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Seed borne plant virus diseases

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  • 1. 2Identification and Taxonomic GroupsAbstractIn the early period of plant virus research work, inadequate identificationhas led to lot of confusion due to lack of an internationally acceptedclassification of plant viruses. The discriminatory criteria are establishedby ICTV study groups, who have followed the rules laid out in theInternational Code of Virus Classification and Nomenclature (ICVCN).As new types of viruses continue to be discovered, new names must becreated for taxa; several rules in the ICVCN govern the construction ofthese names.Till now, nearly 231 virus and viroid diseases are reported to beseed transmitted in different crop plants. As per the latest ICTV clas-sification by King et al. (Virus Taxonomy: 9th report of the interna-tional committee on taxonomy of viruses. Elsevier, San Diego, 2011),the seed-transmitted viruses were concerned to 231 virus families/plantvirus groups. Among these plant virus groups, seed-transmitted virusesare distributed in 24 virus groups including Alfamovirus, Bromovirus,Capillovirus, Carlavirus, Carmovirus, Caulimovirus, Comovirus, Cryp-tovirus, Cucumovirus, Enamovirus, Fabavirus, Furovirus, Hordeivirus,Ilarvirus, Necrovirus, Nepovirus, Potexvirus, Potyvirus, Sobemovirus, To-bamovirus, Tobravirus, Tombusvirus, Tospovirus and Tymovirus groups.Greater number of seed-transmitted viruses are found in Poty (35), Nepo(28), Crypto (28), Ilar (14), Tobamo (7), Potex (7), Como (6), Carla (5),Carmo (5), Cucumo (5), Sobemo (5), Furo (4), Bromo (3) and Tymo (3)virus groups. On the other hand, in some groups such as Alfamo, Capillo,Caulimo, Enamo, Faba, Hordei, Necro, Tobra and Tombus groups, theseed-transmitted viruses recorded were very few. No seed transmissionwas noticed in Clostero, Diantho, Gemini, Luteo, Marafi, Parsnip yellowfleck, Reo, Rhabdo, Tenui and Waika groups.K.S. Sastry, Seed-borne Plant Virus Diseases, DOI 10.1007/978-81-322-0813-6 2,© Springer India 201355
  • 2. 56 2 Identification and Taxonomic Groups2.1 IdentificationIn order to detect and identify a seed-transmittedvirus, it is imperative to understand thecharacteristics of seed-transmitted viruses forcomparison with the available information onpreviously described viruses. Diagnosis of avirus disease is never unequivocal unless thevirus is isolated, studied outside its host anddemonstrated by Koch’s postulates. By followingthe ‘ten commandments of the plant viruses’proposed by Bos (Bos 1976a), a reasonablediagnosis of the viral disease could be made.The diagnosis begins with particulars of thediseased plant and then deals with the virusitself, indicating a gradual shift from clinicalobservations to etiological diagnosis.The pragmatic approach depends on the factthat each virus has a definite host range that isoften confined to a wide or limited number ofhost plants. The natural hosts of the virus arefirst identified and a comparison is then madewith previously isolated species or their closerelatives, and their properties are also comparedwith those of the unknown virus. Based on themorphology of the virus involved, they can easilybe differentiated by their shape and size. Serologyand nucleic acid hybridisation tests are beingwidely used for the identification of differentplant viruses and their strains. At present thevirus identification is being done in scientificlaboratories through specialised techniques. Dif-ferent steps involve are seed morphology, indi-cator hosts, transmission, electron microscopy,serology, molecular methods, etc., which can helpin detection and identification of seed-transmittedviruses. The total list of conventional viruses,cryptic viruses and viroids which are seed trans-mitted and reported from different parts of theworld is presented in Table 1.2.2.2 Classification of VirusesIn the early period of plant virus research work,inadequate identification has lead to lot of con-fusion due to lack of an internationally acceptedclassification of plant viruses. Looking into thisproblem, Bos (1964) suggested the use of stan-dardised vernacular names while listing out theviruses from legume crops. Subsequent schemesof nomenclature (Gibbs and Harrison (1976);Matthews (1979, 1982); Fauquet et al. (2005);King et al. (2011) and grouping Harrison et al.