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102 Microorganisms as plant pathogens > Lecture 2 > Flashcards

Lecture 2 Flashcards

Aim: - understand the impact and importance of bacterial plant pathogens - disease caused by bacteria (4 examples) - agrobacterium (natures genetic engineer) - Rhizobium (beneficial plant bacteria) - Mollicutes (2 examples)

1
Q

What are the diseases caused by bacteria

A
  1. ) Fire Blight (apples)
  2. ) Crown Gall
  3. ) Citrus Canker
  4. ) PSA V (virulent)
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2
Q

What bacteria causes Fire Blight

A

Erwinia amylovora

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3
Q

What does Erwinia amylovora affect

A

pears and apples

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4
Q

How does Erwinia amylovora affect plants

A

produces enzymes and toxins that cause necrosis (death of tissue or organ) and death of young shoots
- severe cases, death in trees

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5
Q

How is Erwinia amylovora (fire blight) spread

A

Pollinating insects

water splash

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6
Q

What are ideal conditions for fire blight

A

spring
16 C
anywhere under right conditions

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7
Q

true or false; NZ cannot export apples to Australia due to Fire blight (Erwinia amylovora)

A

true

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8
Q

What causes Myrtle Rust (fungus)

A

Puccinia psidii

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9
Q

Where was Puccinia psidii first reported in and when

A

Brazil
1984
guava

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10
Q

true or false; Puccinia psidii have a wide range of hosts including commercial Eucalyptus species in Brazil

A

true

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11
Q

true or false; Puccinia psidii arrived in Australia in 2010 and was not eradicated

A

true

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12
Q

What do the rust spores of Puccinia psidii look like

A

thick brown walls

enabling them to survive UV in the upper atmosphere

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13
Q

Why is possible that NZ will also be invaded by Puccinia psidii in the future

A

due to Westerly winds from Australia

- Puccinia psidii is very small and can travel very quickly

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14
Q

What causes Citrus canker

A

bacteria

Xanthomonas axonopodis pathovar citri

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15
Q

What are the symptoms of Xanthomonas axonopodis pathovar citri (Citrus Canker)

A

Infected trees display

  • raised brown lesions
  • with water soaked margins
  • yellow halo on leaves, fruit and stem
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16
Q

What happens when the lesions caused by citrus canker is wet

A

lesions ooze bacteria that spread short distances by water splash

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17
Q

What distributes Xanthomonas axonopodis pathovar citri

A

Citrus canker:

  • water splashes (short distance)
  • Strong winds and rain (long distance)
  • people (spread the disease by moving infected plants, or fruit)
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18
Q

What are the effects of Citrus canker on yield

A

low vigor
reduced fruit quality
reduced fruit quantity

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19
Q

in 2005 what hurricane spread citrus canker in America

A

hurricane Wilma

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20
Q

What causes Pierce’s disease (bacteria)

A

Xylella fastidiosa

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21
Q

Where is Xylella fastidiosa a major concern

A

USA

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22
Q

how is Pierce’s disease caused (Xylella fastidiosa)

A
  • caused by fastidious bacterium Xylella fastidiosa

- which invades and blocks plants xylem vessels

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23
Q

How is Xylella fastidiosa transmitted

A

sharpshooters (sucking leafhopper insects)

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24
Q

Where are the symptoms of Xylella fastidiosa (Pierce’s disease) seen

A

Leaves
flowers
canes

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25
Q

How does Pierce’s disease affect the leaves

A
  • Chlorotic spots spread as the centre dries out and becomes brittle
  • concentric zones develop
  • leaves fall prematurely
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26
Q

How does Pierce’s disease affect the flowers

A
  • fruit set is reduced

- berries dry up

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27
Q

How does Pierce’s disease affect canes

A
  • wood fails to mature
  • produce ‘green islands’ of tissue
  • bud break is delayed in the following season
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28
Q

Plants affected by Pierce’s disease die in about….

A

1-5 years

29
Q

What kind of plant does Pierce’s disease infect (likely)

A

grapevines

30
Q

true or false; Xylella fastidiosa is present in NZ

A

false; it is not

so it is a bio-security threat

31
Q

What conditions does Xylella fastidiosa like to establish itself

A

hot areas

- less prevalent where it is cold

32
Q

What causes Psa V

A

Pseudomonas synringae p.v actinidiae

- kiwi fruit bacterial canker

33
Q

What conditions are Psa V likely to develop

A
  • Spring
  • Autumn
  • cool temps
  • high humidity
  • rain
  • 10-20 degrees
34
Q

