Exam notes Flashcards
Plant Defense (structural)
pre existing structures
formed in response to pathogen invasion
cellular structures
cork layers
stop phy advance fungi,bac,virus,nematodes
stop nutrients going pathogen
stop toxin movement from pathogen
Abscission layers
middle lamella dissolves and dead area fall out
caused by fungi,bac,vir
shot hole sys
Tyloses
overgrowths of the protoplasts of adj living parenchymatous cells protrude into xylem vessels through pits
biochemical defense
pre existing bioch def
lack of essential factors
induced by attack pathogen
biochem induced by attacking pathogen
hypersensitive response
production of chem
induced antimicrobial chem
*phytoalexins
*fungitoxic phenolics
*phenol-oxidizing compounds
(peroxidase)
*enzymes (PR proteins,chitinase)
*inactivation of path enzyme
*release of fungitoic cyanides
*detoxification path toxins
*systemic acquired resistance
Phytoalexins
very specific chem R induced by elicitor produced by host
tulipalin against Fusarium
fungitoxic phenolics
polyphenoloxidase
peroxidase
phenol-oxidizing compounds
PR proteins
chitinase
enzymes
polygalacturonase inhibitor in orange rind
inactivation of pathogen enzymes
amygdalin in stone fruit
release of fungitoxic cyanides
Chitinase
breaks down cell wall
System acquired resistance
- induced chem or microorganisms
- signal transport through plant
- systemic activated resistance
host defense
resistance varieties are best means of crontrol
- least expensive
- most effective
- environmentally safe
Pathogens have genes encoding virulence factors
often specific for infection of a few plants
pathogenicity factors
necessary for a pathogen to cause disease on a certain species of host plant
virulence factors
necessary for or enhancing the ability of a pathogen to cause disease on a certain cultivar, variety, or ecotype of the host plant
avirulence factors
pathogen components used by the host plant to recognize the pathogen through resistance genes
Risistance genes confer resistance to a ________ of a pathogen
specific race
Virulent races of pathogens occur in response to plant resistance:
*genes already present in small number
*mutation
*recombination genetic material
most common non host plant resistance
immunity
True resistance
controlled genetically
(function differently)
Horizontal plant resistance
nonspecific
quantitative
field
durable
multigene
Vertical plant resistance
specific
qualitative
single gene
Susceptible plants do not become infected from apparent resistance due to
the disease escapes
tolerance to disease
gene that confers resistance in the host and pathogen confers virulence
(gene for gene concept)
*operates in many disease
*plant resistance is dominant
*pathogen virulence is recessive
Pathogen produced enzymes
*cutinases
*pectinases
*cellulases
*hemicellulases
*ligninases
*proteinases,lipases
a non ezymatic metabolite of one organism which is injurious to another
toxin
toxins work by
-increasing the permeability of the cell membrane
-inactivating or inhibiting enzyme activity
-inducing a deficiency of an essential growth factor
Non host specific toxins
-effect a wide range of plants
-non essential for pathogen to cause disease
-must be present for disease to occur
T-toxin
-disrupts mitochondria
-susceptibility to fungus and toxin are inherited maternally in cytoplasmic genes
-virulence and t toxin controlled by same fungal genes
Victorin (HV toxin)
-causes leaky plasma membrane
-toxin production controlled by single fungal gene
-toxin responsible for all disease symptoms
Types of growth regulators in plant disease
-auxins
-gibberellins
-cytokinins
-ethylene
characteristics of growth regulators in plant disease
-work at low concentration
-usually synthesized away from site of action
-promote synthesis of messenger RNA molecules
The effects auxins (indole acetic acid -IAA)
-cell elongation and differentiation
-cell membrane permeability
-general increase in respirationn and promote protein synthesis
Auxins (IAA) is produced by
-plant alone or induced by pathogen stress
-pathogen
-degradation of IAA oxidase
Gibberellins
-speed elongation of dwarf varieties
-promote flowering
-cause stem and root elongation
-help fruit growth
-induce IAA formation
Cytokinins
-necessary for cell growth and differentiation
-too much inhibit senescence
-zeatin
excess cause of ethylene
-chlorosis
-leaf epinasty and abscission
-simulation of adventitious roots
-fruit ripening
-increased permeability of membranes
-induction of plant resistance mech.