(1971); Francki (1981)) of viruses and the recentCMI/AAB descriptions have contributed greatlyto the knowledge of plant viruses. During 1996,Brunt and his associates’ compiled publicationis one of the most important sources of descrip-tions of viruses of tropical plants. Information onthe identification of virus diseases in the formof Virus Information Data Exchange (VIDE) ispublished by Boswell and Gibbs 1986 and Gibbs1989. A system called ‘DELTA’ which is specif-ically designed to handle all forms of taxonomicinformation has been used to store the informa-tion in computers (Brunt et al. 1996).The taxonomic approach assesses the groupto which a virus belongs by determining someof its group-specific characteristics such as theshape and size of its particles. Then, more spe-cific tests including host range are used to checkwhether the unknown virus is an already de-scribed member of the likely group or not. Thisapproach requires some understanding in virusclassification. Modern taxonomic classification isalso taken into the consideration of molecularcharacterisation of viruses which has becomereliable and authentic (Van Regenmortal et al.2000; Fauquet et al. 2005; King et al. 2011). TheICTV 9th report of 2009 which was published byKing et al. (2011) has 6 orders, 87 families, 19subfamilies, 349 genera and 2,284 species.Based on a set of characteristics, more than975 plant viruses have been described and clas-sified by International Committee on Taxonomyof Viruses (ICTV) into 34 well-defined groupsand a few less well-defined groups or subgroups(Hamilton et al. 1981; Brown 1989; Martelli1992; Brunt et al. 1996; Fauquet et al. 2005; VanRegenmortel et al. 2005; King et al. 2011).In the Table 1.2, available informationon seed-transmitted virus diseases of fruits,vegetable and ornamental crops, including incollateral hosts, was listed along with percentageof seed transmission. In Table 2.1 taxonomicposition of seed-transmitted plant viruses is
  • 3. 2.2 Classification of Viruses 57Table 2.1 Taxonomic position of seed-transmitted virusesS. no Species (virus/viroid) Order Family Genus1 Alfalfa mosaic (Syn.) Berseem mosaic – Bromoviridae Alfamovirus2 Potato Yellowing – Bromoviridae Alfamovirus3 Alfalfa cryptic – Partitiviridae Alphacryptovirus4 Alfalfa temperate – Partitiviridae Alphacryptovirus5 Avocado viruses 1,2,3 – Partitiviridae Alphacryptovirus6 Beet 1 alpha crypto (Syn.) Beet temperate – Partitiviridae Alphacryptovirus7 Beet 2 alpha crypto – Partitiviridae Alphacryptovirus8 Beet 3 alpha crypto – Partitiviridae Alphacryptovirus9 Carrot temperate 1 – Partitiviridae Alphacryptovirus10 Carrot temperate 3 – Partitiviridae Alphacryptovirus11 Carrot temperate 4 – Partitiviridae Alphacryptovirus12 Fescue cryptic – Partitiviridae Alphacryptovirus13 Garland chrysanthemum temperate – Partitiviridae Alphacryptovirus14 Hop trefoil cryptic 1 – Partitiviridae Alphacryptovirus15 Hop trefoil cryptic 3 – Partitiviridae Alphacryptovirus16 Mibuna temperate – Partitiviridae Alphacryptovirus17 Radish yellow edge – Partitiviridae Alphacryptovirus18 Red clover cryptic – Partitiviridae Alphacryptovirus19 Red pepper cryptic-1 – Partitiviridae Alphacryptovirus20 Red pepper cryptic-2 – Partitiviridae Alphacryptovirus21 Rhubarb temperate – Partitiviridae