability: drought resistant crops
Monocultures: grow neglected species
Where was our instructor married?
Goodfoot Farm
