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Year 2 Biology Ellie M > Plant Disease - Bacteria and Fungi > Flashcards

Plant Disease - Bacteria and Fungi Flashcards

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1
Q

What is a plant disease?

A

Any disturbance brought about by a pathogen or environmental factor which interferes with manufacture, translocation or utilisation of food, mineral nutrients and water in such a way that the affected plant changes in appearance and/or yields less than a healthy plant of the same variety

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2
Q

When was the potato late blight and what caused it?

A

1845-47

Phytophthora infestans

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3
Q

What are the losses due to disease?

A 
Loss of plants
Reduction in yield
Reduction in quality
Post-harvest loss
Costs of management
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4
Q

7 different types of pathogens

A
  1. Viruses and viroids
  2. Bacteria, Mollicutes and mycoplasmas
  3. Protists
  4. Protozoa
  5. Fungi
  6. Nematodes
  7. Parasitic plants
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5
Q

What is a pathogen?

A

An organism capable of causing disease

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6
Q

What is virulence?

A

The degree of disease caused on a particular host

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7
Q

What is a pathovar?

A

(pv.)

In bacteria; a subspecies / group of strains that infect a particular host

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8
Q

Forma specialis

A

(f.sp.)

In fungi; a group of races that infect a particular genus or species of plant

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9
Q

What are Koch’s 4 Postulates?

A
  1. The microoorganism must be found in abundance in all organisms suffering from the disease, but it must not be found in healthy organisms
  2. The microorganism must be isolated from a diseased organism and grown in pure culture
  3. The cultured microorganism should cause disease when introduced to a healthy organism
  4. The microorganism must be reisolated from the inoculated, diseased experimental host and be identified as being identical to the original specific causative agent
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10
Q

What did Koch prove?

A

That Anthrax and TB were caused by a bacterial infection

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11
Q

What are the problems with Koch’s postulates?

A
  • Difficult for obligate parasites (restricted to a particular function or mode of life e.g. intracellular pathogens)
  • Complex for viruses/viroids but transmission can show it is not a pathogen
  • Difficult if host physiology/environment matters for the infection to occur
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12
Q

What is “Normal microbial flora”?

A
  • Microbes that can benefit the plant
  • Bacteria, yeasts and filamentous fungi
  • Occupy suitable environmental niches and perhaps reduce pathogen attachment
  • Promoted by secretion of sugars/amino acids
  • Phyloplane (leaf surface) and rhizosphere (roots)
  • Also endophytes/mycorrhiza
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13
Q

Disease: damping off

A

Poor germination - infection of the seed or seedling, especially in waterlogged soil

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14
Q

Causes of damping off

A

Pythium sp.

Rhizoctonia

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15
Q

Disease: wilt

A

Infection of roots or vascular tissue

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16
Q

Causes of wilt

A 
Fusarium/Verticillium sp.
Armillaria mellea (Honey fungus)
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17
Q

Disease: stem base

Causes

A 
Collapse of plant
Erwinia atroseptica (Blackleg of potato)
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18
Q

Disease: canker

Causes

A 
Corky lesions on stems/roots/bark
Itersonilia perplexans (parsnips)
Stereum purpureum (plums)
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19
Q

Disease: leaf spots

Causes

A 
Necrotic lesions on leaves
Diplocarpon rosae (Rose blackspot)
Mycosphaerella graminicola (Septoria on wheat)
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20
Q

Disease: leaf and glume blotch

Causes

A

Poor seed quality

Stagonospora nodorium

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21
Q

Cause of seed infection

A

Claviceps purpurea

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22
Q

Disease: Downey mildew

Cause

A

(Oomycete) hyphae inside leaf, spores made outside

Perenospora parasitica

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23
Q

Disease: powdery mildew

Cause

A

Fungus outside except feeding structures

Blumeria graminis

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24
Q

Disease: rusts

Cause

A

Pustules of spores erupt through leaf or stem cuticle

Puccinia sp.