Alphacryptovirus22 Rye grass cryptic – Partitiviridae Alphacryptovirus23 Santosai temperate – Partitiviridae Alphacryptovirus24 Spinach temperate crypto – Partitiviridae Alphacryptovirus25 Vicia cryptic – Partitiviridae Alphacryptovirus26 White clover cryptic 1 – Partitiviridae Alphacryptovirus27 White clover cryptic 3 – Partitiviridae Alphacryptovirus28 Pelargonium zonate spot – Bromoviridae Anulavirus29 Apple dapple viroid (Syn.) Apple scar skin viroid – Pospiviroidae Apscaviroid30 Grapevine yellow speckle – Pospiviroidae Apscaviroid31 Cucumber leaf spot carmovirus – Tombusviridae Aureusvirus32 Avocado sunblotch – Avsunviroidae Avsunviroid33 Banana streak – Caulimoviridae Badnavirus34 Cacao swollen shoot – Caulimoviridae Badnavirus35 Citrus mosaic – Caulimoviridae Badnavirus36 Citrus yellow mosaic – Caulimoviridae Badnavirus37 Kalanchoe top-spotting – Caulimoviridae Badnavirus38 Piper yellow mottle – Caulimoviridae Badnavirus39 Abutilon mosaic – Geminiviridae Begomovirus40 Carrot temperate 2 – Partitiviridae Betacryptovirus41 Hop trefoil cryptic 2 – Partitiviridae Betacryptovirus42 White clover cryptic 2 – Partitiviridae Betacryptovirus43 Broad bean mottle – Bromoviridae Bromovirus44 Brome mosaic – Bromoviridae Bromovirus45 Cowpea chlorotic spot virus – Bromoviridae Bromovirus46 Oat mosaic – Potyviridae Bymovirus47 Citrus tatter leaf – Flexiviridae Capillovirus(continued)
  • 4. 58 2 Identification and Taxonomic GroupsTable 2.1 (continued)S. no Species (virus/viroid) Order Family Genus48 Carlavirus Tymovirales Betaflexiviridae Carlavirus49 Clover (red) vein mosaic Tymovirales Betaflexiviridae Carlavirus50 Cowpea mild mottle Tymovirales Betaflexiviridae Carlavirus51 Pea streak Tymovirales Betaflexiviridae Carlavirus52 Red clover vein mosaic Tymovirales Betaflexiviridae Carlavirus53 Blackgram mottle – Tombusviridae Carmovirus54 Cowpea mottle – Tombusviridae Carmovirus55 Melon necrotic spot – Tombusviridae Carmovirus56 Muskmelon necrotic spot – Tombusviridae Carmovirus57 Pea stem necrosis – Tombusviridae Carmovirus58 Cauliflower mosaic – Caulimoviridae Caulimovirus59 Dahlia mosaic – Caulimoviridae Caulimovirus60 Citrus leaf blotch Tymovirales Betaflexiviridae Citrivirus61 Coconut cadang-cadang viroid – Pospiviroidae Cocadviroid62 Coleus blumei viroid 1 – Pospiviroidae Coleviroid63 Coleus blumei viroid 2 – Pospiviroidae Coleviroid64 Coleus blumei viroid 3 – Pospiviroidae Coleviroid65 Bean pod mottle Picornavirales Secoviridae Comovirus66 Broad bean true mosaic Picornavirales Secoviridae Comovirus67 Broad bean stain Picornavirales Secoviridae Comovirus68 Cowpea mosaic Picornavirales Secoviridae Comovirus69 Cowpea severe mosaic Picornavirales Secoviridae Comovirus70 Echtes Ackerbohnen mosaic(Syn. Broad bean true mosaic)Picornavirales Secoviridae Comovirus71 Muskmelon mosaic (Syn.)Squash mosaicPicornavirales Secoviridae Comovirus72 Pea mild mosaic Picornavirales Secoviridae Comovirus73 Red clover mottle comovirus Picornavirales Secoviridae Comovirus74 Strawberry pallidosis – Closteroviridae Crinivirus75 Banana viruses – Bromoviridae Cucumovirus76 Cucumber mosaic (Syn.)Cowpea banding mosaic (Syn.)Cowpea ring spot (Syn.)Soybean stunt– Bromoviridae Cucumovirus77 Peanut stunt – Bromoviridae Cucumovirus78 Tomato aspermy – Bromoviridae Cucumovirus79 Winged bean ring spot – Bromoviridae Cucumovirus80 Beet curly top – Geminiviridae Curtovirus81 Pea enation mosaic – Luteoviridae Enamovirus82 Broad bean wilt Picornavirales Secoviridae Fabavirus83 Nicotiana velutina mosaic – Virgaviridae Furovirus84 Peanut clump (Indian) – Virgaviridae Furovirus85 Wheat mosaic – Virgaviridae Furovirus86 Wheat soil-borne mosaic – Virgaviridae Furovirus87 Barley stripe mosaic(Syn.Barley false stripe)– Virgaviridae Hordeivirus88 Lychnis ring spot – Virgaviridae Hordeivirus(continued)
