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119 Cards in this Set

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Dutch Elm Disease (DED):
the perfect stage scientific name?
Ophiostoma ulmi
ophi= snake, stom= openning...larvae make snake-like pathways/openings
what are synnemata?
Collection of conidiophores fused together to form a stalk, with conidia at the end or on the edges.
(aka coremium)

(**found in DED)
vector for Dutch Elm Disease?
American and European elm bark beetle
obligate or non-obligate parasite:
dutch elm disease?
(can only grow on elms, not artificial media)
Dutch elm Disease disrupts the _____ system of elms, therefor it is a _____ disease.
vascular system

What is the biggest difference between the American and European elm bark beetles relating to disease?
• Native/American; female cuts egg galleries PERPENDICULAR to wood grain
• European (smaller and most common); female cuts egg galleries PARALLEL to the wood grain (larvae tunnel across the grain)
Elms defense mechanisms kill it in the end...what are these defenses?
Tyloses and gums plug vessel element
What are tyloses?
Tyloses occur when a parenchyma cell protoplasm extends into a xylem or tracheid element. It is assumed they contribute to blockage of the vessels and inhibit water flow thus enhancing the wilt process. (Commonly found in many wilt diseases)
Other than the beetle vector, how can Dutch Elm Disease spread?
Root grafts (cephalosporium conidia in vessels pass through roots),
firewood transport
Dutch Elm Disease:
homothallic or heterothallic?
heterothallic (requires compatible mating types)
What DED symptoms are shown on the underside of bark?
Vascular streaking
(brownish blueish streaking)
What is the most effective way to control Dutch Elm Disease?
1. remove dead elms ASAP
2. Store wood barkless
3. Prune flagged sites of trees
What are 2 controls of DED other than sanitation?
fungicide injections (expensive- only used on valuable trees)
What is an autoclave?
an instrument to sterilize equipment and supplies by subjecting them to high pressure saturated steam at 121 °C for around 15–20 minutes depending on the size of the load and the contents
what are the components of growth media?
1. energy source (eg glucose)
2. Amino acids (eg peptone)
3. Vitamins & minerals
4. Agar (holds everything)
5. low pH (inhibits bacterial contamination)
5 types of growth media?
complex (most common)
synthetic [aka defined culture (specific)]
differential (pectic agar)
Common contaminants: which one looks like a pom pom?
Aspergillus sp.
molds; ascomycetes
Common contaminants: which is characterized by columella (looks like a mallet covered with spores)?
Rhizopus stolonifer
black bread mold; a zygomeyete
Common contaminants: characterized by branching growth form?
Penicillium sp.
molds; ascomycetes
scientific name for Oak Wilt?
Ceratocystis fagacearu
(Cerat= horn, so horn cyst of oak)
which oaks are most susceptible to oak wilt?
Red oaks
(a few weeks, compared to years for white oaks)
Oak wilt vector?
Nitidulid (picnic/sap) beetle
Oak wilt is native to ______.
the US.
Describe some symptoms of oak wilt.
Leaf discoloration
Vascular discoloration/tyloses
Pressure pads/cracks (with sweet banana smelling spores!)

Where are you likely to find oak wilt?
"infection centers" radiating from nearby tree via grafting
Scientific name for oak wilt
Ceratocystis fagacearu
plating infected oak wilt material reveals....?
-Dark mycelium
-Boxy, hyaline (crystal-like) endo-conidia produced in chains
-Unique fruity odor
-Pathogen is heterothallic [Perithecia on pads if both mating types present (uncommon though)]
Oak wilt- homothallic or heterothallic?
Pathogen is heterothallic—presence of
perithecia on pads if both mating types are
present (not common)
Main cause of oak wilt spread?
root graft
2 best controls for Oak wilt?
1. Avoid wounding, pruning trees in early spring when most susceptible
2. Sanitation
a. Removal of diseased trees ASAP
b. Trenching to disrupt root grafts (Trench 54 inches or deeper to disrupt root graft)
Scientific name for Chestnut blight?
Cryphonectria parasitica
(memory: chestnut death makes you cry)
chestnut blight originates from _____?
(brought to NY in late 1800's)
Industries impacted by Chestnut blight?
Tanning industry
Nuts (incredible disruption of lives)
Where did chestnut blight have the greatest impact?
Appalachia, where 25% of trees were chestnuts - lost 3-4 billion trees!
Which disease is characterized by cankers?
Chestnut blight

