seed borne threats presented by somesh jha,m.sc.(agri.) during thesis seminar 2001

8/6/2019 Seed Borne Threats presented by Somesh Jha,M.Sc.(Agri.) during Thesis Seminar 2001

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SEED INFECTION AND TRANSMISSION OF

PLANT VIRUSES

Speaker : Somesh Jha

Guide: Dr. B. N. Patel

Date: 13th

July,2001


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Seed infection and transmission

of plant virusesIntroduction

Economic importance and significance

Seed

Seed infection

Why all plant viruses are not seed transmitted?

Types of viruses that are seed transmittedSeed health research activities

Conclusion


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INTRODUCTION


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IntroductionSeed - Basic input resource

Virus transmission through seed - Highly

significant in virus preservation andspread.

Seed transmissible viruses - adverse effect

on seed and crop health18% of known plant viruses are seedtransmitted


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SYMPTOMS ON PODS AND SEEDS OF COWPEA


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ECONOMIC IMPORTANCEAND

SIGNIFICANCE


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Seed transmissionof

viruses

Epidemiological

significance

Introduction in

new area

Ecological significance

Perpetuation Perennation Dissemination

Barrier to

world tradeDirect loss

to seed & crop

Economic imp. &

significance


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SYMPTOMS OF ULCV


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SOME IMPORTANT SEED BORNE VIRUSES

AlfaAlfa-- alfa mosaicalfa mosaic Medicago sativaMedicago sativa

Barley stripe mosaicBarley stripe mosaic Hordeum vulgareHordeum vulgare

Triticum aestivumTriticum aestivum

Bean common mosaicBean common mosaic Phaseolus vulgarisPhaseolus vulgaris

Vigna unguiculataVigna unguiculata

Bean southern mosaicBean southern mosaic P. vulgarisP. vulgaris

Brinjal mosaicBrinjal mosaic Solanum melongenaSolanum melongena


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SYMPTOM OF CABMV ON COWPEA


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Citrus mosaic Citrus sinensis

Cowpea mild mottle V. unguiculata

Glycine max

Cucumber green mottle mosaic Cucumis sativus

Lagenaria siceraria

Maize dwarf mosaic Zea maysPea seed borne mosaic Pisum sativum

Peanut clump Arachis hypogaea

Potato X S. tuberosum

Contd


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ULCV ON COWPEA

SYMPTOM


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Soyabean mosaic G. max

Tobacco etch Nicotiana tabacum

Tobacco ring spot N. glutinosa

Urdbean leaf crinkle P. aureus

Wheat streak mosaic Zea mays

Contd


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ULCV ON MUNGBEAN

S

Y

MPT

O

MS


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corn

Seed structure

Seed A fragile, living organism a miracle of life

(monocot seed)


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Seed structure

Bean (Dicot seed)


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Seed infection

VIRUS CARRIED ON THE SURFACE OF SEEDS

e.g. TMV Remains viable as contaminant

Seedling infection

Mechanical transmission during handling


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VIRUS CARRIED IN PARTS OF SEED

OUTSIDE THE EMBRYO

BYMV & CMV Testa & Endosperm

Sugarbeet Curly Top Virus Perisperm

Very few of such viruses result in seed transmission

Southern bean Mosaic Sobemovirus

IPCV Virus present only in cotyledons andembryo Seed transmission

Reddy et al., (1998)


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Seed Formation


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EMBRYO INFECTION

Three WaysThrough introduction of virus into the embryo sac by the

male gametophyte

Infected pollen grainGermination Pollen tube grows

into Embryo SacRelease

male gametes

Union with

egg cell

Infected

embryo

(if infected)

Union

with

polar

nuclei

Infected Endosperm

e.g. Tobacco Rattle Virus (TRV) & Alfa-alfa Mosaic Virus (AMV)


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SYMPTOMS


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Through ovule invasion by virus from the mother

plant

Adjacent cells

of mother

plant

(Infected)

Virus Developing

ovule in earlystage

Infected

ovule

e.g. Soybean Mosaic Potyvirus (SMV) route of Soybean

embryo infection by invasion of the ovulesDong Hong Ping et al., (1997)


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COLOUR DISCOLOURATION DUE TO SMV

SOYBEAN SEEDS


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Through direct invasion of the embryo

Inoculation

after flowering

Infected

embryo

e.g. PSbMV

Testa, Cotyledons Embryonic axis

& Cotyledons

Location & Embryonic

axis

TransmissionBCMVin bean

Bravo and Pineda (1996)


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WHY ALL PLANT VIRUSES ARE

NOT SEED TRANSMITTED ?

