W3, Biology and diagnosis of plant pathogens Flashcards
What’s the plant?
What’s the disease?
Soft rot in apple
What’s the plant?
What’s the disease?
Black spot on field pea
What’s the plant?
What’s the disease?
Grapevine leaf roll
What’s the plant?
What’s the disease?
Downy mildew on grapevine
What’s the plant?
What’s the disease?
Powdery mildew on cucumber
What’s the disease?
Mosaic virus
What’s the disease?
Damping off (post emergence)
What’s the plant?
What’s the disease?
Powdery mildew on grapevine
What’s the plant?
What’s the disease?
How can you tell it apart from other diseases that it resembles?
Shot hole in almond
→ Red discolouration that looks like rust pustules, but don’t rub off.
→ Holes eventually form in the leaf once the discoloured areas fall out
What’s the disease (of the plant on the right)?
Phytophthera root rot
What’s the genus?
What’s the disease?
Rust on Prunus
What type of plant is this and what disease does it have?
Shot hole disease in stone fruit
What’s the plant?
What’s the disease?
What other symptoms occur that aren’t visible in the image?
How can you tell it apart from other diseases that it resembles?
Almond rust (aka prune rust)
→ Red/orange dots on the underside of the leaf
→ If the pustules rub off, its rust. If they don’t it’s probably the early stages of shot hole disease.
What’s the disease?
Damping off (pre-emergence)
What’s the plant?
What’s the disease?
Witches broom of willow
What’s the disease?
What’s the plant?
Antracnose (black spot) on grapevine
What’s the plant?
What’s the disease?
Phytophthera root rot of banksia
What’s the plant?
What’s the disease?
Sugarcane smut
What’s the plant?
What’s the disease?
Shot hole in almond
What is an easy method for distinguishing rust from other similar-looking diseases?
Rub the pustules on the under-side of the leaf - if they come off it’s rust.
What’s the plant?
What’s the disease?
How can you tell it apart from other diseases that it resembles?
Almond rust (aka prune rust)
→ If the pustules rub off, its rust. If they don’t it’s probably the early stages of shot hole disease.
What’s the difference between signs and symptoms?
Sign: Visible pathogen structures
Symptoms: Plant response to the pathogen
What’s the plant?
What’s the disease?
Botrytis bunch rot (on grapes)
What are the steps for identifying a plant pathogen?
- Identify the host species
- Perform preliminary examination of the host and/or specimen
- Prepare a list of possible causes
- Collect background information (soil condition, management history, local pest/disease outbreaks, etc.)
- Perform thorough visual examination of the specimen and record observation
- Perform low-power examination (hand lens or dissecting microscope), looking at/for:
- Fungal
- hyphae
- reproductive structures (conidia/ophores, sporangia/ophores)
- growth habit
- Nematodes
- Colour
- Size
- Any other diagnostic features
- Perform high power examination (compound microscope); look for the same things previously stated.
- Perform advanced tests
- Fungi:
- moist incubation to encourage sporulation
- culture (view under low- and high-powered microscopes)
- septa
- reproductive structures (conidia/ophores, sporangia/ophores)
- size, shape, and colour of spores
- the presence of rhizoids
- perform metabolic analysis
- Bacteria
- Culture (view under compound microscope)
- Morphology (shape, size, elevation, etc)
- Biochemistry
- Gram stain
- Infect a healthy host to confirm symptoms are a result of the pathogen
- Depends on the value of the crop/pathogen.
If no pathogen was found, the problem is environmental/nutritional/etc
When a pathogen is identified, research and prepare recommendations for management
At each stage of the process, attempt to identify the pathogen by comparing the diagnostic features observed with diagnostic information in relevant reference material.
What’s the plant?
What’s the disease?
Rust on grapevine
What’s the plant?
What’s the disease?
Botrytis bunch rot (grey mould) on grapes
What’s the fruit?
What’s the disease?
Plum pox
What’s the plant?
What’s the disease?
Rust on roses
What’s the plant?
What’s the disease?
Utypa dieback of apricot
What’s the plant?
What’s the disease?
Leaf curl on peach
What’s the plant?
What’s the disease?
Common scab on potato
What’s the plant?
What’s the disease?
Bacterial canker in cherry
What’s the (type of) plant?
What’s the disease?
Powdery mildew on a cereal
What’s the plant?
What’s the disease?
Utypa dieback on apricot
What’s the plant?