Where was Psa V first discovered and when

A

Japan

1980s

35
Q

What are the primary symptoms of a plant infected by Psa V

A
  • spots with halo

- curling, brown infected buds

36
Q

What are the secondary symptoms of Psa V

A

red/orange exudatem (substance secreted by plant) shoot die back
cane collapse

37
Q

How is Psa V spread

A
  • windborne pollen
  • strong winds
  • heavy rainfalls
  • animals and humans
38
Q

What organisation monitors Psa V in NZ

A

KVH organisation

39
Q

true or false; about 37% kiwi fruit orchards are infected

A

true

40
Q

true or false; 600 ha Hort 16A gold ripped out till April 2012

A

true

41
Q

How is the Psa V controlled

A 
Chemicals 
plant health and healthy stock
no overhead irrigation
inspections
disinfection of pruning and picking equipment
42
Q

What do you call the new cultivated Psa V resistant kiwifruit

A

Gold3

- which can be grafted

43
Q

What is Agrobacterium tumefaciens

A

natural genetic engineer
- causes Crown Gall disease:
woody plants including peach, apples, roses and vines

44
Q

What kind of pathogen is Agrobacterium tumefaciens

A

biotrophic pathogen

- that genetically modifies the host plant

45
Q

Where is Agrobacterium attracted to

A

wounded roots by plant phenolics

46
Q

How does Agrobacterium infect a plant

A
  • attaches to wounded plant cells and transfers T-DNA from Ti plasmid to host nucleus
  • induces the production of tumor like swellings (galls) on roots or base of the stem
47
Q

What are the tumor cells induced by (Agrobacterium infection)

A
  • induced by a gene on the Ti plasmid

- to produce OPINES (amino acid derivatives) used as an energy source by the bacterium

48
Q

What is Rhizobium

A

A beneficial plant bacteria

49
Q

What type of relationship does Rhizobium make with the roots of certain plants (clover, lupin, peas)

A

symbiotic relationship

50
Q

What does Rhizobium produce that benefits the plant

A

produces root nodules in which nitrogen fixation takes place

- this association has benefits on both the plant and the bacterium

51
Q

true or false; Rhizobium is closely related to Agrobacterium

A

true

52
Q

What is the difference between the jobs of Rhizobium and Agrobacterium

A

Rhizobium is beneficial whilst Agrobacterium is a pathogen

53
Q

What are the steps of how a Rhizobium infects the roots of a plant

A

1.) Roots emit chemical signals to attract bacteria

2.) Bacterial signals stimulate root hairs to
elongate & form an infection thread.

  1. ) Bacteria penetrates root cortex; root cells divide; vesicles containing bacteria (bacteroids) bud into cortical cells
  2. ) Cortex and pericycle cells continue to divide and fuse to form the nodule
  3. ) Nodule continues to grow; vascular tissue grows into nodule (allows movement of N (nitrogen) into the plant)
54
Q

What is Nitrogen fixation

A
  • When the nitrogenase enzyme (rhizobium) enables the ‘fixation of nitrogen’ to ammonium compounds
  • ammonium compounds benefit the plant
  • Some NH4+ diffuses into the soil/water and is converted into N- containing organic compounds (by other bacteria and plants)
55
Q

What are mollicutes

A

bacteria without cell walls

56
Q

What are the effects of mollicutes on plants

A
  • stunting
  • yellowing
  • eventual decline & death
  • redding of leaves
57
Q

What caused the cabbage tree decline

A
  • caused by phytoplasma
  • prokaryote without cell wall
  • obligate parasites cannot be cultured
58
Q

How is the cabbage tree disease spread

A

vectors are plant and leaf hoppers(phloem feeders)

59
Q

What causes Coconut lethal yellowing

A

phytoplasma as well

60
Q

Where was coconut lethal yellowing prevalent

A

-first noted in Florida 1955; killed 75% palms over the next 13 years

61
Q

What are the two examples of mollicutes

A
  • cabbage tree disease

- coconut lethal yellowing

62
Q

How does bacteria usually enters its host

A 
natural openings (stomata)
wounds
63
Q

How are bacteria controlled

A
  • copper based pesticides and/or anitbiotics
  • elimination of inoculum sources (eg. seed contamination in annual crops)
  • genetic resistance are the most effective means of control
64
Q

What are the distinguishing factor of Mollicutes

A
  • small in size
  • lack cell walls
  • instead have a triple layered membrane
65
Q

What are a group of Mollicutes

A

Phytoplasma

- plant pathogens associated with insect vectors

66
Q

Who is Ross Beever

A

a mycologist, that identified that phytoplasma was the causal agent of Cabbage Tree Sudden Decline

67
Q

What is an obligate parasite

A

cannot complete its life cycle without a suitable host

68
Q

true or false; Coconut lethal Yellowing has been identified in Florida in 1955 and was responsible for the loss of 75% of the palms in 13 years

A

true

102 Microorganisms as plant pathogens (4 decks)

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