(these can girdle a tree)
Which disease is characterized by pressure pads?
Oak wilt
How is chestnut blight spread?
Infects bark through wound sites, spreads locally to produce a perennial canker,
*Edges of cankers are covered with asexual vase shaped pycnidia (with lots of conidia in a sweet nectar!)which are spread by flying/climbing insects, and wind born ascospores from sexual perithecia .
(pathogen parasitizes many species but has greatest impacts on chestnuts)
Is chestnut blight homothallic or heterothallic?
homothallic (only tree disease covered that does not need compatible mating type)
Which tree disease is a faculatative saprophyte?
chestnut blight (Cryphonectria parasitica)
What is the best control for Chestnut blight?
none are very good. ;(
-Fungicides are unrealistic for natural stands
-No resistance in American Chestnu
**Biological Control; best chance?
1. What is hypovirulence?

2. To what disease is hypovirulence relevant?
1. viral pathogens that weaken the fungus

Double-stranded RNA passed from hypovirulent strains to wild-type via anastomosis (hyphal fusions)
– Drill small holes at edge of canker and inoculate with a compatible HV strain—cover hole with tape
• The dsRNA appears to be from a mycovirus that promotes attenuation…
– Grow slower
– Produce fewer spores
– Allows the tree to “outgrow” the canker

2. May be our last, best hope for saving American
What is a concern with the use of hypovirulence in chestnut blight?
Genetic variability in the fungus may cause severe problems for the long-term usefulness of technique
What 2 lessons did we learn from
Chestnut Blight?
*Perennial-tissue diseases are long-lived and their spread can be very slow, but steady and hard to stop
*Pathogens that appear minor in their native habitats can become very severe when exposed to a new environmen
Scientific name for Ergot?
Claviceps purpure
What is a stroma and what disease does it characterized?
a mass of perithecia (with asci) embedded in a head, supported by a stalk arising from a sclerotium.
Ergot, (and also fusarium head blight, although without the stalk)
(don't confuse with synnemata (conidia head) of DED)
what is a sclerotium and what disease does it characterize?
a compact overwintering mass of hardened fungal mycelium containing food reserves which gives rise to stromata.
*These are the elements that almost resemble a grain and which are poisonous.
symptoms of Ergotism in humans?
”St. Anthonyʼs Fire”
• Alkaloids cause Vasoconstriction which leadsto gangrene

* But has medicinal use too: Used to treat bleeding during childbirth
What medicinal use does ergot have?
Used to treat bleeding
during childbirth
Best control for Ergot?
informed practices such as:
Clean seed
Deep plowing to bury sclerotia (no till not an option)
Mow wild grasses (which harbor ergot)
Crop rotation

(Plants are more susceptible if flowers stay
open longer, e.g. male-sterile barley)

Also Fungicides, but only if cost-effective
What is the scientific name for apple scab?
Venturia inaequali
(memory...johnny appleseed's venture)
What is the range of hosts for apple scab?
All major apple varieties susceptible
All Malus species susceptible (wild, crab, or orchard apples)
How does apple scab affect the apple industry?
lowers fruit quality
can lose a whole crop
most trees heavily sprayed
Best control for apple scab?
MUST spray before, during, or after a rain until all ascospores are discharged
Protectant fungicides will reduce primary infection and lower later spray costs, but still need to monitor throughout season.
*also remove infected leaves
**More organic fungicides are applied per acre to apples than to any other major crop!
What is a biocontrol for apple scab?
antagonistic fungi sprayed
on leaves on ground to suppress
ascospore production—still in infancy. (Spraying still works best so far)
What the biological monitoring program for apple scab?
Apple Scab Computer software:
•Monitors weather data, temp, rainfall, humidity, & predict using models
Scientific name for powdery mildew?
Oidium (asexual) or Spharotheo monilioides

