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120-462: Potato virus Y (PVY) is a plant pathogenic virus of the family Potyviridae , and one of the most important plant viruses affecting potato production. PVY infection of potato plants results in a variety of symptoms depending on the viral strain . The mildest of these symptoms is production loss, but the most detrimental is 'potato tuber necrotic ringspot disease' (PTNRD). Necrotic ringspots render potatoes unmarketable and can therefore result in

240-472: A Chamberland filter-candle . This was in contrast to bacteria microorganisms , which were retained by the filter. Beijerinck referred to the infectious filtrate as a " contagium vivum fluidum ", thus the coinage of the modern term "virus". After the initial discovery of the 'viral concept' there was need to classify any other known viral diseases based on the mode of transmission even though microscopic observation proved fruitless. In 1939 Holmes published

360-435: A fluorescent dye . Direct correlation between signal strength and initial sample concentration is not possible using end-point analysis since PCR efficiency decreases as the reaction nears the plateau phase. Quantitative PCR , however, offers an accurate and rapid alternative to traditional PCR. Quantitative PCR offers the researcher the opportunity to amplify and analyze the product in a single tube using fluorescent dyes. This

480-484: A lipid envelope . This is derived from the plant cell membrane as the virus particle buds off from the cell . Viruses can be spread by direct transfer of sap by contact of a wounded plant with a healthy one. Such contact may occur during agricultural practices, as by damage caused by tools or hands, or naturally, as by an animal feeding on the plant. Generally TMV, potato viruses and cucumber mosaic viruses are transmitted via sap. Plant viruses need to be transmitted by

600-430: A reverse transcriptase enzyme to convert between RNA and DNA. 17% of plant viruses are ssDNA and very few are dsDNA, in contrast a quarter of animal viruses are dsDNA and three-quarters of bacteriophage are dsDNA. Viruses use the plant ribosomes to produce the 4-10 proteins encoded by their genome. However, since many of the proteins are encoded on a single strand (that is, they are polycistronic ) this will mean that

720-485: A vector , most often insects such as leafhoppers . One class of viruses, the Rhabdoviridae , has been proposed to actually be insect viruses that have evolved to replicate in plants. The chosen insect vector of a plant virus will often be the determining factor in that virus's host range: it can only infect plants that the insect vector feeds upon. This was shown in part when the old world white fly made it to

840-440: A "leaky" stop codon. In TMV 95% of the time the host ribosome will terminate the synthesis of the polypeptide at this codon but the rest of the time it continues past it. This means that 5% of the proteins produced are larger than and different from the others normally produced, which is a form of translational regulation . In TMV, this extra sequence of polypeptide is an RNA polymerase that replicates its genome. Some viruses use

960-412: A 20:2:1 solution of water, vinegar, and brown sugar can be used to trap and kill them. Farmers usually fight against the green peach aphid through efficacious cultural practices. Adjusting the planting layout; adjusting the sowing time and harvest time; deep plowing and winter turning over; appropriate use of crop fertilizers and timely drainage and irrigation can all be used to minimize the impact. It

1080-603: A DNA strand using the RNA as template. This results in a DNA/RNA complex. For synthesis of a DNA strand from the RNA template only the reverse primer is required since the RNA is a single strand arranged from 5’ to 3’. Subsequently, the newly synthesized DNA strand is used as a template for traditional PCR. Different types of reverse transcriptase polymerases are available to suit different needs and reaction conditions. Reverse transcriptase enzymes commonly used include AMV RT, SuperScript III, ImProm-II, Omniscript, Sensiscript and Tth RT. At

1200-701: A circle to form a disc. In the presence of the viral genome, the discs are stacked, then a tube is created with room for the nucleic acid genome in the middle. The second most common structure amongst plant viruses are isometric particles. They are 25–50 nm in diameter. In cases when there is only a single coat protein, the basic structure consists of 60 T subunits, where T is an integer . Some viruses may have 2 coat proteins that associate to form an icosahedral shaped particle. There are three genera of Geminiviridae that consist of particles that are like two isometric particles stuck together. A few number of plant viruses have, in addition to their coat proteins,

