Plant Pathology Final Exam

non-living, pathogens cause non-infections, non-transmissible, diseases. When factors such as temperature, moisture, mineral nutrients, air pollutants occur at levels above or below a certain range tolerated by plants. These are factors.

abiotic

living, pathogens cause infections, transmissible, diseases. May also be called “causal agent” because they are agents, these are fungi, viruses, bacteria, etc.

biotic

Plant diseases, the study of the organisms and the environmental factors that cause plant diseases, the study of the mechanisms by which these factors induce diseases in plants, the study of the interactions between the disease-causing agents and the diseased plants (defense mechanisms), the study of methods to prevent or control diseases to minimize crop losses

plant pathology

a visible abnormality, how the plant responds to the pathogen (not normal function), and a plant’s expression that there is a disruption of an abnormality in the plant

symptom

seedling death just prior to (pre-emergence) or just following emergence (post-emergence) from the soil. Necrotic tissue is seem near the soil line, the necrotic tissue is sunken, and plant falls over, but the top remains green for a period of time

damping off

the belief that plant, human and animal diseases just happen spontaneously and were punishments from gods

spontaneous generation

causes for diseases are microscopic fungal spores that infect the plants

germ theory

Irish were dependent on eating potatoes because they sent wheat     over to the British, the British did not believe in the famine. It deepened the rift between Irish and British, the British landlord refused to believe the famine was serious, they still demanded the cereal; crop as payment of rent. Protectionist trade laws against imports of US corn repealed, the British refused America’s food aid. The environmental conditions was cool, moist conditions accelerate the rate of disease development, summer of 1845 started out hot and dry, weather changed 1.5C to 7C degrees below normal, continuous overcast and rain for 6 weeks, and it accelerated pathogens life cycle by nearly 10X. Free water produced oospores

Late Blight of Potato - Phytophthora infestans

Social was consuming infected grain, common among rural poor who used rye for bread, folk cure was to eat white bread instead of rye bread. Environmental conditions was growing a susceptible host (monoculture) and lack of seed or grain sanitation

Ergot of Rye – Claviceps purpurea

Coffee became a popular drink of England (high demand), produced in Ceylon, Java, and Sumatra (environment), and by 1825 the British developed all of Ceylon for coffee plantations (same growing practices). The environmental conditions, coffee grown over 4000,000 acres (monoculture), both pathogen and host were introduced to a new location, no effective control for the fungus, one rust pustulates (a little colony) on a leaf can contain 150,000 spores, and one leaf could have 100s of pustules

Coffee Rust – Hemileia vastatrix

Corn breeders tried to control the cost of labor-intensive steps in hybrid seed corn production by detasseling plants to control undesirable cross pollination. The environment, by creating Texas male-sterile (TMS) cytoplasm, they introduced a weakness ito the plats, plants carrying Texas cytoplasm were very susceptible to infection by the destructive race T of the fungus, seed carrying the Texas cytoplasm was widely planted

Southern Corn Leaf Blight – Cochliobolus heterostrophus

Chestnuts were economically important for wood, food, and natural products (people were dependent), In 1900’s it was important for rot-resistant wood, food for humans and animals, and tannins in the tanning industry. The fungus was introduced in N.Y. along with chestnut carried over Asia. Perhaps every fourth tree in the Appalachian forests was a chestnut, this is a new contact disease

Chestnut Blight – Cryphonectria parasitica

Constriction of the blood vessels caused appendages to feel like they were burning

Holy Fire and St. Anthony’s Fire

is the thing causing a disease, fungi, bacteria, viruses, nematodes, and parasitic plants, any organism that is capable for producing even if the symptoms cannot be felt, pathogens do not need the host to survive

pathogen

when one organism takes its nutrients from another in doing so causes harm
any organism that has a close relationship with its host and is dependent on its host for life functions, it cannot survive on its own

parasitism / parasite

two organisms living together in close association, both benefiting from the interaction

mutualism

two organisms living together where one gets benefits and the other is not affected

commensalism

the ability of the parasite to interfere with one or more essential functions of the plant and thereby to cause a disease

pathogenicity

the degree of pathogenicity

virulence

the ability to cause disease on only a limited number of plant hosts

host specificity

an interaction between a susceptible host and a virulent pathogen that results in disease

compatible interactions

an interaction between a resistant host and an avirulent pathogen where no disease occurs

