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plant pathogen

2016-12-27 19:08:24   0  举报

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plant pathogens

microbiology

fungus

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compare biotroph with necrotroph

biotroph

obligate

haustoria

penetrate host cell walls

large surface area inside host

invaginate host cell membrane

uptake nutrients

regulate interaction with host (defense system)

remain separated from plant cell cytoplasm

appressorium

flattened hyphal organ

apply turgor pressur grow into host

limited amounts of lytic enzymes

little damage to host

narrow host range

controlled by specific resistance genes

salicylate-dependent defense pathway

nduce hypersensitive cell death in compatible interaction

necrotroph

non-obligate

no haustoria

copious cell wall degrading enzymes

cause host death

physical damage

photosynthesis disrupted

production capacity altered

wide host range

quantitative resistance genes

jasmonate- and ethylene-dependent defense pathways

produce toxins

plant and host

virulence factor

cell wall degrading enzymes

cutinases

non-specific esterases

toxins

regulation target

fast and significant

specificity

host selective

example: HC toxin by cochliobolus

maize northern leaf blot

suppress initiation of host defense response via inhibition of histone deacetylases

host non-selective

general

inhibit transcription in cell organelles

causing peroxidantion of mabrane lipids

example: tentoxin

by fungus: alternaria alternata

cylic tetrapeptide

bind to cloroplast-coupling factor (energy transfer)

cause spots and chlorosis

effector proteins that act mainly intracellularly

secreted by hyphae or haustoria

via secretion system

act on specific plant targets

gene for gene hypothesis

plant R gene

code for receptors

many

pathogen Avr gene

code for effector proteins

toxin

example

HC toxins

Avr

HC toxin reductase

Hm1 gene (R)

disease

examples

magnaporthe grisea - rice blast

appressoria infect aerial tissues

hyphae infect root tissues

invade vascular system and block transport of nutrient and water

symptom

water-soaking

wilting

abnormal coloration

necrotic: localised or general death of cells or disintergration of tissues

blast: death of young buds

blight

sudden or total discoloration

control

principles

exclusion and avoidance

keep pathogen away from plants

e.g. disinfection of plants and seeds

eradication

elimination of pathogen after establishment

e.g. crop rotation, destuction of diseased plants

protection

placing barrier between pathogen and susceptible host parts

methods

crop rotation

rotate planting immune and susceptible crops

limits disease development

no reservoir for infection

husbandry

maintain good plant health

maintain appropriate environment

eradicate alternative hosts

hygiene

remove dead and infected material

care with pruning

treat seed stocks, sterlise soil

chemical control - fungicides

direct treatment

fungicides

specific action sites

resistance

selection pressure

sysemic fungicides

taken up by xylem vessles

systemic action

biological control

antagonistic microorganisms

competitive colonization of non-virulence fungi

mycorrhizal fungi can limit subsequent infection

plant derived chemicals

induction of host resistance

salicylic acid spray

plant associated bacteria

characteristics for most

soft tissue

sub tropical

rode shaped - bacilli

specific pathogenicity factors

saprophytic

examples

burkholderia

xanthomonas

pseudomonas

erwinia

plant associated fungi

most

saprotrophically

majority of phytopathogenic fungi belongs to ascomycetes and basidiomycetes

woody plants vulnerable

enzyme that breakdown cellulose and lignin

vegetative fungi body is mycelium

made up of thread like hyphae

disperse by spores (sex/asex)

most common - conidia/conidiospores

resting stages

chalmydospores / sclerotia

fungal lifestyle

biotroph

feed on live cells

necrotroph

kill before ingestion

hemibiotroph

first bio then necro

obligate parasite

facultative parasite

parasitic or other (saprobe)

plant defense/resistance

gene for gene hypothesis

host R gene

plant Avr gene

defense mechanisms

recognition

PAMP/MAMP, e.g. flagellin, LPS and chitin

R genes for recognition of specific pathogens

direct biding

recognization of modified protein caused by pathogen

resistance

pre-formed barrier

cuticle

thick, multilayer hydrophobic pectic compounds

wax cutin cellulose and hemicellulose pectin

cell wall

nduced barriers

cork layers

tyloses

lignitubers

biochemical resistance (plant immune system)

STR: short term response

innate immunity

reactive oxygen species

response: hypersensitive response: surrounding cells are signaled to apoptosis

SAR: systemic acquired resistance

delayed long-term

communication of damaged tissue with rest of plant

via hormones:

jasmonic acid

ethylene

salicylic acid

lead to global change

protect from further intrusion

produce phytolexins and antimicrobial proteins (defensins)

aromatics, no edibale plants

natural enemies

Phytoalexins

low molecular weight

syn de novo when elicited

may

puncture cell wall

delay maturation

disrupt metabolism

prevent reproduction

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