plant pathogen
2016-12-27 19:08:24 0 举报AI智能生成
plant pathogens
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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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