  • 5. 2.2 Classification of Viruses 59Table 2.1 (continued)S. no Species (virus/viroid) Order Family Genus89 Hop stunt viroid (Syn.)Cucumber pale fruit viroid(Syn.) Grapevine viroid– Pospiviroidae Hostuviroid90 Raspberry bushy dwarf (Syn.)Loganberry degeneration– – Idaeovirus91 Apple mosaic – Bromoviridae Ilarvirus92 Asparagus latent (Syn.)Asparagus virus II– Bromoviridae Ilarvirus93 Black raspberry latent – Bromoviridae Ilarvirus94 Elm mottle – Bromoviridae Ilarvirus95 Fragaria Chiloensis Ilarvirus – Bromoviridae Ilarvirus96 Humulus Japonicas – Bromoviridae Ilarvirus97 Hydrangea mosaic – Bromoviridae Ilarvirus98 Lilac ring mottle – Bromoviridae Ilarvirus99 Prune dwarf (Syn.) Cherry ringmottle (Syn.) Cherry yellows– Bromoviridae Ilarvirus100 Prunus necrotic ring spot(Syn.) Peach necrotic leaf spot(Syn.) Peach ring spot– Bromoviridae Ilarvirus101 Raspberry latent (Blackraspberry latent)– Bromoviridae Ilarvirus102 Spinach latent virus – Bromoviridae Ilarvirus103 Sunflower ring spot – Bromoviridae Ilarvirus104 Tobacco streak (Syn.)Asparagus stunt (Syn.) Beanred node (Syn.) Daturaquercina– Bromoviridae Ilarvirus105 Maize chlorotic mottlemachlomovirus– Tombusviridae Machlomovirus106 Olive latent virus-1 – Tombusviridae Necrovirus107 Tobacco necrosis – Tombusviridae Necrovirus108 Arabis mosaic Picornavirales Secoviridae Nepovirus109 Arracacha virus A Picornavirales Secoviridae Nepovirus110 Arracacha virus B Picornavirales Secoviridae Nepovirus111 Artichoke Italian Latent Picornavirales Secoviridae Nepovirus112 Artichoke yellow ring spot Picornavirales Secoviridae Nepovirus113 Australian Lucerne latent – Secoviridae Nepovirus114 Cacao necrosis Picornavirales Secoviridae Nepovirus115 Cherry leaf roll Picornavirales Secoviridae Nepovirus116 Cherry rasp leaf Picornavirales Secoviridae Nepovirus117 Chicory yellow mottle Picornavirales Secoviridae Nepovirus118 Crimson clover latent Picornavirales Secoviridae Nepovirus119 Cycas necrotic stunt Picornavirales Secoviridae Nepovirus120 Eucharis mottle Picornavirales Secoviridae Nepovirus121 Grapevine Bulgarian latent Picornavirales Secoviridae Nepovirus122 Grapevine fanleaf Picornavirales Secoviridae Nepovirus123 Hibiscus latent ring spot Picornavirales Secoviridae Nepovirus124 Lucerne (Australian)symptomlessPicornavirales Secoviridae Nepovirus(continued)
  • 6. 60 2 Identification and Taxonomic GroupsTable 2.1 (continued)S. no Species (virus/viroid) Order Family Genus125 Lucerne Australian latent Picornavirales Secoviridae Nepovirus126 Mulberry ring spot Picornavirales Secoviridae Nepovirus127 Peach rosette mosaic Picornavirales Secoviridae Nepovirus128 Potato virus U Picornavirales Secoviridae Nepovirus129 Raspberry ring spot Picornavirales Secoviridae Nepovirus130 Rubus Chinese seed-borne Picornavirales Secoviridae Nepovirus131 Satsuma dwarf Picornavirales Secoviridae Nepovirus132 Sweet potato ring spot Picornavirales Secoviridae Nepovirus133 Tobacco ring spot Picornavirales Secoviridae Nepovirus134 Tomato black ring Picornavirales Secoviridae Nepovirus135 Tomato ring spot (Syn.)Grapevine yellow veinPicornavirales Secoviridae Nepovirus136 Clover (red) mosaic Mononegavirales Rhabdoviridae Nucleorhabdovirus137 Coffee ring spot Mononegavirales Rhabdoviridae Nucleorhabdovirus138 Maize mosaic Mononegavirales Rhabdoviridae Nucleorhabdovirus139 Wheat striate mosaic Mononegavirales Rhabdoviridae Nucleorhabdovirus140 Citrus psorosis – Ophioviridae Ophiovirus141 Peach latent – Avsunviroidae Pelamoviroid142 Beet mild yellowing – Luteoviridae Polerovirus143 Carrot red leaf – Luteoviridae Polerovirus144 Chrysanthemum stunt viroid – Pospiviroidae Pospiviroid145 Citrus exocortis viroid – Pospiviroidae Pospiviroid146 Pepper chat fruit viroid – Pospiviroidae Pospiviroid147 Potato spindle tuber – Pospiviroidae Pospiviroid148 Tomato apical stunt viroid – Pospiviroidae