Detail description about virus vector relationship

1. Virus-vector relationship
N. H. SHANKAR REDDY
Ph.D., Plant Pathology
Annamalai University

2. Terminology use in virus transmission
1. Acquisition access period
• Time for which a initially virus free vector is allowed to access a virus source and could if it desire
feed on that source.
2. Acquisition feeding period:
• Time period necessary for successful acquisition of the virus by its vector which then become
viruliferous
3. Inoculation access period:
• Time for which a virus carrying vector is allowed to access a virus free plant and could feed on it.
4. Inoculation feeding period:
• Time period for which a virus carrying vector appears to be feeding on a virus free plant to transmit
it.

3. 5. Transmission threshold or inoculation threshold or Inoculation access threshold:
• The minimum initial time period that a vector need to acquire a virus and inoculate it to the virus free
plant
6. Infective capacity or retention period of vector:
• Time period for which a vector carries/ retain/ transmit the virus to host plant and remain viruliferous.
7. Incubation period or latent period:
• The time period from the start of acquisition feeding period until the vector can infect the healthy plant
with the virus.

4. Watson & Roberts (1939) gave the basic concept of virus vector relationship
Based on virus retention time by the vector
• Non-persistent
• Persistent
• Semi-persistent (Sylvester, 1958)
Virus vector relationship is also based on Site of retention of the virus in vector
• Stylet borne
• Circulative
• Propagative
• Transovarial transmission

5. 1.Non-persistent Viruses- Stylet borne
transmission
• Such viruses are acquired by the vector during probing and feeding on host
parenchyma including epidermal cells
• Probing takes as little as 5 seconds.
• Vector becomes infective immediately after feeding
• Virus lost by the vector during moulting and No latent period
• Such viruses are mechanically transmissible
• Acquisition fasting increases acquisition o f virus and transmission.
• E.g. CMV, BCMV, PVY, PSBMV, PRSV, PMV

6. 2. Semi-persistant (Foregut –borne
transmission)
• Virus persist in its vector for 10-100 hrs.
• Acquired from phloem region with long feeding
• No latent period
• Do not circulate and multiply in its vector
• Infectivity lost in moulting
• High vector specificity
• E.g. CTV, CaMV, BYV (Beets yellows virus)
• The virus particles does not found in haemolymph or progeny of vector.
• In non persistant and semi persistant viruses these domines are in coat protein and
another protein called helper component

7. 3. Persistent viruses
• Virus persist in their vector for >100 hrs and in some cases for whole life of vector
• Virus multiply and circulate in vector body
• Latent period is present
• Moulting has no effect of virus
• After virus uptake-alimentary canal gut wall cirulates
• In the body fluid (Haemolymph) salivary glands causing contamination of saliva
transmission
• Also called as
i. Circulative
ii. Circulative propagative
iii. Trans-ovarial transmission
• E.g. PLRV, RDV, PYDV, BYDV
Note - transmission from parent to offspring via the ovaries

8. (i) Persistant circulative, non-propogative
transmission:
• Viruses passing from an insect gut into the haemolymph of the vector eventually
reaching the mouthparts in the saliva but not multiply in vector.
• The virus pass only to the circulative system from gut and back to salivary gland.
• Starving prior to acquisition doesn’t influence their ability to acquire.
• These cannot be usually sap or mechanically transmissible. All geminiviruses and
many leafhopper transmitted viruses.
• Eg - Beet curly top virus, maize streak virus and Wheat dwarf virus

9. (ii) Persistant circulative –propagative
transmission
• Plant viruses which are circulated and also multiply in them are propagative plant
viruses.
• The virus multiply both in plants as well as in insect vector There should be
evidence that the virus particles number should increase following acquisition by
vector
• Eg. Potato leaf roll virus(M. persicae)
• Wound tumor virus by leaf hopper- transoverially transmitted to off springs.
• Multiplication may occur in cytoplasm of cells of muscles, brain, fat bodies,
mycetome, trachae, epidermis and alimentary canal
• Some of the vectors suffer from diseases due to infection by viruses. These viruses
are considered to have been originating as insect viruses.
eg - Tomato spotted wilt virus transmitted by Thrips.

10. Differences

11. Video available at you tube
Channel – Geeky Researcher