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List the Two groups of Plant disease caused by viruses
- 1. Mosaics & mottles
- 2. Yellows
Characteristics of Mosaic and mottle viruses:
- Virus distributed throughout plant
- Non-persistent or semi-persistent
- Mechanical transmission
Characteristics of Bean common mosaic virus and Bean yellow mosaic virus
- Potyvirus group
- ssRNA, flexuous rods
- • Closely related
- cross-protection occurs
- • Mechanically transmissible
- • Non-persistent aphid transmission
- • Seed transmission - BCMV
How to control BCMV & BYMV
- Control aphid vectors
- Remove alternative hosts
- Healthy seed
- Genetic Resistance
Characteristics of Yellows diseases:
- Pathogen in phloem or xylem
- • Persistent transmission
- some propagative
- • Not mechanically transmissible
Why Study Transmission of Viruses?
- Experimentally, transmission of virus is an important component of recognition.
- o Economic impact is relative to transmission efficiency and crop lifetime.
- o Such knowledge is generally an important component of control measures.
- o Virus-vector relationships are of considerable biological interest.
- o Certain methods are essential for effective laboratory maintenance of viruses.
How are viruses transmitted?
- • Dodder
- • Plant propagules
- – True seed and pollen
- – Propagation materials
- • Soil-inhabiting organisms
- – Fungi, plasmodiophorids & nematodes
- • Arthropods (insects and arachnids –mites-)
Virus transmission by plant propagules
- – True seed
- •Seed transmission requires invasion of the
- embryo, and this occurs either by:
- •1) direct invasion of the embryo after
- fertilization or,
- •2) by indirect invasion of zygotic embryos
- through the fusion of infected gametes during fertilization.
Virus transmission by Soil-inhabiting organisms
- – Fungi
- • Chytridiales
- Olpidium brassicae Tobacco necrosis virus (TNV)
- – Plasmodiophorids
- • Polymyxa graminis
- Wheat yellow mosaic virus (WYMV)
- • Spongospora subterranea f. sp.
- subterranea (SSS)
- Potato mop top virus (PMTV)
- Longidorus spp.
- Paralongidorus spp.
- Xiphinema spp.
- Trichodorus spp.
- Paratrichorus spp.
Mechanical Transmission of viruses:
- =Manually transmitting a virus from one infected
- plant to another (healthy) plant
- •Possible ONLY in case of viruses that ARE
- mechanically transmissible
- •Example of a mechanically transmissible virus:TMV
- •Example of a mechanically NON-transmissible
- virus: Potato leaf roll virus
- =Manually transmitting a virus from one
- infected plant to another (healthy) plant
- •Why manual effort?
- •Virus are not capable of ‘active’ entry
- (unlike most fungi and bacteria)
- •Viruses ‘depend’ on ‘passive’ modes of entry
- (vectors, mechanical means such as cutting
What are the Steps in Mechanical Transmission
- •Grinding infected material in a suitable
- •*The buffer has to keep the virus from
- getting denatured or destabilized (loss of
- •Most commonly used buffer is neutral 0.05
- M phosphate buffer
- •Reducing agents such as mercaptoethanol,
- sodium sulfite help preserve the infectivity
- of the inoculum
- Carborundum or Celite are commonly used
- as abrasives (to create tiny wounds on leaf
- surface prior to application of the inoculum
- on healthy plants
- •Extract is gently rubbed on the dusted
- leaves of healthy plants
- •Excess inoculum is washed off with water
- •Plants kept at desirable temperature and
- lighting conditions in a greenhouse
- • Plants are observed on a regular basis for
- symptom development
- •Depending on the virus and host it may take 5 days to weeks before symptoms appear
How does BCMV survive?
Survives in seed or perennial legume hosts
How does BYMV survive?
Survives only in perennial hosts
Characteristics of Barley yellow dwarf virus (BYDV)
- Luteovirus group
- • ssRNA, spherical
- • Persistent, non-propagative transmission by
- • No mechanical or seed transmission
How to control BYDV
- Modify seeding date
- • Resistance
- barley, rye & oats
- • Control aphid vectors
- • Eliminate “green bridge”
What is the function of carborundum?
Used as an abrasive to help in grinding and causing wounding for viral infection
What is the purpose of using phosphate buffer in grinding?
To keep the virus from denaturing and help keep its infectivity
What is TSWV?
Tomato Spotted wilt virus
What is the Barley Yellow dwarf virus green bridge?
Winter wheat from sept to august, goes into spring wheat, spring barley or corn, then back into winter wheat