(mildew sounds a bit like moniloides)
Worst pathogen in terms of economic losses?
Powdery mildews
(nickel & dime, highest yield losses)
Bordeaux mixture:
Who discovered it?
What was the crop/country where it was discovered?
Where did the new disease originate that caused it’s discovery?
botany professor Pierre-Marie-Alexis Millardet discovered.
Discovered in Bordeaux, France on grapes.
Originated in America.
control for powdery mildew?
Young tissue generally most susceptible
(common—referred to as “adult plant
resistance”)—PROTECT EARLY

Fungicides/sulfur applications
Cultural; control humidity (in greenhouses)
How does powdery mildew affect plants?
The lower leaves are the most affected, but can spread up and down plant.
Can stunt plant or reduce kernel size.
hypersensitive flex reaction
a defense necrosis, (like tyloses) surrounds pathogen with dead cells to prevent spread of disease
are powdery mildews obligate or non-obligate parasites?
obligate, races differ by host species
(use haustoria)
What is the gene for gene hypothesis?
for every resistance gene, a gene for virulence exists
When do you see oak wilt and powdery mildew symptoms?
late summer/fall
When do you see DED symptoms?
early summer
what are the optimal climate conditions for powdery mildews?
high humidyity and warmth, but NOT free moisture
Of the ascomycete tree diseases, which are homothallic and which are heterothallic? (Oaks, chestnuts, elms)
Hetero: dutch elm disease and oak wilt

homo: chestnut blight
which deuteromycete from lab is a local tomato disease?
Septoria (leaf spot)
septoria also affects wheat (video-septoria leaf blotch)
Which contaminant from lab can cause liver cancer?
Aspergillus flavus (pom pom)
Which are the most important pathogens involved in "damping off"? Give brief description of appearance under scope.
Rhizoctonia (characterized by right angle branching, with constriction at base of branch)
Pythium (with aseptate hyphae)
what is damping off?
killing of seedling before or just after germination
name of the homothallic ascomycte model organism for genetic studies?
epidemiology in plant pathology is...?
the study of plant
What do plant epidemiologists evaluate?
what is disease incidence in the field of plant epidemiology?
• The number or percentage of plants infected
( Often no correlation between disease incidence and
either disease severity or yield loss)
what is disease severity in the field of plant epidemiology?
Percentage of the total plant tissue area infected
define yield loss in plant epidemiology.
Amount of crop not harvested directly attributable to
the disease, i.e. the difference between attainable yield
and actual yield
The amount of disease where control costs just equal
incremental crop returns is called...?
– “economic threshold”
– extremely variable and depends on crop, pesticide, and other costs
What disease causes cankers in plum and cherry?
black knot
The SHAPE of a disease progress curve gives clues to the type of disease you are dealing with...
What kind of disease has an s-shaped "sigmoidal" curve and how are these diseases controlled?
Polyetic/polycyclic diseases

Control is geared toward reducing or delaying the total number of infection cycles or initial primary inoculum and the rate of infection, (moving the "s" to the right, can't complete life cycle)
The SHAPE of a disease progress curve gives clues to the type of disease you are dealing with...
What kind of disease has an "saturation type" sloping off curve and how are these diseases controlled
Monocyclic Diseases; No Repeating Stage

*Control these diseases by controlling the initial inoculum since initial inoculum is proportional to the final amount of disease
What is the range for disease rates (amount of disease increase per unit of time)?
from r = 0.5 per day ( i.e. disease increased
50% per day) for some virulent polycyclics, to…
• 0.02 per year for some polyetics
The calculated area underneath a disease progress curve represents....?
Total amount of disease
AUDPC means?
Area Under the Disease Progress
• Used to compare epidemics
What are Epidemic “rates”, how are they calculated and how and what is their application?
-Rate = “r” = the amount of disease increase
per unit of time
-They are calculated from disease progress curves
-Allows scientists to compare relative virulence and resistance and create predictive models!!
what are the names for the predictive model programs for late blight and apple scab?
"apple scab" and "blightcast"
Describe how predictive models help predict conditions for Stewarts Wilt.
Erwinia stewartii overwinters inside the
bodies of its vector, the corn flea beetle
Flea beetles are killed by prolonged cold
Initial inoculum can be estimated by taking the sum of the mean temperatures for Dec., Jan., and Feb.
When the sum is <-1°C, most vectors are killed and there is little disease
What is a symptom of Fusarium head blight?
white tops of wheat, bleached after ascospores penetrate anthers and proliferate downward through the rachis
What is a sporodochium?
a small, compact stroma that bears the conidiophores (which bear conidia)
*Fusarium head blight is characterized by these.
a thick-walled asexual spore which survives in unfavorable conditions
*Characteristic of Fusarium head blight
How big are prokaryotes?
How many species estimated?
1–5 microns; about
25,000 “species”
important characteristics of prokaryotes?
no organelles
rapid growth rates
reproduce by binary fission
single “chromosome” (nucleoid)
often contain plasmids
what are plasmids?
• extrachromosomal pieces of DNA
Plant pathogenic bacteria: can they grow easily on artificial media? How do they obtain nutrients?
most plant pathogenic bacteria are
“saprophytes” and can be grown on
artificial media
How do bacteria get around?