fungi causes diseases by
-penetration structures
-enzymes
-growth regulators
how does bacteria cause disease
-enzymes
-tissue degradation
-change membrane permeability
-obstruct water movement
bacteria disease of growth regulators cause
hypertrophic growth
nematodes cause disease by
-enzymes that
altered cell walls (pectinases)
-growth regulators due to IAA production, auxin movement
Viruses use ____ to reproduce and cause disease
host
Phytoplasmas cause disease by using _____
growth regulators
fungal pathogenicity factors
necessary for a pathogen to cause disease on certain species of host plant
fungal virulence factors
necessary for or enhancing the ability of a pathogen to cause disease on a certain cultivar, variety, or ecotype of the host plant
fungal avirulence factors
pathogen components used by the host plant to recognize the pathogen through resistance genes
inoculum
the pathogen or pathogen parts that come in contact with the host, potentially causing disease
propagule
a unit of inoculum, a colony forming unit
fungi inoculum
spores, sclerotia,mycelium
inoculum of nematodes
adults, larvae, eggs
individuals that can be inoculated
-bacteria
-viruses
-viroids
-phytoplasmas
sources of inoculum
-plant debris
-soil
-seed
-transplants (tubers,propagative material)
-weeds (or alternate hosts
how do pathogens (fungi,bacteria,parasitic plants,nematodes) produce inoculum on the plant surface or can reach the plant surface after __________.
tissue break down
viruses, phytoplasmas, and viroids produce inoculum within plants to __________.
help to get out of the plant
inoculum: most inoculum does not reach susceptible hosts and inefficient
wind
inoculum: more efficient way
water
inoculum: insects
efficient form of inoculum
how does direct placement of pathogen into a host
insect vectors
fungi, bacteria, parasitic higher plants must become _____
attached
pathogen to host have ________ and ________
-polysaccharides
-glycoproteins
attachment of pathogen to host by muscilaginous substances associated with ____________
germ tubes
penetration sites for fungi
-moisture
-soil texture
-topography of leaf
penetration sites for bacteria
-moisture
-topography of leaf
penetration sites for nematodes
-tempurature
-soil texture
-plant exudates
-co2
-amino acids
penetration sites for zoospores
plant exudates
the way for invasions in plants
-subcuticular
-surface with haustoria in epidermis
-intracellular or intercellular
-xylem tissue
-intracellular
-intercellular
bacterial invasions start with _____ and then __________
intercellular,
intracellular
definition of infection
process by which pathogens establish contact with susceptible cells or tissues of the host and procure nutrients from them
pathogens grow and/or multiply within the ________ and invade and colonize the plant during infection
plant tissues
symptoms result from infection, usually within _________
a few weeks
delayed symptoms, usually due to poor environmental conditions or wrong host maturity level
latent infection
reproduction:
phytoplasmas move slow and move through _________ and _________ respectively
xylem, phloem
viroids and viruses reproduce in individual cells to high levels and are moved with ____________
phloem
dissemination : spread of pathogen inoculum by ________ or ____ spread
active ; passive
_____,_____, and _____ can be moved in or on seed
fungi, viruses, bacteria
seeds are a _________ form of dissemination
very efficient
the level of infection determines the ability of _________ to transmit the pathogen
the seed
bacteria, nematodes, fungal inoculum in soil can be spread by ————– or ———.
