Plant Viruses
John A. Walsh, School of Life Sciences
University of Warwick
1. What is a virus?
Viruses comprise a protein coat (capsid) and a nucleic acid (genome)
They are obligate intracellular parasites, growth / reproduction
outside living cells doesn’t occur
They have complete dependence on host cells
2. The different types of plant viruses
Flexuous rods
‘Spherical’ (icosahedral)
Tobacco mosaic virus
Turnip mosaic virus
Cauliflower mosaic virus
Rigid rods
X300000
Tobacco mosaic virus
The CP and CI proteins
10 Mature Potyvirus Proteins
P1
HC-Pro
PIPO
P3
CI
6K1
VPg Pro
NIb-Pol
6K2
Computer reconstructions of virus particle (virion)
structures
Tobacco mosaic virus
(TMV)
Tomato bushy stunt virus
(TBSV)
CP
RNA viruses
DNA
viruses
3.How are viruses
transmitted?
The most common vectors are insects
Aphids
Whitefly
Thrips
Leafhoppers
Other invertebrate vectors
Mites
Nematodes
Non-invertebrate vectors
Fungus
Olpidium brassicae
Protist
Spongospora subterranea
4. Diseases caused by
plant viruses
• Viruses can kill plants
• They can reduce the yield:
– weight
- quality
- infection by secondary pathogens
• Stop plants flowering
• Reduce vigour in perennial crops e.g. vines,
asparagus etc.
Quality effects
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Distorted plants / fruit
Blemishes on produce
Disorders
Stains (e.g. on beans)
Tumours
Flower / petal break
Turnip mosaic virus infecting cabbage
Turnip mosaic virus infecting cabbage
Turnip yellows virus (formerly Beet western yellows virus)
infecting cabbage
Botrytis – secondary pathogen
Turnip mosaic virus infecting cabbage – secondary pathogens
Turnip mosaic virus infecting cauliflower
Turnip yellows virus (formerly Beet western yellows virus) in lettuce
Beet mild yellowing virus infecting sugarbeet
Lettuce big-vein in lettuce
Tomato bushy stunt virus in tomato in Morocco
Zucchini yellow mosaic virus in courgette
Turnip mosaic virus infecting wallflower