many are motile by means of flagella,
although this is not significant for longdistance spread
What are the 2 main groups that plant path bacteria are broken down into?
Gram positives which stain purple (P&P)
(the gram stain that differentiates based on cell
wall differences)
Gram negatives that stain red (red light)
2 types of flagella?
• flagella can be polar (located on one end)
• or, peritrichous (all around the cell)
Provide a description of the following bacteria shapes:
cocci = spherical
bacilli = rod-shaped
spirilli = coiled or spiral shaped
pleomorphic = variable; often “comma” or
“y” shape
entry points for bacteria to passively infect a plant.?
hydathodes (tips of leaves; guttation)
lenticels on bark and stems
nectaries on blossom
How are plant path bacteria spread?
Rainsplash the most common shortdistance mechanism
contaminated seed or plant debris
soil inveders vs. soil inhabitants
Most bacteria are “soil invaders”; they can live in the soil or “rhizosphere”
for relatively short periods of time
Many plant pathogenic bacteria are “soil inhabitants”; grow and increase their populations in soil
“forma specialis" for bacteria?
a sub-species designation that permits us to differentiate isolates that are identical in every respect except VIRULENCE PATTERN
Symptoms caused by
Virtually all…
leaf spots
vascular wilts
soft rots
scabs, blights, et
signs of bacterial infection in plant?
very few; bacterial ooze, bacterial streaming
bacteria that form galls?
Agrobacterium s
the major “soft-rotters"
Erwinia sp.
(Memory: somebody named Erwin is soft)
which "bacteria" produce the earthy smell of soil?
Streptomyces sp
Bacteria genus that is often very slow growing, pleomorphic bacteria.
example from Genus:bacterial ring rot of potato
Clavibacter sp

(memory: pleomorphic can be in the shape of a clavicle, clavicles are slow growing)
Bacteria Genus that is broken down into two sub groups based on fluorescence on “King’s B” growth media; fluorescent and non-fluorescence.
Often human pathogens too.
Pseudomonas sp
(memory: falsely(pseudo) singular (mon), because under king b's media, we see there are actually 2 sub groups!!)
Bacteria Genus AKA the "fastidious vascular bacteria" or RLO’s (Rickettsia-like organism)
Xylella sp
What are
bacterial relatives
formerly the “mycoplasma-like organisms”
= MLO’s
smallest known living cells; no cell wall
obligate parasites; increase in Vinca
restricted to sieve cells of plants
usually have a leafhopper vector in which they can multiply
Witches’ brooms a common symptom
What are spiroplasmas?
Spiroplasmas are like phytos but are
helical and can be grown in culture to
produce characteristic “fried-egg” like
citrus stubborn and corn stunt are the only
two major diseases know
All plant pathogenic nematodes are ______ _______ and have a ____mouthpart.
obligate parasites
soybean cyst scientific name?
Heterodera glycines

(introduced pest)
a nematode that is one of the top 5 plant pathogens and a huge problem in warmer climates?
Root knot nematode;
Mebidogyne sp.
significance of Arthrobotrys conoides?
a biological control for nematode pests
fungal rings "lasso" nematodes and kills 'em.
nematode sampling for migratory vs sedentary parasites?
migratory: pie pan filtering
sedentary: flotation method
occuring for more than 1 year
like perennial
When does septoria leaf blotch result in significant yield loss?
when the infection reaches the top three leaves of the wheat plant. (starts on bottom leaves)