incompatible interactions

an organism involved in a symbiotic relationship

symbiont

an organism that derives its nutrients from dead organic matter

saprophyte

a parasite that can grow only in association with a living host

obligate parasite

is an organism that can survive either as a parasite or a saprophyte (an organism that consumes dead organic material for food)

non-obligate parasite

an organism that is primarily a saprophyte but can be a parasite under the appropriate conditions

facultative parasite

an organism that is primarily a parasite but can be a saprophyte

Facultative saphrophyte

the ability of a post plant to overcome the effects of the pathogen

disease resistance

the inability of a host plant to resist the effects of a pathogen

susceptibility

the ability of a plant to survive the effects of a pathogen, despite the incidence of disease. Even the most susceptible host can retain some measure of resistance

tolerance

experiments identified phytophthora infestans as the causal agent of late blight of potato, the father of plant pathology

Anton de Bary

word identified the susceptible stage of the disease by finding germinating spores, he also identifies monocultures as a perfect condition for disease epidemics, work on coffee rust was the first demonstration of disease forecasting

Marshall Ward’s

new host introduced to a native host OR a new plant to a native pathogen (CHESTNUT BLIGHT and FIRE BLIGHT)

new encounter disease

Observe and describe the symptoms in detail

isolate and purify the suspected pathogen (difficult because obligate parasites cannot grow in culture)

inoculate healthy plants with the purified pathogen (disease must reproduce the SAME symptoms as step one)

reisolate the pathogen

Koch’s postulates

what is the disease triangle?

Pathogen – the total virulence, abundance, for a specific pathogen species/race.

Host – the total conditions favoring susceptibility, susceptibility/resistance for a specific plant species/cultivar.

Environmental – the total conditions favoring disease.

any part of the pathogen that contacts the plant and initiates infection. Propagule – one unit of inoculum, regardless of a type of pathogen

inoculum

the stage which causes primary infection, causes an original infection at the beginning of the growing season, after dormancy

primary inoculum

having on disease or life cycle per growing season

monocyclic

having several to many disease cycles in a growing season

polycyclic

Incubation period is varying length before symptoms can be observed, depending on different factors: __ (symptomless) infection periods or colonization may proceed inter-cellularly or intra-cellularly or both.

latent period

live within host tissue without causing death

biotrophs

can switch from biotroph to necrotrophy, necrotrophs kill cells and then consume the contents.

hemi-biotrophs

cutinase enzymes break down the waxy lipid layer covering the surface of the leaves and stem

cuticle

pectinases these enzymes kill cells, presumable due to weakening of the cell wall and the eventual bursting of the cell membrane due to internal turgor pressure

pectin

cellulases break down portions of the cell wall and middle lamella

cellulose

linginase, lignin strengthens plants and is hard to degrade

lingin

 toxic only to one or few host species or even cultivars and no toxicity to other species/cultivars that are resistant to this pathogen, victorin of oats

host specific toxins

toxic to a range of plant species some of which are not even hosts for a pathogen producing these toxins

non-host specific toxins

creates these toxins, these are pathogens which have wide host ranges, they produce non-host specific toxins

necrotrophy

have membrane bound nucleus and mitochondria

eukaryotes

(bacteria and mycoplasmas) lack nucleus and some organelles; all are microscopic, and most are unicellular (some form chains), no nuclear membrane, and no mitochondrial DNA or visible endoplasmic reticulum

prokaryotes

have thin peptidoglycan and possess LPS/Outer membrane

gram positive

have thick peptidoglycan and lack LPS/Outer membrane

gram positive

five control measures?

exclusion

eradication

protection

resistance

avoidance or therapy

preventing the entry and establishment of the pathogen into an area where it is not already present

exclusion

complete or partial removal of the pathogen from an area, a reduction of the population density of the pathogen

eradication

establishing a barrier between the host and the pathogen, the barrier is frequently chemical in nature and does not have to be a physical barrier

protection

limiting pathogen development by the genetic constitution of the host, two generally recognized subcategories are Vertical and Horizontal resistance

resistance

alteration of environmental conditions to avoid pathogen activity, also avoiding periods when environmental conditions are optimum for disease development

avoidance

curing a host after infection has occurred or limiting pathogen development after infection by some treatment of the infected host tissues

therapy

genetic variation in bacteria?

mutants, conjugation, bacteriophages

most common, mistakes that occur during replication of the DNA

mutants

exchange of genetic information between bacterial cells, part or all of the chromosome can be directly transferred from one bacterium to another

conjugation

viruses that infect bacteria, can transfer plasmids

bacteriophages

natural openings in plants?

hydathodes

stomata

nectaries

increased number of cells

hyperplasia

increased cell size

hypertrophy

is the tumor inducing plasmid – it is required for virulence (ability to cause disease).

