Pl Sc 380 to midterm 1

study of plant diseases/suffering

etiology, epidemiology, control/management

• Theophrastus 
• wrote Enquiry to Plants and On the Causes of Plants

Robigalia

St. Anthony

Ergotism

Louis Pasteur

Irish Potato Famine (potato late blight) and the Bengal Famine (brown spot of rice)

Any deviation from normal state of the plant from abiotic or biotic factors

Random event, occurs swiftly (can be predisposition for disease)

A host reaction, an external reaction of plant as a result of disease

Pathogen, part of a pathogen in/on a host

Caused by abiotic factors, non-transmissible

Caused by biotic factors, transmissible

Organism that is partially or completely dependent on another organism (host) for its substience, grows and multiplies at expense of host

a biological agent responsible for inciting disease

capacity to insite disease

obligate parasites (grow and reproduce only on living host and difficult or impossible to culture)

Organisms that cause death of host tissues as they grow through them (can be cultured)

Can live on dead or living host

Live most of the time on dead organic materials but can sometimes become parasites (weak parasites)

• Organisms that are able to live on dead materials (can't be on living cells) 
• like moulds

most of the time are parasites, no living host around then they can continue to live as a saphrophyte for a while (not forever)

a localized diseased area or wound

An eruption of the epidermis caused by spores moving to the surface of the tissues

virulent pathogen - susceptible host - favorable environment

• vector
• alternate host (to complete cycle)
• complex of pathogens
• human activities

virulent pathogen - susceptible host - favorable environment - TIME

• according to symptoms
• according to plant organ affected
• according to type of plant affected
• storage diseases, post-harvest diseases

any structure(s) produced by pathogen and involved in infection process (ex. spores, mycelium, etc)

inoculum responsible for initiating disease cycle

inoculum that originates from infections caused by primary inoculum and responsible for additional infection

• plant debris, volunteers, alternative hosts
• also seed, tubers, transplants, cuttings, etc
• outside sources

chain of events involved in disease development; includes all the stages of host infection and pathogen development and reproduction

• simple interest diseases
• only one disease cycle per season (no secondary inoculum producted)
• soil borne, systemic

• compound interest diseases
• more than one disease cycle per season (both primary and secondary inoculum produced)
• most diseases

Causes of plant disease

Infectious or transmissible, more gradual

Non-infectious or non-transmissible, very distinguishable border

• Unfavourable temperature
• Water relations
• Unfavourable soil pH
• Nutrient deficiencies
• Air pollutants
• Herbicides

• Fungi + fungal-like organisms
• Viruses and viroids
• Bacteria
• Phytoplasmas
• Nematodes
• Parasitic higher plants

• Kingdom Protozoa
• Kingdom Chromista

contains many microorganisms and fungal-like organisms

Produce a plasmodium or plasmodium-like structure

• the slime moulds 
• body=amorphous plasmodium

slimy mass of cytoplasm with many nuclei

propogative unit carrying out dispersal/survival function, does not contain a pre-formed embryo

• union of two gametes to form a zygot
• involves plasmogamy and karyogamy

• Endoparasitic slime moulds
• obligate parasites
• plasmodia produced within cells of roots and stems of plants

• Produce zoosporangia that give rise to zoospores in early summer
• Plasmodia produce resting spores -> zoospores in following season

Number of cells increase (like cancer)

Cell size increases

• Root parasite, cause of clubroot of crucifers
• forms galls on roots

• well-drained soil
• use healthy transplants
• sanitation
• crop rotation
• resistent cultivars
• fungicides
• bait crops

• cause of powdery scab of potato
• hypertropy 
• cosmetic infection
• vector of moptop virus

• crop rotations
• disease-free seed
• crop in porous and well-drained soils
• chemical treatments not usually effective

• common parasite of the roots of cereals
• no significant damage to roots
• vector of soilborne wheat mosaic and barley yellow mosaic viruses

• Unicellular/multicellular, filimentous or colonial organisms
• contain brown algae, diatoms, oomycetes

• Produce coenocytic hyphae
• 2 kinds of spores: zoospores and oospores

asexual and biflagellate

• Sexual, produced through two morphologically dissimilar gametes
• Thick walls

female cell (multinucleiate)

male cell (one nucleus)

fusion of two mycelia

fusion of two nuclei

• facultative parasite
• causes dampening-off of seedlings, seed decay, root rots

a disease that causes collapse or dent of seedlings before or after emergence

• Greenhouse -> soil sterilization
• Fungicides at moderate disease pressure
• Good soil drainage
• seeding depth
• seeding time

• potato famine in Ireland (1840s)
• Two mating types, A1 and A2: pathogen variability through sexual recombination
• Re-emerging disease

fungi producing compatible male and female gametes on physiologically distinct mycellia (ex. not self-fertile)

Fungi producing compatible male and female gametes on same mycellium (ex. self-fertilizing)

• 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

causes white rust of crucifers

• infection of flower buds and growing tips results in swelling, forming large deformed structures that contain oospores
• happens with white rust of crucifers

• a specialized branch bearing one or more sporangia 
• a stalk of sporangium

a cluster or mass or spores or sporangia

• crop rotation (3yrs)
• resistance
• clean seed
• control volunteers
• often occurs as a complex with downy mildew

• cause of downy mildew of canola and mustard
• when seen on plant you see chlorosis and downy layer of sporangia underneath leaf

• cause of downy mildew on grape
• important in the history of disease control (first fungicide was for this->Bordeaux mixture)