this chapter dealing about how the virus has enter in to the seed seed and what are all the factors involve the movement of virus

1. Mode of Entry and Establishment of
Virus in to Seed
K.Ramalingam
M.Sc., (Plant Pathology)
PAT 610 - Seed Health Technology (2 + 1)
TAMILNADU AGRICULTURALUNIVERSITY

2. overview
History
Mode Of Entry
 Contamination On Seeds
 Out Side Of Embryo
 Inside Embryo
 Direct Infection
 Indirect Infection (Ovule, Pollen)
Stage Of Infection
Genetics Of Seed Transmission
Virus Longevity In Seed.

3. History
Westerdijk (1910) and Allard (1914) – TMV in tomato
Annual Report Of Connecticut Agricultural Experiment Station (1915) - SMV
Stewart and Reddick (1917) – BCMV
1500 plant virus disease , 231 - virus , 24 - virus group
Alfamovirus, Bromovirus, Capillovirus, Carlavirus, Carmovirus,
Caulimovirus, Comovirus, Cryptovirus, Cucumovirus, Enamovirus, Fabavirus,
Furovirus, Hordeivirus, Ilarvirus, Necrovirus, Nepovirus, Potexvirus, Potyvirus,
Sobemovirus, Tobamovirus, Tobravirus, Tombusvirus, Tospovirus and
Tymovirus groups.

4. Surface of Seeds
Systemically infected plants transmit the virus as a surface contaminant of the
seed.
Very few viruses are qualify for transmission and causing disease.
1 – Stable to withstand in seed dehydration , harvest and storage .
2 – Able to enter in to seedling - transplanting , handling results in
mechanical inoculation .
way of entry :
 During germination the tiny abrasions caused by small
soil particles .
Ex: TMV, ToMV, PVX, CGMMV and Tomato bushy
stunt,

5. TMV as contamination
Chamberlain and Fry (1950)
compared uncleaned, fermented, and acid-extracted
seed with respect to virus content and seed transmission and
found that virus was transmitted by uncleaned seed, but not by
seed extracted by fermentation or by acid.

6. outside the Embryo
In the process of seed development, quantities of carbohydrates are
moved into the seed as a food reserve along with virus.
virus movement in the phloem is correlated with carbohydrate
transport, viruses that occur in high concentrations in the phloem
would be expected to move in considerable quantities into seeds that
have a vascular connection with the mother plant where they would
accumulate as food reserves are increased.
Ex. Sugarbeet curly top virus in perisperm

8. Inside The Embryo
Indirect invasion :
infection of reproductive tissue before embryogenesis.
Direct invasion :
infection of the embryo during some stage of embryogenesis.

9. Ovule infection by virus from pollen
Reddick (1931):
when flowers of healthy bean plants were pollinated from
infected plants, some of the resulting seeds transmitted virus, thus
proving that pollen may carry virus and transmit it to the
embryo.

10. Cont…
Seedborne TRSV was observed in the megagametophyte as well as in
pollen of soybean.
The high rate of seed transmission of TRSV in soybean was seemingly
related to the capacity of TRSV to invade meristematic tissue and
infect the megaspore mother cells.

12. Ovule Invasion by Virus from the Mother Plant
Fajardo (1928):
Reported that bean plants grown from seeds of plants infected
with bean mosaic virus gave higher percentages of infected seeds
than plants inoculated during stages of vegetative development
and that there was no virus transmission by seeds of pods set prior
to infection of the mother plant.

14. BSMV – Both Direction
Recording the cytological changes in the floral meristems during meiosis
and embryo formation in relation to the distribution of a seed-
transmitted strain (MI-1) and a non-seed-transmitted strain (NSP) in
the reproductive tissues.
The strain MI-1 - present in the megaspore and pollen mother cells as
well as in the egg and pollen,
the strain NSP was never found in these cells.
After fertilization, plasmodesmata were not observed between
developing embryos and the surrounding tissues.

15. Cont…
The presence of MI- l in megaspore and pollen mother cells preceded
the development of a callose layer and disappearance of
plasmodesmata separating megaspore mother cells and pollen
mother cells from parental tissues just before meiosis.
seed transmission was determined by the ability of BSMV to invade
male and female reproductive meristems very early in their
development, thereby infecting the embryo indirectly .

16. Callose layer

17. Direct Embryo Invasion
The pea cv. Vedette.
Movement of PSbMV in developing pods and seeds was monitored by
ELISA, immuno-cytochemistry, and in situ hybridization.
it was detected in the funiculus prior to fertilization, unfertilized
ovules.
After fertilization detected in the developing testa and endosperm and
in the embryonic suspensor.
pectocellulosic wall devoid of
plasmodesmata develop.

18. contact point between the testa and the suspensor was suggested as a
likely route of entry.
virus may be able to traverse the cell wall between the testa and the
suspensor by an as yet unidentified mechanism.
may be :
it may be able to induce formation of new plasmodesmata, thus
allowing direct invasion of the embryo.
The callose layer is incomplete around the newly formed embryo sac.

19. Pea seed-borne mosaic virus (PsbMV)

20. Stage of infection
Before flowering : TRSV in bean
cytoplasmic separation of the developing embryo from maternal
tissue . High transmission
Age of the plant : ULCV in urad bean

21. Genetics of seed transmission
Potyvirus genome-linked protein (VPg) – PsbMV.
CP and HC-Pro coding regions – PsbMV.
”b protein – BSMV.
physico–chemical properties and RNA secondary structure – TSV
(Mel 40 and Mel F).
Tripartite RNA particles – BSMV.

22. VIRUS LONGIVITY IN SEED
BCMV in bean seed - 30 - 36 years,
sowbane mosaic virus in Chenopodium murale for 14 years,
PNRSV in Prunus pensylvanica for 6 years.
Squash mosaic (SqMV) in Cucurbita pepo and TRSV in soybean for
over 5 years.
SMV and CpAMV - 2–3 years in legume seeds.
TMV in tomato seed - 9 years.

23. Bibliography
Subramanya Sastry (2013), Seed-borne Plant Virus Diseases,
springer,
Bennett w.c , Seed transmission of plant viruses,ars california
Elisabeth Johansen et al.,(1994) Seed transmission of viruses:
Current Perspectives, Annu. Rev. Phytopathol. 32:363—M
Paul Neergaard,(1969), seed borne disease, phytosanitory
inspection in Africa, 380-389
Yang A.F, Hamilton R.I (1974), The Mechanism of Seed
Transmission of Tobacco Ringspot Virus in Soybean, Virology 62,
26-37

24. Thanking you !!!