1320-528: A classification list of 129 plant viruses. This was expanded and in 1999 there were 977 officially recognized, and some provisional, plant virus species. The purification (crystallization) of TMV was first performed by Wendell Stanley , who published his findings in 1935, although he did not determine that the RNA was the infectious material. However, he received the Nobel Prize in Chemistry in 1946. In

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1440-607: A consequence of global warming has also led to an increase in aphid numbers, which in turn has led to an increase in viral distribution. PVY belongs to the genus Potyvirus , the largest genus of plant viruses and possibly the most destructive one in potato crops. The genus includes more than 200 species that bring about significant losses in the agricultural arena. PVY infects many economically important plant species. These include potato ( Solanum tuberosum ), tobacco ( Nicotiana tabacum ), tomato ( Solanum lycopersicum ) and pepper ( Capsicum spp.). The level of damage to crop

1560-401: A high-throughput technique for sample screening. Quantitative PCR has been described for detection and discrimination of PVY and PVY isolates and for reliable discrimination between PVY and PVY isolates. Plant virus Plant viruses are viruses that have the potential to affect plants . Like all other viruses, plant viruses are obligate intracellular parasites that do not have

1680-600: A mechanism similar to that used by eukaryotes. The extended open reading frame encodes for a 350 kDa polyprotein. This polyprotein is proteolytically processed by viral proteases (NIa, HC-Pro and P1) and undergoes co- and post-translational cleavage to yield several multi-functional proteins. These include the following: P1 (P1 Protein), HCPro (Helper Component Proteinase), P3 (P3 Protein), 6K1 (6-kDa Protein 1), CI (Cylindrical Inclusion), 6K2 (6-kDa Protein 2), VPg (Viral Protein genome-linked), NIaPro (Nuclear Inclusion Protein a, Proteinase domain), NIb (Nuclear Inclusion Protein b) and

1800-440: A minute piece of plant material is required for analysis using RT-PCR. Considering the protocol described within this thesis, 0.1 g of plant material is enough for 14 500 separate reactions. During a RT-PCR specific target RNA sequences are amplified exponentially into DNA copies. For this to occur, however, the RNA of the virus must first be transcribed to DNA by means of a reverse transcriptase polymerase. This polymerase synthesizes

1920-416: A more suitable host. Their lower efficiency as PVY vector is cancelled out by the sheer numbers in which they occur. Because of this, all aphids present in and around potato fields must be considered as possible vectors and their numbers carefully monitored. Transmission of PVY by aphids occurs in a non-persistent, non-circulative manner which suggests a less intimate interaction between virion and vector than

2040-492: A palm tree appearance (leaf drop). The viral defense mechanisms of plants will primarily try to restrict the movement of the virus. In failing this, it may attempt to induce cell death in infected tissue, thereby preventing the spread of virions. Although the precise mechanism of disease induction by potyviruses in plants is unknown, it is known that these viruses cause a significant shutdown of host gene expression during viral replication. Physiological changes in potato plants as

2160-486: A plant long term, Myzus persicae can uptake chloroplast DNA , even though the chloroplasts themselves are uninjured. Process of exudation from M. persicae stylets is exhibited to ingest phloem sap on plants with assisted pressure within the plants. On artificial diets, this species is also able to ingest food from a source with negligible pressure and can even produce honeydew on certain artificial diets. The green peach aphid has 2n=12 chromosomes normally, but there

2280-399: A premium on environmental protection and sustainable agriculture. Insect growth regulators like diflubenzuron , chlorbenzuron , and botanical pesticides like nicotine and azadirachtin also manage the orchard-pest ecology, reducing the number of the green peach aphids and the damage they cause. Similarly, the application of artificial insect pheromone or pest induction signal compounds in

