pathogens/plant single-stranded positive strand RNA viruses


Potato X potexvirus
Lettuce mosaic virus

Single-stranded positive strand RNA plant viruses




Positive sense single stranded RNA [(+)ssRNA] are the most prevalent genomic type among plant viruses. The plus sense RNA viruses do not have envelopes and have monopartite, bipartite or tripartite genomes.

These viruses' genome may act as its own mRNA during replication cycle. After the viral particle enters the cell, (+)ssRNA molecule's uncoating occurs and translation of viral genes into proteins immediately begin on the host's ribosomes. After the proteins are generated, they are post-translationaly processed, if necessary, by self encoded proteinases. The viral RNA-dependent RNA polymerase and methyltransferase/helicase proteins then recruit host factors to form both subgenomic RNAs and progeny genomes. Coat proteins then envelope the progeny genomes to generate new viral particles.

Viruses - ssRNA viruses - ssRNA positive-strand viruses, no DNA stage -

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Potyviridae -

Organism Disease Transmission Management
Potyvirus - Plum pox virus
Synonyms plum pox virus, PPV; plum pox virus PPV; Plum pox potyvirus
Acronym: PPV
PPV, as a member of the genus Potyvirus, has a genome composed of a single stranded RNA molecule of near 10,000 nucleotides. Its expression strategy, similar to that of the rest of potyviruses, includes translation of a unique long open reading frame (ORF) further processed to yield viral products. Sharka (pox in Bulgarian) or plum pox disease, is considered one of the most devastating diseases of stone fruits. The disease causes reduced quality and premature dropping of fruits. While yellow or brown blotches or rings on the leaves or fruit of Prunus plants are characteristics of plum pox, other symptoms include severely deformed and bumpy fruit; leaf distortion and drop; and deformed, discolored seeds. Sometimes, infected trees display no symptoms on the leaves or fruit at all. In Chile and Pennsylvania, scientists discovered numerous, symptom-free orchards infected with PPV after confirming presence of virus with laboratory tests. The introduction of infected plant propagation material is considered the most important means of long distance spread of PPV. In addition, the virus is non-persistently transmitted by a number of aphid species existing in each region. At least 20 different aphid species (including Myzus persicae, Aphis spiraecola, A. gossypii, and A. fabae) can transmit PPV throughout an orchard and to other trees in nearby orchards, forests, and residential areas. Virus control in countries where the disease is not present are based on quarantine measures to avoid its introduction. In countries where the level of infection is low and infected trees are restricted to limited areas, eradication has made it possible to maintain a low level of infection and more rarely to eliminate the disease. Conventional breeding for sharka resistance has been hampered by the scarcity of resistant cultivars. The cultivar Honey Sweet plum now provides a unique source of germplasm for future breeding programs worldwide.
Potyvirus - Maize dwarf mosaic virus
Synonyms maize dwarf mosaic potyvirus
Misnomers: maize dwarf mosaic potyvirus MDMV; maize dwarf mosaic virus MDMV; Potyvirus Maize dwarf mosaic virus
Acronym: MDMV
MDMV has a single-stranded RNA of + polarity. The RNA is about 9,500 bp long and carries a VPg (viral genome-linked protein), which is covalently bound to its 50-end, and a poly(A) tail at its 30-end. The genome contains a long open reading frame (ORF) translated into a large 338 kDa polyprotein that is co- and/or post-translationally cleaved into 10 final protein products. This pathogen consists of 4 strains: C, D, E, and F. MDMV strains are known to infect maize, sorghum and Johnson grass. Symptoms appear six weeks after aphids feed and transmit this virus. Generally, infected plants develop distinct chlorotic