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25
Q

Disease: smuts and bunts

Causes

A

Black masses of spores in seeds, flowers and galls
Ustilago sp.
Tilletia caries

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26
Q

Disease: galls/distorted tissue

Causes

A

Nematodes
Agrobacteria (crown gall)
Gibberella fujikuroi
Witches brooms

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27
Q

Cause of grey mould

A

Botrytis cinerea

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28
Q

What plant diseases do viral agents cause?

A

Yellowing
Flower breaking
Mosaics
Stunting

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29
Q

Environmental Factors which can cause plant diseases

A
  • Temperature and light
  • Water availability (flood/drought)
  • Nutrient availability
  • Pollution (and pesticides/herbicides)
  • Soil type (pH and mineral content)
30
Q

What nutrients do plants need?

A 
Potassium
Phosphorus
Nitrogen
Magnesium
Manganese
Iron
Boron
31
Q

What does Mg deficiency cause?

A

Chlorosis

32
Q

What does Mn deficiency cause?

A

Grey flicking of leaves

If plants are supplied with the metal ions, the new plant cells will be healthy, but the grey cells will not recover

33
Q

What does frost damage do to potatoes?

A

Scorch on foliage

Necrosis of tubers

34
Q

What can uneven temperature do to tomatoes?

A

Cause blossom end rot (necrotic lesions on bottom of tomato)

35
Q

What can hail do to wheat?

A

Cause seed to be threshed out of ear/seed head

36
Q

What are the three components of the disease triangle?

A

Environment
Pathogen
Host

37
Q

Where can a pathogen invade a plant?

A 
Via: stomates, hydathodes, wounds (require free water)
Via vectors (insects, nematodes)
38
Q

Structure of plant cuticle?

A
  • Leaf cuticle: waxy later
  • Sub-cuticular layers: celluloses, hemicelluloses, pectates, proteins etc.
  • Plant cell walls
  • Dissolves extracellular enzymes
39
Q

What is an appressorium?

A

A specialised cell typical to many fungal plant pathogens that is used to infect host plants. Uses turgor pressure to punch through plant cuticle

40
Q

What are some diseases bacterial infections can cause?

A
  • Necrotic lesions on leaves
  • Soft rot of tissues
  • Fire blight
  • Scabs on fruit/tubers
  • Galls
  • Increased frost damage - ice nucleation
41
Q

Features of most bacteria which infect plants?

A

Gram-negative
Rod-shaped
Motile (flagellate)

42
Q

What plant causes wildfire in tobacco and how?

A
  • Pseudomonas syringe pv. tabaci
  • Tabtoxin produced, causing chloroform halos around the lesion beyond the spread of bacteria
  • Plant cells leak nutrients and water into apoplast, bacteria use these for growth
  • Pectic enzymes degrade the mid-lamella of walls, separating cells, giving soft tissue
  • Water-soaked lesions, rapidly turning necrotic
43
Q

What are the three factors in the disease triangle?

A

Host, environment and pathogen

44
Q

How do pathogens pass the plant cuticle?

A

Via stomates, hydathodes or wounds

Requires free water or a vector (Nematodes or insects)

45
Q

What are examples of diseases caused by bacterial pathogens?

A
  • Necrotic lesions on leaves
  • Soft rot of tissues
  • Fire blight
  • Scabs in fruit/tubers
  • Galls
  • Increased frost damage - ice nucleation
46
Q

Features of most bacterial plant pathogens and exceptions

A

-Gram-negative
-Rod shaped
-Motile (flagellates)
Exceptions: Streptomycetes and Corynebacterium

47
Q

Wildfire in tobacco

A
  • Caused by Pseudomonas syringe pv. tabaci
  • Produces tabtoxin, causing chlorotic halos around the lesion beyond the spread of the bacteria
  • Plant cell’s leak nutrients and water into the apoplast, bacteria use these for growth
  • Pectic enzymes degrade the mid-lamella of walls, separating cells, giving soft tissue
  • Water-soaked lesions, rapidly turning necrotic
  • Bacteria overwinter in soil, debris and on tobacco seeds
48
Q

What causes Fireblight in fruits such as apples in orchards?

