Postharvest pathology Flashcards
How are fungi dispersed? How do they germinate?
spores
germinate in favorable conditions (moisture, temp, nutrients, O2) -> form germ tube
Spores may be in ____ form or ____ form; it is the ____ form that spreads disease
sexual, vegetative
vegetative (multiplies)
Describe the process of spore germination:
absorb moisture
swell: increased O2 consumption, CO2 evolution, synth DNA, RNA, protein
germ tube protrudes, lengthens, forms side branches
How does the fungi penetrate the tissue of the fruit?
produce CUTINASE -> hydrolyze cutin
penetation of infection peg
How does tissue invasion and rotting occur?
fungi penetrate, branch and invade flesh (spread mycelium)
secrete toxins, enzymes that digest
What are resistance mechanisms to infection?
fruit skin (cuticle, epidermis) wound healing (create lignin like substance, like scab) phenolic compounds (toxic to fungi) inhibitors (post infection inhibitors, PHYTOALEXIN)
Sources of pathogens:
before harvest
The typical growth pattern of microorganisms:
sigmoid curve
lag phase, exponential phase, diminishing growth phase, stationary phase
To extend shelf life of fruit and veg, the ____ phase should be extended, and ____ phase should be slowed
lag; exponential
The most important control of microbial growth:
refrigeration
True/False: fungi cannot grow in refrigeration
False; some can grow at subzero temperatures; must freeze fruit
the purposes of refrigeration in preventing microbe spoilage:
- lower temp below minimum growth temperature
- lower before lag phase completion
- kill spores of cold-sensitive fungi while germinating
___ is toxic when inhaled by humans, but can still be useful for its anti____ properties
CO
antifungal
How does modified atmosphere affect fruit and veg disease susceptibility?
direct: less O2 suppresses growth
indirect: increases disease resistance of fruit/veg
O2 concentration below ____ is necessary for a beneficial effect of suppressing microbial growth
1% (use hypobaric storage)
