Phytophthora

Question 1

Phytophthora symptoms

Answer 1

areas of the plant appear rotten and may have lesions (where the pathogen has consumed the cell’s sugars). wilting occurs, root systems die (dieback), and plant death follow (usually quickly and completely, not one branch at a time)

Question 2

Phytophthora Incubation period

Answer 2

depends of susceptibility of plant (affected by age and species). incubation can range from weeks to months. once wilting starts, death follows quickly.

Question 3

Phytophthora mode of transmission

Answer 3

Indirect via swimming soil borne zoospores
Indirect via vehicles such as car tyres and walking boots
Direct contact between infected and susceptible roots
Waterborne: zoospores can be carried by water and swim short distances to susceptible hosts.

Question 4

phytophthora life cycle

Answer 4

entry via root tips; the mycelia threads grow on the surface and then invade the cells to gain nutrients and moisture for growth and reproduction
Replication is on and in root cells; and is usually asexual; a few cells for a filament, filaments form mycelia threads, and a mass of threads develop into a sporangium
Exit from sporangia in the form of zoospores; if conditions are poor, chlamydospores are produced instead (the resilient forms of the organism ); the soil is a reservoir.

Question 5

Method of Invasion

Answer 5

In favourable conditions, chlamydospores germinate and produce mycelia + sporangia
Sporangia ripen + release zoospores
Zoospores infect plant roots by entering root behind root tip

Mycelia grow throughout root, absorbing carbs + nutrients
Destroys structure of root tissue
Sporangia + chlamydospores form on mycelia
Released into surrounding soil
Spreads

Question 6

impact on host

Answer 6

Destroys root system
Prevents plant from absorbing water + nutrients
First signs
Wilting, yellowing of foliage
Foliage dries out, young feeder roots darken
Infected plants usually die from lack of water + nutrients

Question 7

evolutionary adaptations

Answer 7

In extremes of weather, different spores can be produced
Survive for long periods of time
Germinate when conditions become more favourable
Can take on different shapes
Can move through water
Capable of self-fertilisation if necessary

Question 8

Factors Affecting Spread

Answer 8

Spreads quickly in surface + sub-surface water flows
Spreads slower up-slop + on flat ground
Human activity causes most significant, rapid + widespread distribution
Eg. Road construction, earth moving, infested vehicles, stock movement etc.
Warm / moist soil the best