mosaics, mottles or streaks on green tissues. Yield loss is caused by stunting and halting of ear formation and development. Aphids (both adults and nymphs) transmit the virus during feeding. The virus is acquired by the aphid within seconds of feeding and a latent period is not required for transmission to new host plants. Aphids do not retain the virus after molting. The virus overwinters in alternate hosts. Can also be transmitted to a lesser extent through seed and mechanically through plant damage. Mechanical transmission is considered to be a problem predominantly in greenhouses. Y Resistant varieties are widely available and offer the best means of disease management. Use of insecticides, biological control agents and cultural practices (management of aphid refuges) that reduce aphid populations will reduce transmission of viruses. Excessive use of nitrogen fertilizer favors aphid reproduction. Application of nitrogen above recommended levels should therefore be avoided. Removal of volunteer plants and management of alternate hosts, such as Johnson grass and graminaceous weed species, will reduce sources of inoculum. Use of certified, virus-free seed will limit seed-borne transmission of the MDMV and SCMV.
Potyvirus - Sugarcane mosaic virus
Synonyms sugarcane mosaic virus, SCMV; sugarcane mosaic virus SCMV; sugarcane mosaic potyvirus
Acronym: SCMV
One of the most widely distributed and important pathogens of sugarcane worldwide; consist of a large number of strains, differing from each other in certain biological and antigenic properties. The capsid protein is approximately 37 kDa in size. Amplification product (approximately 900 bp) can be obtained from the collected and inoculated plants but not from healthy plants which may confirm the presence of SCMV in the symptom-expressing plants. Mosaic is identified primarily by its leaf symptoms. Symptoms may vary in intensity with the cane variety, growing conditions, and the strain of the virus. The most distinctive symptom is a pattern of contrasting shades of green, often islands of normal green on a background of paler green or yellowish chlorotic areas on the leaf blade. The infection may be accompanied by varying degrees of leaf reddening or necrosis. There are three principal modes of spread of SCMV: (1) by aphid vectors, (2) by infected seed cane and (3) by mechanical inoculation. Only aphid vectors and infected seed cane are important in the field. Mechanical transmission, for the most part, is important only in greenhouse and laboratory research. The use of resistant varieties is the most effective method of control. Planting mosaic-free seed cane is essential. Management practices targeting insect vectors and control methods aimed at eradication have not been very effective. Also, the practice of destroying diseased plants is not considered feasible if the infection level exceeds 5%. Control of mosaic through heat treatment of cuttings is partially effective. It has been noted that some sugarcane plants recover from mosaic.
Potyvirus - Soybean mosaic virus
Synonyms soybean mosaic virus, SbMV; soybean mosaic virus SMV
Acronym: SbMV
Genome is a single-stranded, positive sense RNA molecule that is approximately 10 kb in length and contains a single open reading frame. It encodes a large polyprotein that is co- and post-translationally cleaved into 11 final protein products. SMV is found in all soybean-growing regions of the world. Data suggest a high genetic diversity of SMV. Most infected cultivars are slightly stunted with fewer pods that are sometimes dwarfed and flattened, without hairs, and without seeds. Leaves have a mosaic of light and dark green areas that may later become raised or blistered, particularly along the main veins. Primary leaves of some cultivars may show necrotic local lesions, which merge, into veinal necrosis followed by yellowing and leaf abscission. Seeds from infected plants may be mottled brown or black. Not all mottled seeds contain virus and not all seeds