-
Phytopathology
study of plant diseases/suffering
-
3 main areas of study in plant pathology
etiology, epidemiology, control/management
-
"Father of Botany"?
- Theophrastus
- wrote Enquiry to Plants and On the Causes of Plants
-
Festival held in ancient Rome to appease the god of rust?
Robigalia
-
Patron Saint of Ergotism?
St. Anthony
-
Women accused as being witches during the Salem witch trials often had what disease?
Ergotism
-
Establisher of "germ theory" and disprover of "spontaneous generation"?
Louis Pasteur
-
Two big historical events involving plant pathology?
Irish Potato Famine (potato late blight) and the Bengal Famine (brown spot of rice)
-
Disease
Any deviation from normal state of the plant from abiotic or biotic factors
-
Injury
Random event, occurs swiftly (can be predisposition for disease)
-
Symptom
A host reaction, an external reaction of plant as a result of disease
-
Sign
Pathogen, part of a pathogen in/on a host
-
Non-infectious diseases
Caused by abiotic factors, non-transmissible
-
Infectious diseases
Caused by biotic factors, transmissible
-
Parasites
Organism that is partially or completely dependent on another organism (host) for its substience, grows and multiplies at expense of host
-
Pathogens
a biological agent responsible for inciting disease
-
Pathogenicity
capacity to insite disease
-
Biotrophs
obligate parasites (grow and reproduce only on living host and difficult or impossible to culture)
-
Necrotrophs
Organisms that cause death of host tissues as they grow through them (can be cultured)
-
Non-obligate parasites
Can live on dead or living host
-
Facultative parasites
Live most of the time on dead organic materials but can sometimes become parasites (weak parasites)
-
Saphrophytes
- Organisms that are able to live on dead materials (can't be on living cells)
- like moulds
-
Facultative Saphrophytes
most of the time are parasites, no living host around then they can continue to live as a saphrophyte for a while (not forever)
-
Lesion
a localized diseased area or wound
-
Pustule
An eruption of the epidermis caused by spores moving to the surface of the tissues
-
The disease triangle
virulent pathogen - susceptible host - favorable environment
-
Other complexities that may accompany the disease triangle?
- vector
- alternate host (to complete cycle)
- complex of pathogens
- human activities
-
The disease pyramid
virulent pathogen - susceptible host - favorable environment - TIME
-
Different systems of classification of plant diseases
- according to symptoms
- according to plant organ affected
- according to type of plant affected
- storage diseases, post-harvest diseases
-
Inoculum
any structure(s) produced by pathogen and involved in infection process (ex. spores, mycelium, etc)
-
Primary (initial) inoculum
inoculum responsible for initiating disease cycle
-
Secondary inoculum
inoculum that originates from infections caused by primary inoculum and responsible for additional infection
-
Sources of inoculum
- plant debris, volunteers, alternative hosts
- also seed, tubers, transplants, cuttings, etc
- outside sources
-
Disease cycle
chain of events involved in disease development; includes all the stages of host infection and pathogen development and reproduction
-
Monocyclic disease
- simple interest diseases
- only one disease cycle per season (no secondary inoculum producted)
- soil borne, systemic
-
Polycyclic disease
- compound interest diseases
- more than one disease cycle per season (both primary and secondary inoculum produced)
- most diseases
-
Etiology
Causes of plant disease
-
Biotic agents
Infectious or transmissible, more gradual
-
Abiotic agents
Non-infectious or non-transmissible, very distinguishable border
-
Examples of abiotic causes of plant disease
- Unfavourable temperature
- Water relations
- Unfavourable soil pH
- Nutrient deficiencies
- Air pollutants
- Herbicides
-
Examples of biotic causes of plant disease
- Fungi + fungal-like organisms
- Viruses and viroids
- Bacteria
- Phytoplasmas
- Nematodes
- Parasitic higher plants
-
Two main groups of fungal-like organisms
- Kingdom Protozoa
- Kingdom Chromista
-
Kingdom: Protozoa
contains many microorganisms and fungal-like organisms
-
Kingdom: Protozoa
Phylum: Myxomycota
Produce a plasmodium or plasmodium-like structure
-
Kingdom: Protozoa
Phylum: Myxomycota
Class: Myxomycetes
- the slime moulds
- body=amorphous plasmodium
-
Amoeboid
slimy mass of cytoplasm with many nuclei
-
Spore
propogative unit carrying out dispersal/survival function, does not contain a pre-formed embryo
-
Syngamy
- union of two gametes to form a zygot
- involves plasmogamy and karyogamy
-
Kingdom: Protozoa
Phylum: Plasmodiophoromycota
Class: ?