Pospiviroid149 Tomato chlorotic dwarf viroid – Pospiviroidae Pospiviroid150 Tomato planta macho viroid – Pospiviroidae Pospiviroid151 Clover (white) mosaic Tymovirales Alphaflexiviridae Potexvirus152 Clover yellow mosaic Tymovirales Alphaflexiviridae Potexvirus153 Foxtail mosaic potexvirus Tymovirales Alphaflexiviridae Potexvirus154 Hosta virus x Tymovirales Alphaflexiviridae Potexvirus155 Pepino mosaic Tymovirales Alphaflexiviridae Potexvirus156 Potato virus X Tymovirales Alphaflexiviridae Potexvirus157 White clover mosaic Tymovirales Alphaflexiviridae Potexvirus158 Mung bean mosaic – Potyviridae Poty virus159 Artichoke latent – Potyviridae Potyvirus160 Asparagus virus I – Potyviridae Potyvirus161 Bean common mosaic (Syn.)Bean western mosaic (Syn.)Azuki bean mosaic– Potyviridae Potyvirus162 Bean common mosaic necrosis – Potyviridae Potyvirus163 Bean yellow mosaic – Potyviridae Potyvirus164 Blackeye cowpea mosaic – Potyviridae Potyvirus165 Bramble yellow mosaic – Potyviridae Potyvirus166 Broad bean mild mosaic – Potyviridae Potyvirus167 Cassia yellow spot (poty) – Potyviridae Potyvirus168 Celery latent – Potyviridae Potyvirus169 Cowpea aphid-borne mosaic – Potyviridae Potyvirus(continued)
  • 7. 2.2 Classification of Viruses 61Table 2.1 (continued)S. no Species (virus/viroid) Order Family Genus170 Cowpea green vein-banding – Potyviridae Potyvirus171 Cowpea moroccan aphid-borne mosaic – Potyviridae Potyvirus172 Desmodium mosaic – Potyviridae Potyvirus173 Guar symptomless – Potyviridae Potyvirus174 Hippeastrum mosaic – Potyviridae Potyvirus175 Leek yellow stripe – Potyviridae Potyvirus176 Lettuce mosaic – Potyviridae Potyvirus177 Maize dwarf mosaic – Potyviridae Potyvirus178 Onion yellow dwarf – Potyviridae Potyvirus179 Papaya ring spot – Potyviridae Potyvirus180 Pea mosaic (Syn. Bean yellow mosaic) – Potyviridae Potyvirus181 Pea seed-borne mosaic (syn. pea fizzle topand Pea leaf rolling virus)– Potyviridae Potyvirus182 Peanut mottle – Potyviridae Potyvirus183 Peanut stripe (Syn. Peanut mild mottle) – Potyviridae Potyvirus184 Plum pox virus – Potyviridae Potyvirus185 Potato virus Y (Syn.) Brinjal mosaic – Potyviridae Potyvirus186 Soybean mosaic – Potyviridae Potyvirus187 Sugarcane mosaic – Potyviridae Potyvirus188 Sunflower mosaic potyvirus – Potyviridae Potyvirus189 Telfairia mosaic – Potyviridae Potyvirus190 Turnip mosaic – Potyviridae Potyvirus191 Watermelon mosaic – Potyviridae Potyvirus192 Zucchini yellow mosaic – Potyviridae Potyvirus193 Bean southern mosaic (Syn. Southernbean mosaic)– – Sobemovirus194 Lucerne transient streak – – Sobemovirus195 Panicum mosaic – – Sobemovirus196 Sowbane mosaic – – Sobemovirus197 Subterranean clover mottle – – Sobemovirus198 Cucumber green mottle mosaic – Virgaviridae Tobamovirus199 Paprika mild mottle tobamovirus – Virgaviridae Tobamovirus200 Pepper mild mottle – Virgaviridae Tobamovirus201 Pepper mild mottle tobamovirus – Virgaviridae Tobamovirus202 Sunn-hemp mosaic (Syn.) Sunn-hemprosette– Virgaviridae Tobamovirus203 Tobacco mosaic – Virgaviridae Tobamovirus204 Tomato mosaic – Virgaviridae Tobamovirus205 Pea early browning – Virgaviridae Tobravirus206 Tobacco rattle – Virgaviridae Tobravirus207 Tomato bushy stunt – Tombusviridae Tombusvirus208 Tomato spotted wilt – Bunyaviridae Tospovirus209 Apple chlorotic leaf spot Tymovirales Betaflexiviridae Trichovirus210 Wheat streak mosaic – Potyviridae Tritimovirus211 Dulcamara mottle Tymovirales Tymoviridae Tymovirus212 Eggplant mosaic (Syn. Andeanpotato latent)Tymovirales Tymoviridae Tymovirus(continued)