Ti-plasmid

transfer of DNA – it includes the DNA for auxin and cytokinin. Plasmid are secondary DNA some plants have

T-DNA

Eukaryotic, heterotrophic, absorptive organism what develops a rather diffuse, branched, tubular body and reproduces by means of spores.

Primarily decomposers and medicine (penicillin).

fungi

is a thread-like structure, basic unit

hypha

is a collection of hyphae, a vegetative body

mycelium

hyphae have cross walls

septate

has no cross walls

coenocytic

cross-wall divisions within the hyphae

septum

Fungal growth occurs at the tip of the hyphae;

apical elongation

where most of the new cell wall material is deposited in the terminal 1mm of the hypha.

apical dome

is movement towards chemicals gradient (nutrients), one example is in the rhizosphere (sugars); another example is with zoospores because they move up a chemical gradient

chemotropism

also known as “positive autotropism”, is growth towards other members of the same species, like during sexual reproduction

autotropism

growth away from members of the same species, an example is germinating fungal spores

negative autotropism

the growth directed by touch, contact-sensing or thigmotropism is the directional growth response of cells in relation to topographical guidance cues (aka the ridges, veins, and hairs of leaves and stems). Certain fungi align themselves on plant surfaces according to “touch” or contact stimuli. They grow along the veins to find an opening (stomata).

thigmotropism

the haploid, diploid, or dikaryotic state can be maintained by mitotic divisions. During mitosis DNA is replicated and cells are divided, these new cells maintain the genotype of the parental cells

anamorph or imperfect stage

asexual reproduction

zoospores, conidiaspores, sporangiospores, arthospores, chlamydospores

asexual spores

depends on meiosis, meiosis involved recombination between homologous chromosomes and is a key mechanism for increasing species diversity, the primary mechanism for genetic recombination, this increases genetic diversity which is generated by chromosomal recombination

perfect or telemorph stage

sexual stage

ascospores, oospores, zygospores, basidiospores

sexual spores

millions of spores per day, even at a low mutation rate, you can get new genotypes which lead to genetic variation

mutation

a sequence involving heterokaryon formation, diploidization, and tabloidization often resulting in the formation of recombinant nuclei. The parasexual cycle can occur at ANY point or continuously throughout the life cycle

parasexual cycle

multinucleate cell which contains genetically different nuclei within a common cytoplasm

heterokaryon

hyphae is diploid (2N)

hyphae is coenocytic

cell wall or cellulose

zoospores have two flagella

sporangium produce zoospores

chromista

hyphae is diploid

hyphae is septate or coenocytic

cell wall have chitin

zoospore has single, posterior flagellum

sporangium produce sporangiospores

fungi

Have zoospores

Aseptate

Is an obligate parasite or biotroph

Are not mycorrhizal

Unknown sexual spores

Asexual spore is zoospore

Chytridiomycota

Do not have zoospores

Are aseptate 

Are not obligate parasites or biotroph 

Some mycorrhizal

Sexual spore is zygospore

Asexual spore is sporangiospore

Zygomycota

Do not have zoospores

Are septate

Some obligate parasite or biotroph

Some mycorrhizal

Sexual spore is ascospore

Asexual spore is conidia/chlamydospores

Ascomycota

Do not have zoospores

Are septate

Some obligate parasites or biotrophs

Some mycorrhizal

Sexual spore is basidiospore

Asexual spores are pycniospores, aeciospores, urediniospores, teliospores

Basidomycota

“egg-like” mycelium. They are multinucleate, coenocytic (no cross wall) mycelium, diploid oospore in oogonium, and zoospore in zoosporangium. Have glucan and cellulose in their cell walls

Oomycota

Pythium, Phytophthora, Rhitoctonia, Fusarium

cause damping off

will occur between 10-18 degrees C and will have to occur from 0.5-2.0 hours. Multiple zoospores, eight zoospores per each sporangium. Does not germinate directly, rather divides to zoospores

indirect germination

has a germ tube and will initiate germination itself – it will occur between 18-25 degrees C. Single germ tube, penetration is via an appressorium and penetration peg, this occurs for 2 to 2.5 hours at 15-25 degrees C

direct germination

complete resistance to certain races of a pathogen. Usually a single gene resistance.

vertical resistance