Lecture 14 Week 10 - Postharvest Diseases

Question 1

What is the ecological function of a fruit?

Answer 1

Seed dispersal

Question 2

How much produce is lost to spoilage?

Answer 2

About 1⁄4

Question 3

What are 5 causes of postharvest disease?

Answer 3

• Genetic susceptibility: relationship between host & pathogen
• Maturity and ripeness: most pathogens when most ripe
• Temperature and moisture
• Handling: mechanical damage attracts pathogens
• Storage: needs to be cooled

Question 4

What pathogens are responsible for postharvest disease?

Answer 4

• Mostly fungi
• Bacteria
  e. g. may exist as endophytes (inside the fruit/plant) or spores

Question 5

What does VBNC mean?

Answer 5

Refers to bacteria that are in a state of very low metabolic activity and do not divide, but are alive and have the ability to become culturable once resuscitated.

Question 6

What are 5 types of resistant bacteria and what are they resistant to?

Answer 6

• Xerotolerant: dry conditions
• Psychrotolerant: cold
• Thermotolerant: heat
• Tolerant of low pH
• Tolerant of low O2 availability

Question 7

What are 8 strategies to prevent postharvest disease?

Answer 7

1. Field hygiene & sanitation
2. Hold water dips (stops fungus growing)
3. Fungicides & inhibitors e.g. sulphur pads
4. Refrigeration (psyocrotrophic bacteria may survive)
5. Drying with sugar & salt (can damage produce though)
6. Gamma irradiation
7. Filtration e.g. air
8. Controlled atmosphere e.g. decreasing O2

Question 8

Difference between dormancy, latency & quiescence? Does this pose a risk to biosecurity?

Answer 8

D: the propagules do not germinate
L: infected but not symptoms evident - waiting for very specific conditions
Q: infected but colonisation temporarily stopped - in a resting phase
Biosecurity risk? Yes.

Question 9

What is a MYCOTOXIN? What are 2 example of a type of mycotoxin?

Answer 9

Any toxic substance produced by a fungus.

e. g. Aflatoxin - Aspergillus flavus (toxic @ 1ppm) - rots corn
e. g. Fumonisins - Fusarium spp

Question 10

What are 4 examples of postharvest diseases?

Answer 10

1. Brown Rot in stonefruit - likes warm wet conditions - managed by sanitation, fungal sprays & careful handling
2. Blue & Green Moulds on citrus - spores get in through ruptured oil glands - washing, fungacide sprays, avoiding damaged fruit
3. C. musae on bananas - airborne spores get into green bananas - quiescent until ripening, stimulated by ethylene
4. Antifungal dienes in avocado peel - don’t germinate until ripening
5. Grey mould (Botrytis cinerea) in strawberries - spores get into necrotic flowers, quiescent until ripening - produces cutinase & lipase to break down fruit - strawberry combats it by producing oxalic acid which lowers the pH to an optimum level for enzymes to come and attack it.