Factors preventing virus passagethrough seed to the next generation

Inactivation of virus in the embryo

Embryo High energyPhosphates Conc

Medium

Unfavorable

No virus increase

Sterility of infected gametes

VirusDirect

lethal effectsGametes or

embryo

Infected seeds

prevented

Low


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Inability of virus to infect young embryo

Virus restricted to

Vascular System

Embryo

Mother plant

No vascular connectionNo embryo

infection

Protection of the embryo from virus infection

Interposition of

structures between

the mother plant

& embryo

Embryo escapes

infection

No movement of

virus


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Other factors

Environmental factors

Host plant and virus

Nematode trans. Virus Seed trans.

e.g. tomato black ring virus

Listler and Murant (1967)

Longevity of Virus in seed

Varies one month (Dodder Latent Mosaic)

to >six years (Barley Stripe Mosaic)

Scott (1961)


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Types of viruses that

are seed transmitted


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Typesof virusesthat areseed

transm

itted

Certain general characteristics

Most are readily sap transmissible

Transmitted by certain types of vectors

e.g. Several non-persistent aphid transmitted viruses

Nematode transmitted viruses

Listler and Murant (1967)


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Three points of plant reproduction which

extrapolate virus trans. through seeds

A relatively long term conductive (embryo-supportive)function is ascribed to the developing suspensor

Infected

maternal tissue

Virions/

Viral RNA

suspensorDeveloping

embryo

Contd


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Cross-communicative interaction between

nuceller/integument cells & the endosperm and between

the endosperm & interfacing embryo cells duringembryogenesis.

Integument

transfer cellsEndosperm

Cellular/biochemical factors interacting with virions or viral RNA

Viral

genome

Interactive signal

Embryoinvasion

Host-plant

genome

VIRUS PASSAGE

Contd..


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Rate of seed transmission of some plant viruses

Chickpea 0.1-1.0 % 0.1-2.0 %

Lentil 0.1-5.0 % 0.1-2.0 %AMV CMV

Jones and Coutts (1995)

Australia

Soybean 12.6 % (mild mosaic sym.) KimY

ul Ho et al., (1997)Korea Republic

Mung bean 2.0-16.0 %

Urd bean 1.16-11.0%ULCV

Mahajan and Joi (1999)

Rahuri, India

14.1 % (severe mos. sym.)SMV

Pea 1.9-32.7 % (PSbMV) Gallo and Jurik (1995)

SlovakRepublic

Tomato 1.0-17.0 % (ToMV)

(Diff. Cult.)

Bell Pepper 1.0-10.0 % (TMV) Chitra et al., (1999)India


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Physalis minima 1.17 %Solanum nigrum 2.20 %Nicotiana plumbaginifolia 4.70 %

LMVRajkumar and Jitender

Mohan (1994), U.P.,

India

Cowpea 7.0-32.0 % 1.0-4.7% 1.0-3.0 %(V. unguiculata) BLCMV CPMV CPMMV

Nain et al., (1994)Hissar, India

Cowpea 3.0-25.0 % SBMV

Cowpea 10.0-30.0% CAbMV

Makwana et al., (2000)

Sheela et al., (2001)

Anand, India

Contd..


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Seed health research activities

Several IARCs in the CGIAR system are workingICARDA Effect of dry heat on lentil seeds

Heat treatment BBSV eliminated

Further plans with PSbMV and BYMV

CIP On PVT in true seeds

Reports

Soybean SMV eliminated Ghufran-ul-Haque et al., (1993)Pakistanseeds

L. siceraria CGMMV K.D. Hyun and Lee. J. Myung

seeds inactivated (2000), Korea Republic

70 C

HW70 C

DH

75 C, 3 days


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conclusion

Seed infection & transmission is related to host-pathogeninteractions. Only a minority of these interactions resulting ininfection also result in seed transmission

Even low rates of seed transmission in conjunction with secondaryspread by insect vectors can result in the introduction of viruses into

new area and can produce viral disease epidemics

Cytoplasmic connections between the mother plant and flower and

then developing seeds may influence the seed infection

In terms of world trade, seed-borne viruses act as barrier. Hence,

detection of seed-borne viruses has to play an important role in

quarantine.


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seed borne threats presented by somesh jha,m.sc.(agri.) during thesis seminar 2001

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