  • 8. 62 2 Identification and Taxonomic GroupsTable 2.1 (continued)S. no Species (virus/viroid) Order Family Genus213 Melon rugose mosaic Tymovirales Tymoviridae Tymovirus214 Potato Andean latent Tymovirales Tymoviridae Tymovirus215 Turnip yellow mosaic Tymovirales Tymoviridae Tymovirus216 Sunflower rugose mosaic – Luteoviridae Umbravirus217 Cherry necrotic rusty mottle Tymovirales Betaflexiviridae Unassigned218 Potato virus T Tymovirales Betaflexiviridae Unassigned219 Strawberry latent ring spot Picornavirales Secoviridae Unassigned220 High plains virus – – Unassigned221 Urdbean leaf crinkle (Syn.)Black gram leaf crinkle (Syn.)bean urd leaf crinkle virus– – Unassigned222 Barley mottle mosaic – – Unassigned223 Brinjal ring mosaic – – Unassigned224 Brinjal severe mosaic – – Unassigned225 Carrot motley leaf – – Unassigned226 Cherry ring spot – – Unassigned227 Cineraria mosaic – – Unassigned228 Mung bean isometric yellowmosaic– – Unassigned229 Parsley latent – – Unassigned230 Peanut marginal chlorosis – – Unassigned231 Soybean mild mosaic – – Unassignedpresented by taking the information from Fauquetet al. (2005) and King et al. (2011) classificationtables. The seed-transmitted viruses are confinedto 34 virus groups, which are in Table 2.2. Tohave more clarity, the information on a particlemorphology and genome and vector is alsoprovided.Among these plant virus groups, 231 well-characterised seed-transmitted viruses aredistributed in 24 virus groups including Al-famovirus, Bromovirus, Capillovirus, Carlavirus,Carmovirus, Caulimovirus, Comovirus, Cryp-tovirus, Cucumovirus, Enamovirus, Fabavirus,Furovirus, Hordeivirus, Ilarvirus, Necrovirus,Nepovirus, Potexvirus, Potyvirus, Sobe-movirus, Tobamovirus, Tobravirus, Tombusvirus,Tospovirus and Tymovirus groups. Greaternumber of seed-transmitted viruses are foundin Potyvirus (35), Nepovirus(28), Cryptovirus(28), Ilarvirus (14), Tobamovirus (7), Po-texvirus (7), Comovirus (6), Carlavirus (5),Carmovirus (5), Cucumovirus (5), Sobemovirus(5), Furovirus (4), Bromovirus (3) and Tymovirus(3) groups (Tables 2.1 and 2.2). On the otherhand, in some groups such as Alfamovirus,Capillovirus, Caulimovirus, Enamovirus,Fabavirus, Hordeivirus, Necrovirus, Tobravirus,Tombusvirus and Tospovirus groups, the seed-transmitted viruses recorded were very few. Noseed transmission was noticed in Closterovirus,Dianthovirus, Geminivirus, Luteovirus, Parsnipyellow fleck virus, Reovirus, Rhabdovirus,Tenuivirus and Waikavirus groups.2.3 Variability in CertainSeed-Transmitted VirusesFrom the above discussed aspects on plant virustaxonomy, it is clear that the viruses resemblingeach other in genome properties and virion mor-phology are grouped into genera and given genusnames. The phylogenic analysis of some of theviruses indicates that recently described virusesare established based on molecular studies asstrains of the earlier described viruses. More
  • 9. 2.3 Variability in Certain Seed-Transmitted Viruses 63Table2.2Seed-transmittedvirusesindifferenttaxonomicgroupsofplantvirusesandtheircharacteristicfeaturesSl.no.Genus/groupTypememberParticlemorphologyParticlesize(nm)GenomeVectorNo.ofSeed-transmittedviruses1AlfamovirusAlfalfamosaicBacilliform28–5818ssRNAAphid22BromovirusBromemosaicIsometric26ssRNABeetle33CapillovirusApplestemgroovingvirusFlexuous64012ssRNA–14CarlavirusCarnationlatentvirusFlexuous620–70011ssRNAAphid,whitefly55CarmovirusCarnationmottlevirusIsometric28–30ssRNABeetle56CaulimovirusCauliflowermosaicvirusIsometric50dsDNAAphid27ClosterovirusBeetyellowsvirusFlexuousrods600–2,00010ssRNAAphid08ComovirusCowpeamosaicvirusIsometric28ssRNABeetle69CryptovirusSubgroupAWhiteclovercrypticvirus-1Isometric30ssRNA–25SubgroupBWhiteclovercrypticvirus-2Isometric38dsRNA–310CucumovirusCucumbermosaicvirusIsometric28dsRNAAphid511DianthovirusCarnationringspotvirusIsometric31–34ssRNA–012EnamovirusPeaenationmosaicvirusIsometric28ssRNAAphid113FabavirusBroadbeanwiltvirusIsometric30ssRNABeetle114FurovirusSoil-bornewheatmosaicRigidrods280–33020ssRNAFungus492–1602015Geminivirus0GroupAmastroMaizestreakvirusGeminate1830ssRNALeaf-hopper–GroupBbegomoAfricancassavamosaicGeminate1830ssRNAWhitefly–16HordeivirusBarleystripemosaicvirusRigidrods100–15020ssRNA–217IlarvirusTobaccostreakvirusIsometric26–35ssRNAThrips1418LuteovirusBarleyyellowdwarfvirusIsometric25ssRNAAphid019MarafivirusMaizerayadofinovirusIsometric31ssRNALeaf-hopper020NecrovirusTobacconecrosisvirusIsometric28ssRNAFungus2(continued)