2400-414: A quick, effective and sensitive method of screening for a wide range of potato plant viruses. Detection of pathogens using ELISA relies on the interaction between the antigen and specific antibodies and has become a popular and cost-effective means of routine detection. In an ELISA the solid phase can be coated with the sample of interest containing the antigen. The efficiency to which the antigen binds to

2520-401: A response to PVY infection were intensively studied. At early stages of infection, meaning first 12 hours, photosynthesis related genes, genes involved in perception, signalling and defence response were shown to be differentially expressed. 24 h after inoculation the amount of salicylic acid increased. A disruption in gene expression disrupts the normal cellular function of cells which could be

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2640-423: A significant loss of income. PVY is transmissible by aphid vectors but may also remain dormant in seed potatoes. This means that using the same line of potato for production of seed potatoes for several consecutive generations will lead to a progressive increase in viral load and subsequent loss of crop . An increase in potato plant infection with viruses over the past few years has led to considerable losses to

2760-559: A single sexual generation. Mating takes palace on the primary host, where eggs are laid and undergo diapause over winter, and when spring comes, the parthenogenetic females hatch in spring and their descendants disperse to secondary host plants where they produce numerous parthenogenetic (asexual) generations. This species accepts secondary host plants across 40 different families, many of which are important crops economically. Due to decreasing day lengths and temperature in autumn, sexual morphs of this species are formed. Some genotypes have lost

2880-472: A translocation between autosomes 1 and 3. This rearrangement is involved in the resistance to organophosphate and to carbamate insecticides. Hybridization can occur in these species in regions where the two forms have both a sexual phase on peach which may suggest why certain aphids have the same genes for insecticide resistance. There have been identifications of M. persicae populations with 13 chromosomes in various countries and diverse fragmentations of

3000-491: A virus common to peppers, the Pepper Mild Mottle Virus (PMMoV) may have moved on to infect humans. This is a rare and unlikely event as, to enter a cell and replicate, a virus must "bind to a receptor on its surface, and a plant virus would be highly unlikely to recognize a receptor on a human cell. One possibility is that the virus does not infect human cells directly. Instead, the naked viral RNA may alter

3120-412: A virus is given by its coat of proteins , which surround the viral genome . Assembly of viral particles takes place spontaneously . Over 50% of known plant viruses are rod-shaped ( flexuous or rigid). The length of the particle is normally dependent on the genome but it is usually between 300 and 500 nm with a diameter of 15–20 nm. Protein subunits can be placed around the circumference of

3240-790: A virus source outside these fields. Wingless aphids have not yet been linked to the spread of PVY in potato fields. The green peach aphid ( Myzus persicae ) has been found to be most effective in its role as viral vector, but others such as Aphis fabae , Aphis gossypii , Aphis nasturtii , Macrosiphum euphorbiae , Myzus (Nectarosiphon) certus , Myzus (Phorodon) humuli and Rhopalosiphum insertum are also strongly associated with viral transmission. The Agricultural Research Council-Vegetable and Ornamental Plant Institute (ARC-VOPI) 6 of South Africa identified twenty five species of aphid able to function as PVY vectors. The efficiencies of some of these aphids to function as PVY vectors were also established (Ragsdale et al., 2001) and were found to vary between

3360-458: A wide geographical scale by maintaining its primarily asexual life cycle. In GenBank, one genome from Myzus persicae has been assembled. It is found to have 17,086 genes and 99,545 nucleotides. RNAi ( RNA interference ) can impede pest reproduction which is why the understanding of this species genome is important. With this understanding, future methods of pest control can be conducted and controlled for. Under IUCN, and CITES no information

3480-598: Is PVY. This strain was described in tobacco plants growing close to potato plants. PVY results in leaf necrosis and mild or even no damage to the tubers. The ordinary strain of PVY is denoted as PVY. Infection of a potato plant with the PVY strain results in mild tuber damage and does not cause leaf necrosis. Both PVY and PVY are aphid transmissible and occur in South Africa. In Europe these two strains have been shown to have recombined to form PVY. The PVY has been accredited with

