Histopathology of Seed-Borne Infections - Applied Research Center ...

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7Seed Infection by VirusesViruses are submicroscopic entities composed of a nucleic acid, ribonucleic acid(RNA), or deoxyribonucleic acid (DNA), surrounded by a protective protein orlipoprotein coat. They are acellular, but each virus has a characteristic shape, whichmay be a rigid rod, flexuous thread, spherical (polyhedral), or bacilliform (bulletshaped).One fourth of all known viruses cause diseases in plants. Plant virusesnumber about 2000, and new viruses are described regularly (Agrios, 1988). Approximately18 to 20% of the described plant viruses are seed-transmitted (Mathews,1991; Johansen, Edwards, and Hampton, 1994). Stace-Smith and Hamilton (1988)believe that one third of plant viruses will eventually prove to be seed-borne.Mathews (1991), Mink (1993), and Agarwal and Sinclair (1997) consider thatmost seed-transmitted viruses are carried within the embryo. The seed-borne andseed-transmitted viruses are listed in several publications (Bennett, 1969; Phatak,1974; Bos, 1977, Mink, 1993; Shukla, Ward, and Bunk, 1994; Agarwal and Sinclair,1997). Table 7.1 provides a list of seed-borne and seed-transmitted viruses, excludingcryptic viruses, using the nomemclature of the updated International Committee onTaxonomy of Viruses (ICTV) lists of 1995 and 1999. The cryptic viruses are listedseparately in Table 7.2. The occurrence of viruses in seed is shown in seed transmission,infectivity tests, and serological tests using whole seed or seed components.Histopathological investigations using TEM are few, but in recent years enzymelinkedimmunosorbent assay (ELISA), immunosorbent electron microscopy (ISEM),and molecular techniques have been used more frequently. Viroids, composed ofnaked single-stranded, low-molecular-weight, and circular RNA, were initiallytreated under viruses. They are also seed-borne and seed-transmitted. Table 7.3 liststhe most common seed-borne viroids. Histopathological information on seed infectionsby viroids is lacking at present.7.1 INFECTION AND MULTIPLICATIONViruses are unique as they multiply intracellularly. They enter cells through woundsmade mechanically, by vectors (insects, aphids, thrips, whiteflies, leafhoppers, beetles,mites, nematodes, and fungi), systemically through seeds, and by infected pollengrains. Ectodesmata have also been implicated as possible routes of infection forplant viruses (Brants, 1964; Thomas and Fulton, 1968). Outside the cell, viruses donot divide and are not known to produce any specialized reproductive structures.The viral parasitism is at the genetic level, using the internal cellular machineryduring its replication. They multiply by inducing the host cell to form more virusparticles, and in doing so, they disturb the normal cellular processes, upset the cellmetabolism, and prove injurious to functions and life of the host cell. Since viruses199
200 Histopathology of Seed-Borne InfectionsTABLE 7.1Seed-Borne Viruses Excluding Crypto-Viruses (Nomenclature as in the Reportsof the International Committee on Taxonomy of Viruses)Virus Name Acronym Genus Important Host (Genus)Alfalfa mosaic virus AMV Alfamovirus Medicago, Melilotus, Glycine,Nicandra, Solanum, CapsicumApple stem grooving virus ASGV Capillovirus MalusArabis mosaic virus ArMV Nepovirus Chenopodium, Capsella, Beta,GlycineArracacha virus B AVB Nepovirus SolanumArtichoke yellow ringspot AYRSV Nepovirus CyanaravirusAsparagus virus 2 AV-2 Ilarvirus AsparagusBarley stripe mosaic virus BSMV Hordeivirus Hordeum, Triticum, Avenaseveral other grainsBean common mosaic necrosis BCMNV Potyvirus Phaseolusvirus (serotype A of BCMV)Bean common mosaic virus BCMV Potyvirus Phaseolus, VignaBean pod mottle virus BPMV Comovirus GlycineBean yellow mosaic virus BYMV Potyvirus Lupinus, Vicia, Pisum, MelilotusBlackgram mottle virus BMoV Carmovirus VignaBlueberry leaf mottle virus BLMV Nepovirus Chenopodium, VitisBroad bean mottle virus BBMV Bromovirus Vicia, Cicer, Vigna, Phaseolus,PisumBroad bean stain virus BBSV Comovirus Vicia, Vigna, Pisum, LensBroad bean true mosaic virus BBTMV Comovirus ViciaBroad bean wilt virus 1 BBWV-1 Fabavirus ViciaBroad bean wilt virus 2 BBWV-2 Fabavirus ViciaBrome mosaic virus BMV Bromovirus TriticumCassia yellow spot virus CasYSV Potyvirus CassiaCherry leaf roll virus CLRV Nepovirus Prunus, Rhus, Sambucus,Juglans, Glycine, PhaseolusCherry rasp leaf virus CRLV Nepovirus Prunus, Chenopodium,TaraxacumChicory yellow mottle virus ChYMV Nepovirus CichoriumClover yellow mosaic virus ClYMV Potexvirus TrifoliumCocoa mosaic virus CoMV Nepovirus Glycine, PhaseolusCowpea aphid-borne mosaic CABMV Potyvirus Phaseolus, Vignavirus (South AfricanPassiflora virus)Cowpea green vein banding CGVBV Potyvirus VignavirusCowpea mild mottle virus CPMMV Carlavirus Vigna, Glycine, PhaseolusCowpea mosaic virus CPMV Comovirus VignaCowpea mottle virus CPMoV Carmovirus Vigna, Phaseolus(continued)
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Histopathology ofSeed-Borne Infecti
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PrefaceThe book deals with only one
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The AuthorsDalbir Singh, Ph.D., for
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ContentsChapter 1 Introduction ....
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4.3.2 Routes for Infection from Ova
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8.4 Survival in Seed ..............
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2 Histopathology of Seed-Borne Infe
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4 Histopathology of Seed-Borne Infe
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2Reproductive Structuresand Seed Fo
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Reproductive Structures and Seed Fo
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14 Histopathology of Seed-Borne Inf
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3Structure of SeedsThe seed habit i
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Structure of Seeds 49(1971) of usin
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Structure of Seeds 51is found in as
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Structure of Seeds 53dry seed of Ly
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Structure of Seeds 553.3.2 SEED COA
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Structure of Seeds 57Endosperm: One
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Structure of Seeds 59scendembepsmuA
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Structure of Seeds 61Endosperm: Sca
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Structure of Seeds 63Chalaza simple
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Structure of Seeds 65stystypmerA Bc
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Structure of Seeds 67epsent endCADB
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Structure of Seeds 69perhscendembpe
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Structure of Seeds 71eposgepi′epo
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Structure of Seeds 73(Zea and Sorgh
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Structure of Seeds 75Baker, D.M. an
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Structure of Seeds 77Maheshwari Dev
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Structure of Seeds 79Vries, M.A. de
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Page 163 and 164: TABLE 5.6Location of Mycelium of St
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Page 234 and 235: Seed Infection by Viruses 219seed(s
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Page 238 and 239: Seed Infection by Viruses 223REFERE
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