In this presentation ' Transmission of plant viruses through Seed, Sap and vegetative propagation have been presented. Data is collected primarily from the Mathews plant virology book, however, part of it was also collected from the internet.

1. Transmission of Plant Viruses
through Seed, Sap and
Vegetative Propagation

2. Adil Zahoor
Department of Plant Pathology,
University of Agriculture
Faisalabad, Pakistan

3. Transmission ?
A process by which virus spread between hosts or
individuals of same host.
Horizontal
Transmission
The plant virus is
transmitted as a
result of an external
source i.e.
mechanical means,
plant cuttings.
Vertical
Transmission
The virus is inherited from a
parent plant, i.e. vegetative
reproduction, and seed
embryo infection by virus
infected plant.

4. Points should be noted
 Some being seed-borne on seed coat, but not seed
transmitted.
 RYMV (Rice yellow mottle virus) detected in seed
coat but does not transmit to host (Allarangaye et al.,
2006).
 Infectious viruses present in rice (glumella,
endosperm), lost their infectivity as seed matures (Konate
et al., 2001).
 PepMV (Papino mosaic virus) present in tomato seed
coat, infectivity of seedling 0.05 to 0.005 % (Ling, 2008;
Hansen et al., 2010).

5. Indirect invasion
Direct invasion
after fertilization
Johansen et al., 1994; Maule and Wang, 1996,
recommended two ways of virus invasion into seed.
Infection of developing embryo
before the fertilization due to
infected gametes is called indirect
invasion.
Direct infection of plant viruses to
embryo after the fertilization is
called direct invasion.

6. Points should be remembered:
 EPRV(endogenous pararetro viruses) can integrates into
the host genome, making progeny 100% infected.
Some Infections may cause symptoms on seeds.
SMV (Soybean mosaic virus) cause seed coat mottling in
soybean (Domier et al,. 2011).
Small seeds transmit PSbMV (pea seed-borne mosaic
virus) at higher rate than larger viral infected seeds of pea
plant (Khetarpal et al., 1988).

7. Factors Affecting The Proportion Of Infected Seed
1- Virus
Different viruses infect differently:
TRSV (tobacco ring spot virus) in soybean can infect 100%
(Athow and Bancroft, 1959).
In contrast, APLV(Andean potato latent virus) in potato can
infect 1% (Jones and Fribourg, 1977).
2- Viral determinants
Different isolates of a seed borne virus may show different
infection rates in the same host
(Bennet, 1969; Shepherd, 1972).

8. 3- Host Plant
TBRV (Tomato black ring virus) is seed transmitted in 9 different
plant species (Lister, 1960).
Some transmit with different rates in different hosts. i.e. AMV
(alfalfa mosaic virus) 10% in Melilotus indica and 2% in Stachys
arvenis.
4- Host resistance
 Soybean plant can control SMV by encoding enzymes through
DCL3 and RDR6 genes, involved in RNA silencing.
5- Time at which plant is infected
 In case of, infection through mother plant, earlier the plant is
infected higher the percentage of infection (Owusu et al., 1968).

9. Mechanism of Virus Transmission into Seed
Virus can get entry into seed through two ways
1-Mechanism of Gametic/indirect infection
Cytoplasmic connections between the infected mother plant,
flower and the developing seeds influence the seed infection.
In the process of seed development, food like, carbohydrates
moved into the seed as a food reserve along with virus.
legumes develop cytoplasmic connections more frequently than
cereals, the percentage of virus transmission through seeds in
legumes is higher than in cereals.

10. 1
Virus Infected Plant
4
Infection of gametes
2
Movement of food
contents from
infected to healthy
parts.
5
Formation of
infected seed.

11. 2- Mechanism of Direct Embryo infection
This mechanism has been studied in detail for pea seed-borne
mosaic virus (PSbMV) by Wang and Maule in1994.
Infection of testa of immature seed
Movement towards micropylar region
Micropylar has close contact with embryonic suspensor
Embryonic suspensor functions as nutrient flow to embryo
Transmission of virus in embryo.

12. Structure of Pea Seed

13. Typical Structure of a Flower

14. Plant Viruses Transmission through vegetative
Propagation
Asexual reproduction, in which a new plant grows from a
fragment of (such as a stolon, rhizome, tuber, corm, or bulb) other
parent plant.
Viruses are transmitted by the diseased vegetative parts such as
tubers, bulbs, roots, buds and scions which are used for propagation
e.g., mosaic and leaf curl of raspberry.

15. Plant Viruses Transmission through Sap
Occurs when plant come in contact with other plant and leaves
rub together.
 By the action of humans.
Involves the introduction of infective virus or biologically
active virus into a suitable site in the living cells through
wounds or abrasions in the plant surface.
 This method is generally used for experimental purposes
under laboratory conditions- also known as Sap inoculation.