Mode of Entry and Establishment of Virus

in to Seed

K.Ramalingam

M.Sc., (Plant Pathology)

PAT 610 - Seed Health Technology (2 + 1)

TAMIL NADU AGRICULTURAL UNIVERSITY

overviewHistory

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.

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.

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,

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.

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

Inside The Embryo

Indirect invasion :

infection of reproductive tissue before embryogenesis.

Direct invasion :

infection of the embryo during some stage of embryogenesis.

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.

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.

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.

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.

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 .

Callose layer

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.

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.

Pea seed-borne mosaic virus (PsbMV)

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

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.

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.

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

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