3600-404: Is a directly necessary part of the packaging of RNA viruses' genetic material . This was expected due to replicase involvement already being confirmed in various other viruses. The genome of Beet necrotic yellow vein virus (BNYVV) consists of five RNAs, each encapsidated into rod-shaped virus particles. RNA 1, which is 6746 nucleotides long, encodes a single open reading frame (ORF) that produces

3720-540: Is a form of a chromosomal translation seen worldwide that is relatively common. M. persicae is a highly variable species; strains, races and biotypes have been distinguished by morphology , color, biology, host-plant preference , ability to transmit viruses and insecticide resistance . This species is a great model for the study of chromosome arrangements since numerous variations regarding both chromosome number and structure have been reported. For instance, several populations of M. persicae were heterozygous for

Potato virus Y - Misplaced Pages Continue

3840-510: Is also a major vector for the transport of plant viruses and is known to be capable of transmitting over 100 different plant viruses, thus being the world's most versatile aphid viral vector. One useful control measure is to take advantage of the negative taxis the green peach aphid has; hanging silver-grey film or using silver grey film nets to cover field crops can inhibit their landing and settlement. Adults can be trapped by taking advantage of their preference for sweet or sour materials. Thus,

3960-401: Is approximately 23 days, without the presence of predators. The worst damage on plants is in the early summertime for the aphid breeding peak, because winged dispersants from Prunus spp. where the egg of overwintering aphid stage deposit nymphs on summer hosts migrating to tobacco, potatoes and cruciferous vegetables to be harmful continuously after a few generations. The green peach aphid

4080-418: Is associated with more severe symptoms. Plant viruses can be used to engineer viral vectors , tools commonly used by molecular biologists to deliver genetic material into plant cells ; they are also sources of biomaterials and nanotechnology devices. Knowledge of plant viruses and their components has been instrumental for the development of modern plant biotechnology. The use of plant viruses to enhance

4200-471: Is commonly believed that cypermethrin , abamectin , chlorpyrifos , methylamine and imidacloprid could be the first chemical agents for aphid control in the field. Although imidacloprid is a good insecticide for the control of pests who have piercing-sucking mouthparts, frequent reuse may lead to the severe resistance of pests. The application of plant secondary substances also plays a pivotal role in population control since people are increasingly putting

4320-480: Is cooled to between 40 and 70 °C to allow the primers to associate with their respective target sequences. This step is known as the annealing step and is primer specific. The temperature at which the primers anneal is critical. Too high temperatures would not allow the primers to associate with the DNA, resulting in no or poor amplification. Too low annealing temperature would ultimately lead to non-specific binding of

4440-522: Is determined by the strain of PVY infecting the plants, the viral load, the time at which infection occurs as well as the tolerance the host possesses toward the virus. Resistance to PVY infection by hosts is low in many cases. Infection of a potato field with PVY may ultimately result in 10–100% loss in yield. It has been shown that the PVY has different isolates according to the symptoms they induce in various potato plant species. Extensive biological, serological and molecular variability of PVY isolates makes

4560-573: Is found in terrestrial habitats, and as mentioned previously, its native range is likely of Asia-Temperate origin. Its European Nature Information System (EUNIS) habitat is classified as lines of trees, small anthropogenic woodlands, recently felled woodland, early-stage woodland and coppice. Eggs of this species measure about 0.6 millimetres (0.024 in) long and 0.3 millimetres (0.012 in) wide, and are elliptical in shape. The eggs are initially yellow or green but turn black. The nymphs are initially green, but soon turn yellowish and resemble

4680-419: Is found worldwide but is likely of Asian origin, much like its primary host plant, Prunus persica . This species does not prefer areas of extreme temperature or humidity. These particular aphids can be transported great distances by wind and storms. However, previous studies suggest that long-distance migration is uncommon in M. persicae , thus the spread of diverse genotypes over distance geographic regions

4800-454: Is in contrast to other aphid species that tend to specialize on a limited number of hosts, or consist of several host-adapted biotypes that specialize on a subset of the total host range. Through aphids sucking the phloem sap from plants, these plants can lose the nutrients and inhibit their growth and development. Its excreta (honeydew) accumulates on the leaves of crops, encouraging mold growth and affecting their growth and quality. This aphid

