Mod 4 - Identifying Plant Pests (traditional methods)

Question 1

Diagnosis vs diagnostics

Answer 1

• Diagnostics = the act of actually identifying a pest or pathogen = the answer
• Diagnostics = the science and techniques of making a diagnosis = the method

Question 2

Who might identify a plant pest?

Answer 2

• People in the field e.g. extension officers, farmers etc
• Diagnostician
• Taxonomist

Question 3

Compare an accredited and a certified diagnostic facility.

Answer 3

Accredited = lab competent for all vailidated tests, can do more e.g. for trade, int. purposes.
Certified = can perform specific tests (more limited), program based mainly for national use for survillance.

Question 4

What does validation refer to in diagnostics?

Answer 4

Determining the suitability of a lab method for providing useful anlytical data
- mathematically describes the performance of an assay
- idenetifies potential errors and how likely they are to happen.

Question 5

What do accuracy and proficiency refer to in diagnostics?

Answer 5

• Accuracy = how exact a method or closeness between a measured values and the expected value.
• Proficiency = when a lab demonstrates it can use a method within a specification.

Question 6

What are the methods by which weeds are primarily identified?

Answer 6

• Taxonomic keys
• Written descriptions - websites, literature etc
• comparison with herbarium specimens
• Comparative photos - reliable soruves
• Expert opinion - if other methods don’t work
• molecular methods becoming develope.

Question 7

How are invertebrates identified?

general + molluscs + nematodes

Answer 7

• mainly anatomy based - int/ext
• insects generally = mouthparts, legs, genitailia
• Molluscs = using shell and body shape/colour
• Nematodes = mouthparts, genitalia, body shape and size

Question 8

How are plant pathogens identified?

Generally and for fungi, bacteria and virus

Answer 8

Generally:
- Based on Koch’s postulates - association, siolation, inoculation and re-isolation.

Specifically:
- Fungus = sexual & asexual spores, cultural charcteristics/fruiting bodies.
- bacteria = gram pos/neg, motile or not
- viruses/mollucutes = won’t grow in vitro, based on association and advanced methods e.g. immunological and molecular.

Question 9

How does a dichotomous key work?

Answer 9

• provides readers with 2 contrasting statements at each point
• these are follwoed through until an answer is reached
  Note:
• ## the charcteristic being assessed must be visible

Question 10

What issues arise when using a dichotomus key?

Answer 10

• if you have a specimen that doesn’t fit either choice i.e. new species
• Fungal specimens - if it produces both sexual and aseual spores but only one is present.

Question 11

What are 3 different types of light microscopy?

Answer 11

• Bright field microscopy - simple, most common, specimens are backlit, can stain for contrast.
• dark field microscopy - background is dark, specimen is light, improves contrast without stain.
• Phase contrast - shows organells that can’t be seen in bright field, also better tha BF for translucent specimens.

Question 12

How can non-culturable pathogens be identified?

Answer 12

proof by association
- Pathogenicity testing - bioassays using indicator hosts to show a specific set of symptoms.
- Transmissability - vector transmission assays
- Visual detection - extracted particles examined under microscopes.
- **Serological tests **- immonoassays e.g. ELISAs
- **molecular techniques **- based on DNA or RNA e.g. PCR