Order: Plasmodiophorales
- Endoparasitic slime moulds
- obligate parasites
- plasmodia produced within cells of roots and stems of plants
-
Kingdom: Protozoa
Phylum: ?
Order: Plasmodiophorales
- Produce zoosporangia that give rise to zoospores in early summer
- Plasmodia produce resting spores -> zoospores in following season
-
Hyperplasia
Number of cells increase (like cancer)
-
Hypertrophy
Cell size increases
-
Plasmodiophora brassicae
- Root parasite, cause of clubroot of crucifers
- forms galls on roots
-
Management of clubroot
- well-drained soil
- use healthy transplants
- sanitation
- crop rotation
- resistent cultivars
- fungicides
- bait crops
-
Spongospora subterranea
- cause of powdery scab of potato
- hypertropy
- cosmetic infection
- vector of moptop virus
-
Management of powdery scab of potato
- crop rotations
- disease-free seed
- crop in porous and well-drained soils
- chemical treatments not usually effective
-
Polymyxa graminis
- common parasite of the roots of cereals
- no significant damage to roots
- vector of soilborne wheat mosaic and barley yellow mosaic viruses
-
Kingdom: Chromista
- Unicellular/multicellular, filimentous or colonial organisms
- contain brown algae, diatoms, oomycetes
-
Oomycetes/Phylum: Oomycota
- Produce coenocytic hyphae
- 2 kinds of spores: zoospores and oospores
-
Zoospores
asexual and biflagellate
-
Oospores
- Sexual, produced through two morphologically dissimilar gametes
- Thick walls
-
Oogonium
female cell (multinucleiate)
-
Antheridium
male cell (one nucleus)
-
Plasmogamy
fusion of two mycelia
-
Karyogamy
fusion of two nuclei
-
Kingdom: Chromista
Genus: Pythium
- facultative parasite
- causes dampening-off of seedlings, seed decay, root rots
-
Dampening off
a disease that causes collapse or dent of seedlings before or after emergence
-
Management of Pythium diseases
- Greenhouse -> soil sterilization
- Fungicides at moderate disease pressure
- Good soil drainage
- seeding depth
- seeding time
-
Pythophthora infestans
- potato famine in Ireland (1840s)
- Two mating types, A1 and A2: pathogen variability through sexual recombination
- Re-emerging disease
-
Heterothallism
fungi producing compatible male and female gametes on physiologically distinct mycellia (ex. not self-fertile)
-
Homothallism
Fungi producing compatible male and female gametes on same mycellium (ex. self-fertilizing)
-
Management of late blight of potatoes
- use disease-free seed (certified)
- spray recommended fungicides according to recommended calandar
- use adequate spacing
- store in cold, dry location to prevent progress of infection during storage
-
Albugo candida
causes white rust of crucifers
-
Stagheads
- infection of flower buds and growing tips results in swelling, forming large deformed structures that contain oospores
- happens with white rust of crucifers
-
sporangiophore
- a specialized branch bearing one or more sporangia
- a stalk of sporangium
-
Sorus
a cluster or mass or spores or sporangia
-
Management of white rust
- crop rotation (3yrs)
- resistance
- clean seed
- control volunteers
- often occurs as a complex with downy mildew
-
Peronospora parasitica
- cause of downy mildew of canola and mustard
- when seen on plant you see chlorosis and downy layer of sporangia underneath leaf
-
Plasmopora viticola
- cause of downy mildew on grape
- important in the history of disease control (first fungicide was for this->Bordeaux mixture)
|
|