4920-404: Is known about the mechanisms involved in the transmission of plant viruses via seeds, although it is known that it is environmentally influenced and that seed transmission occurs because of a direct invasion of the embryo via the ovule or by an indirect route with an attack on the embryo mediated by infected gametes. These processes can occur concurrently or separately depending on the host plant. It

Potato virus Y - Misplaced Pages Continue

5040-457: Is known about the translation thereof, it is believed that the 5’ non-coding region functions as an enhancer of translation. The translated mRNA results in a polyprotein which is processed into mature proteins. Each polyprotein is then cleaved into ten different proteins which are believed to be multifunctional. These proteins, along with host proteins, assemble to form a replication complex. This complex performs negative-strand RNA synthesis, using

5160-465: Is known as homogeneous PCR. During a quantitative PCR the increase in fluorescence is correlated with the increase in product. Through the use of different specific, dyes quantitative PCR can be used to distinguish between different strains of a virus and even to detect point mutations. The major advantage of quantitative PCR is that analysis of resulting products using gel electrophoresis is not required. This means that quantitative PCR can be implemented as

5280-575: Is likely a result of anthropogenic influence. These insects are not only a pest towards field crops, but tend to invade greenhouses as well. Thus, when young plants are infested by these aphids in greenhouses and are then transported to other locations, they are widely distributed. This explains their great distribution lengths, as well as their ability of high survival in areas with inclement weather and their ability to be readily transported on plant material. This species has been introduced into 16 countries or islands (see global distribution figure). It

5400-411: Is more sensitive than ELISA, the reagents and instrumentation needed are expensive and require a higher level of technical expertise. Also, end product analysis using gel electrophoresis is laborious, relatively more expensive, time-consuming and does not lend itself to automation. For these reasons the use of RT-PCR for routine screening is not feasible and has not replaced ELISA. It does, however, provide

5520-667: Is normally adenine or guanine . The viruses encode a protein, normally a replicase , with a methyltransferase activity to allow this. Some viruses are cap-snatchers. During this process, a G-capped host mRNA is recruited by the viral transcriptase complex and subsequently cleaved by a virally encoded endonuclease. The resulting capped leader RNA is used to prime transcription on the viral genome. However some plant viruses do not use cap, yet translate efficiently due to cap-independent translation enhancers present in 5' and 3' untranslated regions of viral mRNA. Some viruses (e.g. tobacco mosaic virus (TMV)) have RNA sequences that contain

5640-426: Is particularly rich in adenine residues and has very few guanine residues. Rather than a conventional cap structure, the 5’NTR is associated with a Viral genome linked protein ( VPg ) which is said to act as an enhancer of transcription. The 5’-leader sequence has an internal ribosome entry site (IRES) and cap-independent translation regulatory elements (CIREs). The IRES directs cap-independent translation through

5760-416: Is present on their conservation status. Given that they are an invasive pest distributed worldwide, they are not a species of concern in terms of endangerment. The presence of the green peach aphid can be detrimental to the quality of the crops. In superfluous numbers, it causes water stress , wilt , and reduces the growth rate of the plant. Prolonged aphid infestation can cause an appreciable reduction in

5880-556: Is that changes at the gene level may have an influence on the immunogenicity of the antigen to be detected. In terms of potato plant viruses, mutations within the CP gene may cause the CP to undergo conformational changes rendering antibodies produced against the previously present virus less effective. Reverse transcriptase polymerase chain reaction (RT-PCR) has become a powerful and effective method for detection of potato plant viruses within potato plant material and even dormant potatoes. Only

6000-491: Is that the temperature required for DNA strand dissociation also results in DNA polymerase denaturation. This is partially overcome by the bioengineering of polymerases which are more thermal stable and have longer half-lives. Even though RT-PCR is technically more difficult to perform and more expensive than ELISA, it has the ability to allow for the detection of low viral loads. RT-PCR is considered to be 102 to 105 fold more sensitive than traditional ELISA. RT-PCR also allows for