rain; irrigation water
bacteria and some spores are produced in ———- and need rain to wash them down or splash them
sticky matrix
rain can wash ——- or ——- out of the air
spores; bacteria
able to survive indefinitely as saprophytes and usually have many hosts
soil inhabitants
specialized parasites that generally live in close association with their host but my survive in the soil for relatively short periods of time
soil transients
how well fungi survives as a saprophyte in the soil depends on ——– and ——— practices that affect soiil and plant residue
climate ; agricultural
Phytoplasma Identification
-symptoms
-graft transmission
-insect vector transmission
-electron microscopy
-sensitivity to specific antibiotics
-pcr
Virus and Viroid identification
-symptoms
-transmission tests
-serological tests
-electron microscopy
-inclusion body examination
-electrophoresis
-hybridization
-pcr
an organism that lives on or in another organism from which it obtains its nutrition
parasite
the ability of the parasite to interfere with essential functions of the plant and is qualitative
Pathogenicity
degree of pathogenicity of a pathogen and quantitative
virulence
measure of the severity or speed of disease over time in a pathogen population (quantitative)
aggressiveness
plants or plant parts that can be infected by a particular pathogen
host range
organism that obtains its food from dead organic tissue (necrotroph)
Saprophyte
organism that grows and reproduces only on living hosts (biotroph)
obligate parasite
can utilize both living or dead hosts
non-obligate parasite
parasites that usually live on a living host but can survive on dead organic matter
facultative saprophyte
parasites that usually live on dead organic matter, but can attack living tissue
facultative parasite
biotrophic fungi
-cant survive outside of living host
-usually wont grow in vitro
-doesnt usually kill host
-use haustoria to obtain nutrients from the host
-narrow host range
Necrotrophic Fungi
(facultative parasits and facultative saprophytes)
-have wide host ranges
-usually produce toxins or enzymes
-kill plant cells (live saprophytically on dead tissue)
-can survive outside the host
-can often be manipulated genetically
-penetrate through natural openings or wounds
1882 outlined set of procedures to determine the cuase of a disease
Robert Koch
Koch postulates
- The symptoms as well as the signs of the pathogen in the diseased
host are carefully described. - The suspected pathogen is isolated from the diseased host, grown
in pure culture, and described or identified. - A healthy host of the same variety and species is inoculated with the
suspected pathogen. It is later observed for symptoms which must
be identical to those initially described. - The pathogen in re-isolated from the inoculated host and must be
identical to the organism previously isolated.
How do pathogens cause disease?
- -by diverting resources from plant
- -blocking transport of food, minerals and water through plant
- -killing plant
- -direct withdrawal of cell contents
Definition of plant disease
Agrios defines it as “the series of invisible and visible responses of
plant cells and tissues to a pathogenic microorganism or
environmental factor that results in adverse changes in the form,
function, or integrity of the plant and may lead to partial impairment
or death of the plant or its parts.
* Disease is an abnormal physiological process that harms the host.
disease pyramid
(top) conductive environment
(left) susceptible host
(right) virulent pathogen
process by which pathogens establish contact with susceptible host and obtain nutrient from host
infection
the visible presence of the pathogen ex: white fuzz
signs
cannot be cultured, requires a living host
biotrophic fungi
the degree of pathogenicity of a pathogen
virulence
kills host cells through toxins and enzymes and feeds on dead host tissue
necrotrophic fungi
the expression of the pathogen (wilting and yellowing)
symptoms
Enzymeit activities
-cutinase
-chitin deacetylase
-proteases
-acidic cellulases
-pectin methylesterases
-neutral cellulases
-polygalocturonate lyase
-amino acid permease
susceptible plants do not become infected
(disease escape)
(tolerance to disease)
Apparent resistance
For each gene that confers risistance in the host there is a corresponding gene in the pathogen that confers virulence to pathogen
Gene for gene concept
operates in many diseases plant resistance is dominant
pathogen virulence is recessive
Gene for gene concept
to know what is causing the problem before attempting control
Diagnosis
Types of disease control
-plant resistance
-regulation (quarantine and inspection)
-cultural control
-biological control
-chemical control
-reduce initial inoculum
that starts the first disease of the season
Pathogen introduction often causes
epidemics
that starts the first disease of the season
reduce initial inoculation
-pull out infected plants
-clean seed or stock
-eradicate wild or alternate hosts
-crop rotation
-sanitation
-change cropping conditions
-soil solarization
Cultural Control