from virus-infected plants are mottled. The virus is transmitted by aphids and also seed-borne at a rate less than 5% in most varieties. SMV is sap and graft-transmissible. At least 32 aphid species, belonging to 15 different genera, transmit the SMV in a nonpersistent manner. Infected plants are primary inoculum sources for SMV. At least three resistance genes to SMV have been identified. At the present time, the use of SMV-free seed and avoiding late planting of soybean are the best control measures to preclude loss induced by SMV. Serological seed indexing techniques and/or grow-out tests can be used for virus detection in seed lots. Rouging, in addition to being generally impractical in the field, may not be very effective because of the tendency for symptoms in soybean to be masked above 30°C.
Potyvirus - Potato virus Y
Synonyms: potato virus Y, PVY; potato virus Y PVY; potato virus Y PVY-H
Acronym: PVY
Potato virus Y (PVY), the type member of the genus Potyvirus, is a major pathogen of solanaceous crops, such as potato, tobacco and pepper. Isolates of PVY largely differ by their pathogenicity properties in different host species and cultivars. Symptoms vary. Severe symptoms include dark brown, dead areas in the blade of nearly mature leaflets. Leaves formed after the onset of PVY exhibit mild wrinkling, slight distortion, and mild mottling. Leaflets of plants infected for some time are rolled downward with curved petioles (leafstalks), giving the plant a drooping appearance. PVY is transmitted in the nonpersistent manner by many aphid species. Aphids can acquire the virus in less than 60 sec. from an infected plant and transmit it to a healthy plant in less than 60 sec. The virus may be retained by the aphid for longer than 24 hours. PVY can also be transmitted mechanically. The virus does not appear to be seed transmitted. Strategies for controlling PVY include the following: eradication of all wild reservoir hosts in and around fields; early planting to avoid high aphid populations later in the season; rouging; monitoring aphid populations early in the season.
Potyvirus - Zucchini yellow mosaic virus
Synonyms: zucchini yellow mosaic virus, ZYMV; zucchini yellow mosaic virus ZYMV
Acronym: ZYMV
Misnomer: Zucchini yellow mosaic potyvirus ZYMV
A genome of 9,593 nt is arranged as a single open reading frame encoding a polyprotein precursor that is processed into 10 putative proteins. Of these, the coat protein (CP) is involved in the encapsidation of viral RNA, vector transmission, and the regulation of viral RNA amplification and cell-to-cell and systemic movement. Virions are flexuous filaments of 680–730 nm in length and 11–13 nm in diameter, composed of about 2,000 subunits of a single 31-kDa protein. A major pathogen of members of the family Cucurbitaceae. The main cultivated host species include rockmelon, cucumber, zucchini, pumpkin, watermelon, etc. Symptoms include yellowing, stunting, leaf deformations, and misshaped and discoloured fruits, which often renders the fruits unmarketable, drastically reducing agricultural yields. The leaf symptoms appear as severe mosaic, deformation, blistering, and reduced size. Both cucurbit and non-cucurbit aphids transmit ZYMV in the field and once the virus is introduced to a cucurbit planting its spread within the field is generally very rapid. ZYMV is seed-borne at low levels in zucchini and squash. Phytosanitary, cultural and biological control measures include: removal of potential virus and aphid sources among weeds, removing old crops, and avoiding overlapping and side-by-side plantings; deploying reflective or other plastic mulches to deter aphid landings and crop covers to prevent early aphid attaks; and using cross protection with mild ZYMV strains. In addition, host resistance genes against ZYMV have been described in some cucurbits. However, resistance breaking strains occur so resistance should never be used alone.
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Potyviridae -