6120-456: Is that they are highly absorptive and this increases the incidence of non-specific binding of components used in the ELISA. Non-specific binding to the plates is reduced through the use of buffers containing proteins such as casein and non-ionic detergents such as Tween 20. After coating, excess sample is removed and the plate typically treated with a 1% casein containing solution. Subsequent to this

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6240-647: Is the CaMV 35S promoter , which is a very strong promoter most frequently used in plant transformations . Viral vectors based on tobacco mosaic virus include those of the magnICON® and TRBO plant expression technologies. Building on the market approvals and sales of recombinant virus-based biopharmaceuticals for veterinary and human medicine, the use of engineered plant viruses has been proposed to enhance crop performance and promote sustainable production. Representative applications of plant viruses are listed below. Myzus persicae Myzus persicae , known as

6360-436: Is the case of circulative virions. The fact that the virions are transmitted in a non-persistent fashion means that viral replication does not occur within the aphid vector and that, unless the aphid feeds on infected plants, it loses its ability to infect plants after two to three feedings. The virions attach to the aphid stylet in a matter of seconds and may remain infectious for four to seventeen hours. The distance over which

6480-409: Is through the aphid, and although aphids on their own can directly damage potato plants, it is their role as viral vectors which has the greatest economic impact. In cold climates aphids spend the winter either as wingless aphids giving birth to live young (viviparae) or as eggs. Hosts such as weeds and other crops serve as breeding grounds for these aphids and form a temporary area of colonization before

6600-410: Is unknown how the virus is able to directly invade and cross the embryo and boundary between the parental and progeny generations in the ovule. Many plants species can be infected through seeds including but not limited to the families Leguminosae , Solanaceae , Compositae , Rosaceae , Cucurbitaceae , Gramineae . Bean common mosaic virus is transmitted through seeds. There is tenuous evidence that

6720-499: The Bromoviridae instead opt to have multipartite genomes, genomes split between multiple viral particles. For infection to occur, the plant must be infected with all particles across the genome. For instance Brome mosaic virus has a genome split between 3 viral particles, and all 3 particles with the different RNAs are required for infection to take place. Polyprotein processing is adopted by 45% of plant viruses, such as

6840-479: The Potyviridae and Tymoviridae . The ribosome translates a single protein from the viral genome. Within the polyprotein is an enzyme (or enzymes) with proteinase function that is able to cleave the polyprotein into the various single proteins or just cleave away the protease, which can then cleave other polypeptides producing the mature proteins. Besides involvement in the infection process, viral replicase

6960-498: The green peach aphid , greenfly , or the peach-potato aphid , is a small green aphid belonging to the order Hemiptera . It is the most significant aphid pest of peach trees, causing decreased growth, shrivelling of the leaves and the death of various tissues. It also acts as a vector for the transport of plant viruses such as cucumber mosaic virus (CMV), potato virus Y (PVY) and tobacco etch virus (TEV). Potato virus Y and potato leafroll virus can be passed to members of

7080-451: The 1950s a discovery by two labs simultaneously proved that the purified RNA of the TMV was infectious which reinforced the argument. The RNA carries genetic information to code for the production of new infectious particles. More recently virus research has been focused on understanding the genetics and molecular biology of plant virus genomes , with a particular interest in determining how

7200-508: The 237 kDa protein P237. This protein is cleaved into P150 and P66 by a papain-like proteinase. RNA 2, 4612 nucleotides long, encodes six proteins, including movement proteins (P42, P13, P15), a coat protein (P21), and a regulatory protein (P14). RNA 3, 1775 nucleotides long, encodes P25, which is involved in symptom expression. RNA 4, 1431 nucleotides long, encodes P31, crucial for vector transmission. RNA 5, found in certain isolates, encodes P26 and