  • 10. 64 2 Identification and Taxonomic GroupsTable2.2(continued)Sl.no.Genus/groupTypememberParticlemorphologyParticlesize(nm)GenomeVectorNo.ofSeed-transmittedviruses21NepovirusTobaccoringspotvirusIsometric28ssRNANematode2822ParsnipyellowfleckvirusParsnipyellowfleckvirusIsometric30ssRNAAphid023PotexvirusPotatovirusXFlexuousrods470–58013ssRNA–724PotyvirusPotatovirusYFlexuousrods680–90011ssRNAAphid,whitefly,mite3525Reovirus(a)PhytoreoWoundtumourvirusIsometric70dsRNALeaf-hopper0(b)FijivirusFijidiseasevirusIsometric71dsRNAPlant-hopper026RhabdovirusLettucenecroticyellowsvirusBacilliform160–38050–95ssRNAAphid,Leafhopper014–1142227SobemovirusSouthernbeanmosaicvirusIsometric28–30ssRNABeetle528TenuivirusRicestripevirusFlexuous>4008ssRNAPlant-hopper029TobamovirusTobaccomosaicvirusRigidrods30018ssRNA–730TobravirusTobaccorattlevirusShort&longrigidrods160–21522ssRNANematode214–1142231TombusvirusTomatobushystuntvirusIsometric30ssRNA–132TospovirusTomatospottedwiltvirusIsometric85ssRNAThrips133TymovirusTurnipyellowmosaicvirusIsometric29ssRNABeetle334WaikavirusMaizechloroticdwarfIsometric25ssRNALeaf-hopper0
  • 11. References 65examples one can find are in potyvirus group.Viruses like Blackeye cowpea mosaic and Peanutstripe virus are nothing but strains of the Beancommon mosaic virus with little variation. Vari-ability in viruses is noticed in almost all describedvirus groups. The molecular structure of viruseshas the capacity of transferring its characters toits duplicates produced in the host cells.(a) Hybridisation: This is one of the means bywhich new virus strains are formed. If twostrains of virus are inoculated into the samehost plant, one or more new virus strainsmay be recovered with properties (virulence,symptomatology, etc.) different from those ofeither of the original strains introduced intothe host. These new strains are probably hy-brids (RNA or DNA recombinants). Albersioet al. (1975) reported variability in Squashmosaic virus (SqMV) by hybridisation be-tween two strains of virus. They had crossedstrain 1 H and II A of SqMV in pumpkin(Cucurbita pepo) and cantaloupe (Cucumismelo) plants and observed the interactionbetween them.(b) Mutations: The evolution of new strains ofviruses may also be due to mutation. Thesemay be a heritable change in the geneticmaterial (RNA or DNA). The production ofmutants differing in virulence has also beenreported in several viruses, especially TMV,although they seem to vary mostly in thetype of symptoms and severity of disease theyproduce rather than in their ability to infectdifferent host plant varieties.The previous reports when the advanced iden-tification techniques were not available have re-ported very negligible (<1%) percentage of seedtransmission in certain virus–host combinations,which the later research workers have disproved.Without any discrimination based on the avail-able literature all the seed-transmitted viruses,Cryptoviruses and viroid diseases were reportedin the Tables 1.2, 2.1 and 2.2.In the earlier days, when the computerknowledge was not available, the students,research workers and others used to dependon Review of Plant Pathology, review articlesand other abstract journals for locating subjectliterature for use in their research work. Since1990, lot of databases and websites are availablewhich are quite useful for day-to-day plantvirus research work, where even the poorlibrary facilities existed and such problems weresolved by certain international organisations. Forexample, the ‘Crop