Gardening Classes

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WELKOM

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WELCOME

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SEED INFECTION AND TRANSMISSION OF PLANT VIRUSES Speaker : Somesh Jha Advisor: Dr. B. N. Patel Date : 13 th July,2001

Seed infection and transmission of plant viruses: 

Seed infection and transmission of plant viruses Introduction Economic importance and significance Seed Seed infection Why all plant viruses are not seed transmitted? Types of viruses that are seed transmitted Seed health research activities Conclusion

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INTRODUCTION

Introduction : 

Introduction Seed - Basic input resource Virus transmission through seed - Highly significant in virus preservation and spread. Seed transmissible viruses - adverse effect on seed and crop health 18% of known plant viruses are seed transmitted

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SYMPTOMS ON PODS AND SEEDS OF COWPEA

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Economic importance and significance

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Seed transmission of viruses Epidemiological significance Introduction in new area Ecological significance Perpetuation Perennation Dissemination Barrier to world trade Direct loss to seed & crop Economic imp. & significance

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SYMPTOMS OF ULCV

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SOME IMPORTANT SEED BORNE VIRUSES Alfa- alfa mosaic Medicago sativa Barley stripe mosaic Hordeum vulgare Triticum aestivum Bean common mosaic Phaseolus vulgaris Vigna unguiculata Bean southern mosaic P. vulgaris Brinjal mosaic Solanum 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 mays Pea 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 SYMPTOMS

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SEED

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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

Seed infection: 

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 and embryo Seed transmission Reddy et al ., (1998)

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Seed Formation

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EMBRYO INFECTION Three Ways Through introduction of virus into the embryo sac by the male gametophyte Infected pollen grain Germination Pollen tube grows into Embryo Sac Release male gametes Infected gamete 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 early stage Infected ovule e.g. Soybean Mosaic Potyvirus (SMV) route of Soybean embryo infection by invasion of the ovules Dong 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 Transmission BCMV in bean Bravo and Pineda (1996)

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Why all plant viruses are not seed transmitted ?

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Why all plant viruses are not seed transmitted ? Factors preventing virus passage through seed to the next generation Inactivation of virus in the embryo Embryo High energy Phosphates Conc Medium Unfavorable No virus increase Sterility of infected gametes Virus Direct lethal effects Gametes 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 connection No 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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Types of viruses that are seed transmitted 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 suspensor Developing embryo Contd…

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Cross-communicative interaction between nuceller/integument cells & the endosperm and between the endosperm & interfacing embryo cells during embryogenesis. Integument transfer cells Endosperm Cellular/biochemical factors interacting with virions or viral RNA Viral genome Interactive signal Embryo invasion 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.) Kim Yul 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) Slovak Republic 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 % LMV Rajkumar 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

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Seed health research activities Several IARCs in the CGIAR system are working ICARDA 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) Pakistan seeds L. siceraria CGMMV K.D. Hyun and Lee. J. Myung seeds inactivated (2000), Korea Republic 70 ° C HW 70 ° C DH 75 ° C, 3 days

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CONCLUSION

conclusion: 

conclusion S eed infection & transmission is related to host-pathogen interactions. Only a minority of these interactions resulting in infection also result in seed transmission E ven low rates of seed transmission in conjunction with secondary spread by insect vectors can result in the introduction of viruses into new area and can produce viral disease epidemics C ytoplasmic connections between the mother plant and flower and then developing seeds may influence the seed infection I n 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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THANK U