7320-479: The 5’terminus and that the coat protein is built up towards the 3’terminus. The entire process of viral replication occurs within the endoplasmic reticulum . These newly synthesized viral particles are subsequently transported through the plasmodesmata to adjacent plant cells via several assisting potyvirus proteins. Distribution of viruses within the plant occurs according to the source-sink relationship between maturing and growing tissues. Virus concentration throughout

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7440-406: The CP (Coat Protein). In the past, crops were inspected visually to determine whether or not they were disease free. Visual inspection was also used as a basis for seed certification. Determination of viral status through visual inspection is incredibly difficult as the symptoms may be masked or the infection latent. As a result, post season tests and inspections were introduced. These tests involved

7560-466: The DNA-dependent polymerase component will start to amplify the target sequence. PCR amplification of the DNA target occurs in three steps: denaturation , annealing and extension. Each of these steps occur at a specific temperature for a fixed period of time. Denaturation is normally allowed to occur between 90 and 95 °C and leads to the dissociation of DNA strands. After this the reaction

7680-496: The South African potato industry. The increased rate of infection may be attributed to several factors. These include a marked decrease in the effectiveness and administration of chemicals used in vector control, the use of infected seed potatoes in cultivation, incorrect irrigation and farming methods as well as a lack of a sensitive, rapid and reliable method of detection. An increase in the average temperature of winters as

7800-477: The United States, where it transferred many plant viruses into new hosts. Depending on the way they are transmitted, plant viruses are classified as non-persistent, semi-persistent and persistent. In non-persistent transmission, viruses become attached to the distal tip of the stylet of the insect and on the next plant it feeds on, it inoculates it with the virus. Semi-persistent viral transmission involves

7920-401: The ability to induce potato tuber necrotic ringspot disease (PTNRD). Tubers damaged by PTNRD become unmarketable and infection by PVY thus results in a larger economic impact than infection by the other strains. PVY may be transmitted to potato plants through grafting , plant sap inoculation and through aphid transmission. The most common manner of PVY infection of plant material in the field

8040-434: The ability to sexually reproduce and thus reproduce through parthenogenesis on secondary hosts throughout the year. These types are known as obligate parthenogens. Host plants of this species during overwintering include tree hosts from the genus Prunus , particularly peach , peach hybrids and apricot and plum trees. During the summer, aphids abandon woody tree hosts for herbaceous hosts which include vegetable crops in

8160-458: The active center of the DNA polymerase is covered by dedicated oligonucleotides , called aptamers . At temperatures below the optimal reaction temperature of the DNA-dependent polymerase component of Tth remains covered by the aptamers. At these temperatures the Tth enzyme only synthesizes a DNA copy of the RNA template. Once the reaction temperature is raised to 95 °C, the aptamers are removed and

8280-419: The addition and detection of a biotinylated antibody. In a system using an enzyme-coupled antibody the subsequent addition of an appropriate substrate results in the formation of a colour proportional to the amount of antigen. Alternatively the plate can be coated with antibody followed by incubation with the sample that is to be detected. This, in turn, can be detected as described above and is then referred to as

8400-468: The aphids migrate to the potato fields. In moderate climates, such as in South Africa, aphids are thought to reproduce asexually on weeds, other crops, indigenous plants and garden plants. This means that there are a number of aphids present year-round. The importance in effective and stringent monitoring of aphid populations is stressed in a review by Radcliffe and Ragsdale (2002) as PVY virions are introduced to potato fields almost solely by winged aphids from

8520-428: The autosome (A) 3, suggesting that different naturally occurring rearrangements of the same chromosomes may be present in the aphid karyotype. The tobacco specialist subspecies, M. persicae nicotianae , known as the tobacco aphid, is a great example of speciation events that occur in the green peach aphid's evolutionary history. For instance, this subspecies has preserved its genomic integrity throughout time across

8640-406: The beauty of ornamental plants can be considered the first recorded application of plant viruses. Tulip breaking virus is famous for its dramatic effects on the color of the tulip perianth , an effect highly sought after during the 17th-century Dutch " tulip mania ." Tobacco mosaic virus (TMV) and cauliflower mosaic virus (CaMV) are frequently used in plant molecular biology. Of special interest