What’s the disease?
How can you tell it apart from other diseases that it resembles?
Shot hole in almond
→ Red discolouration that looks like rust pustules, but don’t rub off.
→ Holes eventually form in the leaf once the discoloured areas fall out
What’s the disease?
What’s the plant?
Apple scab
When would you want to scout a grapevine your Utypa dieback?
- Spring
- You want to be able to see the shoots easily and evaluate them at a relatively young stage so as not to have healthy shoots overtake/hide diseased ones from sight.
What’s the plant?
What’s the disease?
Collar rot on grape
What’s the plant?
What’s the disease?
Potato wart disease
What’s the plant?
What’s the disease?
Soft rot of potato
What’s the plant?
What’s the disease?
Bacterial wilt of tomato
What’s the plant?
What’s the disease?
Loose smut on wheat
What’s the plant?
What’s the disease?
Bacterial dieback of pistachio
What’s the plant?
What’s the disease?
Utypa dieback of grapevine
What’s the plant?
What’s the disease?
Collar rot on chestnut seedling
What’s the plant?
What’s the disease?
How can you tell it apart from other diseases that it resembles?
Shot hole in almond
→ Red discolouration that looks like rust pustules, but don’t rub off.
→ Holes eventually form in the leaf once the discoloured areas fall out
What’s the plant?
What’s the disease?
Scab on citrus
What’s the plant?
What’s the disease?
Stem rust on a cereal
What is the plant?
What is the disease?
What are some common symptoms other than what the image shows?
Powdery mildew on grape leaves
→ Under the scope you’ll see yellow fruiting bodies
→ Don’t always see grey mould
→ Can start out as patchy chlorosis
What’s the plant?
What’s the disease?
Fig mosaic virus
What’s the fruit?
What’s the disease?
Powdery mildew on grapes
What’s the plant?
What’s the disease?
Leafroll of grapevine
What’s the plant?
What’s the disease?
Club root on brassica
What’s the plant?
What’s the disease?
Botrytis grey mould on tomatoes
What’s the plant?
What’s the disease?
What other symptoms occur that aren’t visible in the image?
How can you tell it apart from other diseases that it resembles?
Almond rust (aka prune rust)
→ Chlorotic dots on the surface of the leaf
→ If the pustules rub off, its rust. If they don’t it’s probably the early stages of shot hole disease.
What’s the plant?
What’s the disease?
Bacterial canker in cherry
What’s the plant?
What’s the disease?
Bacterial canker in cherry
What’s the plant?
What’s the disease?
Crown gall on rose
What’s the plant?
What’s the disease?
Crown gall on grapevine
What’s the plant?
What’s the disease?
Eutypa dieback of grapevine
What are two symptoms of almond rust?
→ Chlorosis on the upper-surface of the leaf
→ Orange/brown pustules on the under-side of the leaf that come off when rubbed.
What are some common symptoms of:
Rust
Chlorosis on upper leaf surface
Small lesions on leaves and stems, usually rust-coloured, often surrounded by chlorotic halo.
What are some common symptoms of:
Blight
General, rapid browning and death of affected organs (leaves, flowers, branches)
What are some common symptoms of:
Shot hole disease
Starts out as small chlorotic dots with a red/purpley ring around the outside.
The middle dies (becomes necrotic) and falls out, leaving a hole.
What are some common symptoms of:
Canker
Localised necrotic lesion on stem or fleshy organ, often sunken.
Can just look like a black area.
What are some common symptoms of:
Eutypa dieback
Similar to canker
Gummy, sappy ooze being exuded
Dieback of limb(s).
What are some common symptoms of:
Eutypa dieback
Similar to canker
Gummy, sappy ooze being exuded
Dieback of limb(s).
What is a quick method for checking if a disease is caused by bacteria?
Placing stem/root segments in a tube of water and observing for turbidity (which indicates bacterial infection).
Or, in a lab, you could place tissue from the margin of a lesion in water on a slide, and observe microscopically for bacteria streaming from the cut surface.
What source of disease (virus, bacteria, or fungi) would you expect from these symptoms:
mosaic, mottling, rolling, dwarfing
Virus.
What source of disease (virus, bacteria, or fungi) would you expect from these symptoms:
oily leaf spots, blight, ooze
Bacteria.
What source of disease (virus, bacteria, or fungi) would you expect from these symptoms:
spores, spore-bearing structures
Fungi.
