fungal dispersal

Question 1

multi-hyphal structures

Answer 1

• hyphae can act as a means of dispersal
• differentiation from hyphae is relatively limited
• mycelial cords
• rhizomorphs
• sclerotia
• fruit bodies

Question 2

mycelial cords

Answer 2

• aggregated hyphae <5mm in diameter
• white networks you can see in soil (individual hyphae are microscopic)
• can grow much quicker as not limited by a small diameter
• forage for nutrients
• translocation of water and nutrients

Question 3

dry rot fungus, Serpula lacrymans

Answer 3

• mycelial cord forming fungus
• can explore non-nutrient zones quickly e.g. plaster/bricks
• translocation of water to dry wood so fungus can break it downs
• liquid is exuded from tip of the cord

Question 4

rhizomorphs

Answer 4

• advanced mycelial cord
• root-like structures with a meristem and melanised rind
• high growth rate

Question 5

honey fungus

Answer 5

• uses rhizomorphs to locate and attack healthy (often weakened) trees from a dead tree

Question 6

tropical litter trappers

Answer 6

• fungal rhizomorphs in rainforest understory form nets to trap falling leaves before they hit the ground
• requires high humidity and productivity
• used by birds in nests

Question 7

sclerotia

Answer 7

• mycelial survival structure
• resting structures 1mm-1cm in diameter that can overwinter
• thick melanised rind
• Claviceps spp. (ergot alkaloid)
• Sclerotium spp. (germinate in response to host exudates, onions)

Question 8

fungal spores

Answer 8

• usually <10 micrometers
• low inoculum potential, only a few propagate but lots released
• sporulation tends to coincide with leaf fall

Question 9

factors related to fungal sporulation

Answer 9

• type, asexual/sexual
• response to environmental cues, light CO2 etc
• discharge/dispersal, active, passive, assisted
• dormancy/germination

Question 10

exogenous dormancy

Answer 10

• spores don’t germinate immediately but wait for a signal
• germinate in response to external nutrients e.g. the presence of host metabolites

Question 11

endogenous dormancy

Answer 11

• spores self-inhibit germination
  e.g. Neurospora spp.
• post-fire fungi, 20min at 60C needed for germination

Question 12

phototropism

Answer 12

• positive phototropism of fruiting body
• mushroom grows at right angle in order for spores to be projected the most distance

Question 13

Pilobus spp. (dung fungus)

Answer 13

• angles towards light
• spores must be projected onto fresh vegetation because animals don’t feed near their own dung
• melanin coated spore can resist going through gut
• madA mutant doesn’t respond to light

Question 14

Agaricus bisporus, cultivated mushroom

Answer 14

• will fruit in the dark
• only 2 spores per basidium
• process to optimise efficiency for cultivation, hyphal vs mushroom biomass
• low nutrient peat casing on surface of compost forms baby mushrooms (pinning)
• then open doors, reducing CO2 levels, temperature and humidity causing a flush of mushrooms
• process can then be repeated to create continuous flushes of mushrooms (decreased yield each time)

Question 15

passive spore discharge mechanisms

Answer 15

• rely on wind, air currents etc
  e.g. potato blight oomycete, no specialised mechanism, sporangia only formed in wet conditions as depends on wind/rain

Question 16

rain-assisted spore discharge, Bird’s nest fungus

Answer 16

• cyathus, basidiomycete
• grows on dung
• raindrop falls on nest and spores are splashed upwards and outwards
• spore has string and counterbalance that wraps around grass so it can wait for herbivores

Question 17

Sphaerobolus, active spore discharge

Answer 17

• cell shape change projects spore

Question 18

Pilobolus spore cannon, active spore discharge

Answer 18

• caused by turgor pressure
• can project spores >2m at a 45 degree angle
• lots of force generates, >20,000 g

Question 19

basidiospore, active spore discharge

Answer 19

• projects spores 50-100 micrometers to middle of gill space so spores can then be picked up and dispersed by wind
• droplet of water forms on mature spore, Buller’s drop
• droplet increases in diameter until surface tension breaks and droplet spreada
• makes spore jump

Question 20

airborne dispersal

Answer 20

• project spore into moving air
• air moves faster higher up past boundary layer
• spore pigments protect against UV

Question 21

airborne dispersal, sedimentation

Answer 21

• size/shape of spore determines how far it will be blown
• sedimentation rates depend on particle size
• spores with larger diameters fall the fastest in still air
• in moving air large spores travel large distances

Question 22

SARS-COV-2 airborne transmission

Answer 22

• 2m rule disproven due to creation of aerosols from coughing/sneezing
• rapid evaporation of droplets in low (indoor) humidity create small aerosols of viral particles surrounded by solids (mucin/salts, 2-5% of saliva)
• COVID can remain infective in aerosols for >16 hours and can remain in air for longer and be projected further
• dried saliva inhaled
• aerosols are more important in the spread of COVID than fomites

Question 23

dispersal by animal vectors, examples

Answer 23

• bark beetles, dutch elm disease
• pigs, truffles
• flies, stinkhorn (Phallus spp.)
• man, plant pathogens

Question 24

fungal bioluminescence

Answer 24

• possible for attraction of night-flying insects for spore dispersal
• also drop spores from gills as a means of dispersal

Question 25

Lyme disease

Answer 25

• vector borne, tick Ixodes spp.
• Borrelia burgdorferi, bacteria spirochaete
• viral like symptoms, later arthritic/neurological problems
• zoonotic disease
• little/no human spread
• ancient disease
• 2-3year tick life cycle with 3 hosts