Organism Disease Transmission Management
Bymovirus - Wheat yellow mosaic virus
Synonym: soil-borne wheat yellow mosaic virus
Acronym: WYMV
Misnomer: spindle streak mosaic virus (WSSMV)
Virions filamentous; not enveloped; usually flexuous rods; with two modal lengths of 275-300 nm, or 575-600 nm; 13-14 nm wide. Virions found in cell cytoplasm of all parts of the host plant. Spreads in Canada, China, France, Japan, Korea D.P.R. (North), and Korea Republic. Produces mosaic chlorotic to necrotic streaks. Symptoms typically appear in early spring. Also causes a mild stunting and reduced tillering. The field pattern of WSSMV tends to follow the lower, wetter areas of the field. Vectored by a fungus Polymyxa graminis, which also transmit Spindle Streak Mosaic Virus (WSSMV). Also transmitted by mechanical inoculation; not transmitted by contact between plants; not transmitted by seed; not transmitted by pollen. The virus particles are carried on or in the fungal zoospores. The fungus forms dark clusters of resting spores in the wheat roots which are released to the soil when the roots decay. Since the fungus survives in the soil as resting spores, the disease is always associated with infested soil. Soils may remain infective for at least 8 years. Susceptible cultivars should be avoided in fields infested with the pathogen. In addition, fields with WSBMV usually also have WSSMV. Late planting is sometimes effective in avoiding infection periods in the fall. Due to the longevity of the vector, crop rotation is not an effective control for WSSMV. Infection takes place at the time of wheat emergence in the fall, so avoid irrigation during this period if you have a susceptible variety.
Bymovirus - Barley yellow mosaic virus
Synonym: barley yellow mosaic virus, BaYMV
Acronym: BYMV
Is the type member of the genus Bymovirus, family Potyviridae. has slightly flexuous rod-shaped particles with two modal lengths of 550 and 275 nm and has a single-stranded, positive-sense RNA genome with two components of approximately 7.6 (RNA1) and 3.5 (RNA2) kb. The most widespread and economically important virus of winter barley in many countries. Causes serious damage to two-rowed barley crops. Symptoms vary seasonally. Symptoms yellow streaks especially on youngest leaves in winter or spring. Leaves may roll so the plants appear "spiky". Vigour reduced. Sometimes the leaves show complete yellowing with necrotic patches; plants are stunted. produced above 18°C. Vectored by a fungus Polymyxa graminis, which also transmit Spindle Streak Mosaic Virus (WSSMV). Virus transmitted by mechanical inoculation; not transmitted by contact between plants; not transmitted by seed; not transmitted by pollen. The virus particles are carried on or in the fungal zoospores. The fungus forms dark clusters of resting spores in the wheat roots which are released to the soil when the roots decay. Soils may remain infective for at least 8 years. Growing resistant barley cultivars is the only practical means to avoid damage in the absence of suitable chemical controls of the virus or its vector. Several resistant two-rowed barley cultivars have been developed and introduced; however, some of them have immediately become infected in several districts.
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Tymovirales - Alphaflexiviridae -