A

Erwinia amylovora

49
Q

Fireblight in apples or pears

A
  • Insect transmission to nectaries, also wounds, stomates, lenticels
  • Rapid colonisation of vessels -spread through tissue
  • Little if any CWDE or toxin production
  • Canker on bark, oozing bacteria when humid
  • Dry, shrivelled fruit stay on tree
  • Produces amylovoran - an extracellular polysaccharide. Non-producers show reduced virulence
  • Trees look as scorched as if by fire damage
50
Q

What is Quorum sensing?

A

Method used by bacteria to communicate and coordinate their behaviour
Can be use to monitor size of bacterial population and coordinate efforts to infect

51
Q

What is a common signal molecule used by bacteria to communicate?

A

N-sculpt Homoserine Lactone (AHL)

52
Q

What do bacteria do if only a small concentration of AHL is being produced?

A

They exhibit ‘individual behaviours’

53
Q

What happens when there are sufficient levels of AHL present that they cross a threshold concentration?

A
  • It means there is a large enough population of bacteria for them to exhibit ‘group behaviour’
  • Gene expression begins in all bacteria, to produce a toxin and affect the plant to the highest degree
54
Q

Are signal molecules in Quorum sensing the same across species?

A

No, very limited cross-talk between species

55
Q

Bacterial soft rot example

A

Erwinia carotovora (aka Pectobacterium carotovorum)

  • Enter via wounds
  • Secrete massive amounts of CWDEs
  • Tissue collapse
  • Infection of nearby material
  • Problem in storage
  • Control by good hygiene
56
Q

What can tissue distortions due to hormone production cause?

A

Tumors, galls, cankers and “crazy roots”

57
Q

What does Agrobacterium tumefaciens do?

A
  • Natural genetic engineer
  • Transfers T-DNA into plant genome
  • Causes synthesis of opines (food for bacterium - strain specific)
  • Plant cell’s produce cytokines and auxin (triggers cells to reproduce and get bigger)
  • Hyperplasia and hypertrophy (galls)
  • Bacteria multiply within the gall
58
Q

How does agrobacterium find plants to infect?

A

Wounded plant cells give out chemical signals which the bacteria detects and uses flagella to swim towards

59
Q

What is T-DNA?

A

Transfer DNA
Transferred DNA of the tumour-inducing (Ti) plasmid of some bacterial species
Many genes including Opine and Cytokinine genes only expressed once in the plant cell

60
Q

What types of eukaryotes can cause plant diseases?

A

Protists and protozoans

61
Q

Examples of protists and protozoans

A

Myxomycetes
Plasmodiaphoromycetes
Oomycetes
(Fungus-like organisms, often motile)

62
Q

Example of amoebal slime mould

A

Physarum sp.

63
Q

Feautures of Physarum sp.

A

Relatively uncommon
Amoebal mass
Not serious but unsightly
Appear in warm wet weather

64
Q

How do amoebal cells infect plants?

A
  • Motile cell
  • Enters plant
  • Becomes MEGACELL
65
Q

What is a megacell and what happens to it during sporulation?

A

Multinucleate mass of cytoplasm but with one cell membrane
When sporulating it goes through ‘free cell formation’ meaning the megacell forms a membrane and wall around each nucleus, generating lots of small separate cells from within the one megacell

66
Q

Examples of amoebal (plasmodial) infections

A

Clubroot of brassicas

Hook-root of watercress

67
Q

Difference between resting spores and motile zoospores

A

Resting spores germinate if near roots

Motile zoospores search out roots

68
Q

What is hypertrophy?

A

Cell enlargement

69
Q

What is hyperplasia?

A

Cell division

70
Q

Symptoms of clubroot in brassicas

A 
Hypertrophy
Hyperplasia
Produce large swellings on roots
Plant continues to grow weakly
Plants susceptible to drought
71
Q

How long do the resting spores of Plasmodiophora brassicae last?

A

Over 10 years

72
Q

What is the solution to preventing spread of P. brassicae

A

Don’t grow brassicas

Treat fields with lime

Year 2 Biology Ellie M (10 decks)

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