Protection Compendium’(CPC), which was available on CD-ROM,was published by CAB International, whichis being updated annually on http://www.cabicompendium.org/cpc. Another valuableinformation source for viruses is of AABdescriptions on plant viruses and can be accessedon http://www.dpvweb.net. Even the descriptionsand lists from VIDE Database of the InternationalCommittee on Taxonomy of Viruses are availableon http://www.ncbi.nlm.nih.gov/ICTVdb/index.htm. ‘The Plant Pathology Internet Guide Book’(http://www.pk.uni-bonn.de/ppigb/ppigb.htm) isanother source of information for many virologytopics. Because of the availability of databasesof plant viruses on internet, it has become mucheasier for the virus research workers to know thelatest progress that is happening in any corners ofthe world (http://www.virology.net).ReferencesAlbersio J, Lima A, Nelson MR (1975) Squash mosaicvirus variability: nonreciprocal cross-protection be-tween strains. Phytopathology 65:837–840Bos L (1964) Tentative list of viruses reported from nat-urally infected leguminous plants. Neth J Plant Pathol70:161–174Bos L (1976a) Problems and prospects in plant virusidentification. EPPO Bull 6:63–90Bos L (1976b) Research on plant virus diseases in thedeveloping countries: possible ways for improvement.FAO Plant Prot Bull 24(4):109–118Boswell K, Gibbs A (1986) The VIDE data bankfor plant viruses. In: Jones RAC, Torrance L(eds) Developments and applications in virus test-ing. Association of Applied Biologists, Warwickshire,pp 283–287Brown F (1989) The classification and nomenclature ofviruses. Summary of results of meetings of Interna-tional Committee on Taxonomy of Viruses. Edmonton,Canada 1987. Intervirology 30:181–186
  • 12. 66 2 Identification and Taxonomic GroupsBrunt AA, Crabtree K, Dallwitz MJ, Gibbs AJ, WatsonL (eds) (1996) Viruses of plants. Description and listsfrom VIDE data base. CAB International, Wallingford,p 1484Fauquet CM, Mayo MA, Maniloff J, Desselberger U, BallLA (2005) Virus taxonomy, VIIIth report of the ICTV.Elsevier Academic Press, London, pp 751–756Francki RIB (1981) Plant virus taxonomy. In: Kurstak E(ed) Handbook of plant virus infection and compara-tive diagnosis. Elsevier, Amsterdam, 3Gibbs AJ (1989) A virus database for aiding plantpathologists. In: Proceedings of the 2nd meeting ofpeanut stripe virus coordinators, held at ICRISAT,Patancheru, IndiaGibbs AJ, Harrison BD (1976) Plant virology: the princi-ples. Edward Arnold, London, p 292Hamilton RI, Edwardson JR, Francki RIB, Hsu HT, HullR, Koenig R, Milne RG (1981) Guidelines for iden-tification and characterization of plant viruses. J GenVirol 54:223–241Harrison BD, Finch JT, Gibbs AJ, Hollings M, ShepherdRJ, Valenta V, Wetter C (1971) Sixteen groups of plantviruses. Virology 45:356–363King AMQ, Lefkowitz E, Adams MJ, Carstens EB (2011)Virus taxonomy: 9th report of the international com-mittee on taxonomy of viruses. Elsevier, San DiegoMartelli GP (1992) Classification and nomenclatureof plant viruses: state of the art. Plant Dis 76:436–442Matthews REF (1979) Classification and nomenclatureof viruses. Third report of the International Commit-tee on the Taxonomy of Viruses. Intervirology 12:131–296Matthews REF (1982) Classification and nomenclature ofviruses. Fourth report of the International Committeeon the Taxonomy of Viruses. Intervirology 17:1–199Van Regenmortal MHV, Fauquet CM, Bishop DHL,Carstens E, Estes M, Lemon S, Maniloff J, MayoM, Mc Geoch D, Pringle C, Wickner R (2000) Virustaxonomy: Seventh report of the International Com-mittee on Taxonomy of Viruses. Academic Press, NewYork/San DiegoVan Regenmortel HR, Bishop DHL, Van RegenmortelMH, Fauquet C (2005) Virus taxonomy: Eighth re-port of the International Committee on Taxonomy ofViruses. Academic Press, San Diego
  • 13. http://www.springer.com/978-81-322-0812-9