Organism Disease Transmission Management
Potexvirus - Potato virus X
Synonym: potato virus X, PVX
Acronym: PVX
Virions are flexuous, filamentous between 470 and 580 nm in length, built of subunits of a single coat protein (CP). Genome encodes 5 open reading frames (ORFs). The first ORF encodes viral replicase. The central region of the genome encodes three overlapping ORFs, known as the triple-gene block (TGB). Widely used as a vector for expression of genes in plants. At least four strain groups are recognized. Causes Potato latent disease. Occurs wherever potatoes are grown and produces weak to very weak symptoms (interveinal mosaic), which are often difficult to detect (latent). Only a few varieties react with necrosis. Causes only small yield losses, of up to about 10%. Other members of the family Solanaceae, such as tobacco, tomato and sweet pepper, may also be affected. In the field potato virus X is transmitted only by contact between diseased and healthy plants or by humans, animals or machines moving through the crop; it is not transmitted by aphids. Use approved seed potatoes when growing ware and starch potatoes and use high-grade stock seed when producing seed potatoes. Prevent transmission of the virus by machinery.
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Virgaviridae -

Organism Disease Transmission Management
Hordeivirus - Barley stripe mosaic virus
Synonym: barley stripe mosaic virus, BSMV
Acronym: BSMV
Members of the genus are typified by having tripartite genomic RNA, designated α, β, and γ, that are individually encapsidated as short rigid rods composed of 96% protein and 4% RNA. Infections appear as chlorotic mottling with spots or stripes of a yellowish color. Infected plants may be stunted and may mature later than healthy plants. Losses are caused by reduced grain production, fewer heads per plant, semi-sterility and incomplete head emergence from the sheath. Heavily infected crops have had yield reductions of up to 25%. S Seed-borne and is transferred from plant to plant when crop leaves rub against one another. Experimentally the virus can be transmitted by pollen, but since barley is self-pollinated this method of spread is generally of no consequence. Control measures include using virus-free seed; controling volunteer barley; not planting barley after barley if the previous barley crop was infected.
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Organism Disease Transmission Management
Sobemovirus - Rice yellow mottle virus
Acronym: RYMV
The capsid is composed of 180 identical capsid subunits that are closely interlinked through an exchange of the internal part of the coat making the virus particle very stable. The 4,450 nucleotides forming the RNA genome are organized into four ORFs which overlap (with the exception of ORF1) and code for four proteins. A major constraint of rice production in Africa with field losses more than 50%. The most important symptom is plant's leaves turning yellow, alternate yellow and green stripes give typical mottled appearance to the plant. Other symptoms include stunting, reduced tillering, incomplete panicle exersion, panicle malformations, and spikelet sterility. Virus enters plants through injuries, which may be inflicted by insects (which also act as vectors) or mechanically during the course of crop cultivation, for example damage to plants during hoe-weeding. The virus is particularly stable and seems to survive in particularly harsh weather conditions. In agronomically desirable rice varieties, there is virtually no source of resistance to RYMV. Integrated pest management (IPM) seems to be one of the best strategies in combating the virus.
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Luteoviridae -

Organism Disease Transmission Management
Luteovirus - Soybean dwarf virus
Acronym: SbDV
Viralicosahedral particles are 25 nm in diameter and contain one single-stranded positive-sense RNA. Genome contains five open reading frames (ORFs) and three untranslated regions, and it lacks both a poly(A) sequence at its 3' end and a 7-methyl GTP cap at its 5' end. Causes soybean dwarf, widespread in northern Japan and in other soybean-producing countries including U.S. where it infects red and white clover. Causes pronounced stunting in soybean with shortened internodes and brittle curled leaves. Yellowing strains cause severe interveinal chlorosis, rugosity and thickening of leaves. Transmitted persistently by at least six species of legume-colonizing aphids in a circulative, nonpropagative and often strain-specific manner. Included among the vector aphid species is Aphis glycines, which, since its initial discovery in 2000, has become a significant pest in North America. Cultural practices include roguing (removal of symptomatic plants); delayed sowing (to prevent viruliferous aphid vectors arriving from neighbouring virus sources); removal of cereal regrowths and stubble that can act as reservoirs of virus and vectors and the adoption of appropriate cultivation methods.
Luteovirus - Barley yellow dwarf virus
Synonym: barley yellow dwarf virus BYDV; barley yellow dwarf virus, BYDV
Acronym: BYDV
Virions are approx. 25 nm icosahedral (T = 3). One major (22 kDa) and one minor (50–55 kDa) coat protein. 5.6–5.8 kb positive sense RNA genome with no 5′-cap and no poly(A) tail. Distributed worldwide affecting nearly all members of Poaceae. Symptoms can be confused with other diseases and stress. Symptoms include yellowing and dwarfing in barley, stunting in wheat; reddening, yellowing and blasting in oats. Some isolates cause leaf notching and curling. Transmitted by more than 20 aphid species. The most important are the oat bird-cherry aphid, the corn leaf aphid, the English grain aphid and the green bug. Aphids acquire BYDV by feeding on infected plants and transmit the virus in subsequent feedings. Virus spreads by passive migrations of the winged form of the aphid vectors in cool (50° to 68° F), moist seasons. Disease symptoms usually occur about 2 weeks after infection. Control measures include delaying fall seeding of wheat until aphid populations decline; planting resistant or tolerant cultivars; growing diverse varieties to minimize the potential that a single variety will be severely affected by the disease; controlling grassy weeds and volunteer cereals, etc.. Chemical / Biological Control Fungicides have little or no effect on barley yellow dwarf.
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