Lecture 10a: Plant-Pathogenic Fungi and OOmycetes

Question 1

Late blight of potatoes is caused by

Answer 1

Phytophthora infestants (Irish 1845-1852)

Question 2

Brown leaf spot disease of rice

Answer 2

Bipolaris oryzae

Question 3

Parasite

Answer 3

An organism that gains all/parts of its nutrition requirements from the living tissue of another organism. Doesn’t always cause disease

Question 4

Pathogen

Answer 4

Organism which causes disease

Question 5

Necrotrophs

Answer 5

Kill host tissue feeds off the dead tissue
Botrytis cinerea

Question 6

Biotrophs

Answer 6

Feed on living tissue, often by producing special nutrient-absorbing structures which tap into host tissues
Cladosporium fulvum

Question 7

Hemi-biotroph

Answer 7

initially grow as biotroph, but then switch to necrotrophy and kill the host tissue
Cercospora zeina

Question 8

Broad host range

Answer 8

Usually attack immature or senescing tissue, or plants which are compromised due to environmental factors

Question 9

Narrow host range

Answer 9

The host-specialised pathogen, adapted to overcome the specific defence mechanism of its host

Question 10

Plant pathogenic fungi

Answer 10

• Botrytis cinerea- Necro- Broad- Gray mould
• Cercospora zeina- Hemi bio- Narro- grey leaf spot of maize
• Cladosporium fulvum- biotroph- narrow- Leaf mold of tomato

Question 11

Diagnosing fungal plant diseases

Answer 11

• Symptoms
• Morphological identification
• Molecular identification

Question 12

Genetic identification of fungal plant diseases

Answer 12

• DNA barcoding of fungi using the ITS region
• BLAST search against International Sequencing Database (INSD)
• Species-specific diagnostic assay

Question 13

Internal Transcribed Spacer region

Answer 13

• Fast evolving portion of the ribosomal RNA cistron
• ENables species level identification
• Official barcode for fungi

Question 14

Koch’s postulates

Answer 14

1. Suspected pathogen must be consistently associated with the diseased plants
2. Suspected pathogen must be isolated in pure culture and its characteristics noted
3. The disease must be reproduced in healthy plant inoculated with the isolated pathogen
4. The same pathogen characterised in step 2 must be isolated from the inoculated plant

Question 15

The disease triangle consists of

Answer 15

1. Susceptibility
2. pathogen
3. Favourable environment

Question 16

Disease triangle of grey leaf spot

Answer 16

1. Susceptible maize varieties
2. Cercospora zeina
3. Hot and humid conditions

Question 17

inoculum

Answer 17

Potential infective units of a pathogen

Question 18

Dispersal

Answer 18

Movement of inoculum

Question 19

Infection

Answer 19

Penetration of the host plant by the pathogen

Question 20

Colonization

Answer 20

Establishment of the pathogen in the host plant

Question 21

The disease cycle

Answer 21

Primary inoculum> dispersal> Infection> Colonisation> Symptoms> Production of survival structures> Survival> primary inoculum

Question 22

Avoidance

Answer 22

Use of planting location that is free from the pathogen, selecting a planting time when the pathogen is inactive

Question 23

Exclusion

Answer 23

Utilising disease-free plant material, legal restrictions such as quarantine

Question 24

Eradication

Answer 24

Removal of pathogens from infected tools, soil or seed

Question 25

Protection

Answer 25

Growing resistant plant varieties

Question 26

Managing plant diseases

Answer 26

Avoidance
Exclusion
Eradication
Protection