8760-908: The cause of the physical symptoms that the plant demonstrates. At the time of symptoms development, research on interaction between susceptible potato cultivar and PVY showed changes in cytokinin level. In inoculated leaves showing symptoms modifications in chloroplast structure and size, lower chlorophyll levels and differential activity of soluble and ionically bound peroxidases were detected. At later stages of PVY infection total protein concentration increased in sensitive potato cultivar while no such pronounced changes were observed in tolerant and moderately tolerant potato cultivars. Gene expression studies revealed changes in expression of genes for heat-shock proteins, catalase, β-1,3-glucanase and genes involved in photosynthesis. Potyvirus virions consist of non-enveloped filamentous structures that are 680 – 900 nm in length and 11 to 15 nm in width. Morphologically

8880-467: The chaperone protein symbionin , produced by bacterial symbionts . Many plant viruses encode within their genome polypeptides with domains essential for transmission by insects. In non-persistent and semi-persistent viruses, these domains are in the coat protein and another protein known as the helper component. A bridging hypothesis has been proposed to explain how these proteins aid in insect-mediated viral transmission. The helper component will bind to

9000-404: The classification of isolates as particular strains particularly difficult. Occurrence of a variety of symptoms and the emergence of the necrotic PVY has led to a search for more reliable classification tools than simple serological identification. Traditionally three chief strains of PVY are recognized: PVY, PVY and PVY. PVY, originally known as Potato Virus C , was the first to be recognized and

9120-461: The cultivation of previously harvested material in greenhouses. The resulting plants were inspected for a more accurate estimate of viral status. Although this method of screening did offer some degree of monitoring of viral presence it was subjective and highly ineffective. Enzyme-linked immunosorbent assay (ELISA) screening of crops and seed potatoes replaced visual inspection in the early 1970s. The use of ELISA offered routine diagnostic laboratories

9240-570: The detection of several viral targets in the same reaction through the use of several primer combinations. This is called multiplexing. Although multiplexing is technically more demanding than a traditional simplex reaction it allows for a higher throughput in that a single sample can be tested for several viral strains in a single reaction. Primers used for multiplexing are chosen in such a manner that they result in amplicons of various sizes. This allows for post RT-PCR analysis using gel electrophoresis. Although RT-PCR saves time, allows for multiplexing and

9360-760: The different species. In South Africa, Aphis fabae , Aphis gossypii and Aphis nasturtii are the most common and efficient PVY vectors found in the field. Apart from being classed according to efficiency as vectors, aphids can also be divided into two subgroups, namely colonizing and non-colonizing species. Colonizing aphids are aphids which reproduce and establish themselves on potato plants, specifically, while non-colonizing aphids do not reproduce nor establish colonies on potato plants. Colonizing aphids are better adapted to life on potato plants and are thus generally considered as better PVY vectors than non-colonizing aphids. Noncolonizing aphids do not primarily feed on potato plants but do occasionally feed on them while searching for

9480-442: The double antibody sandwich (DAS) ELISA. Both of these systems, however, have a disadvantage in that coupling of the enzyme to the antibody may result in steric hindrance which in turn may result in a loss in function of the antibody and/or the enzyme. This may be overcome through the use of a biotin-avidin or biotin-streptavidin bridge. In this type of system biotin is coupled to the antibody. The biotin molecule has no influence on

9600-573: The eggs hatch and nymphs feed on the flowers, young foliage and stems of the plant. After several generations, winged individuals deposit nymphs on summer hosts. In cold climates, adults will return to Prunus plants in the autumn, where mating occurs and eggs are then deposited. All generations except the autumn generation culminating in egg production are parthenogenetic (non-sexual). Females give birth to offspring 6–17 days after birth, with an average age of 10.8 days at first birth. Length of reproduction varies but averages 14.8 days. Average length of life

9720-454: The end of the RT step the polymerase enzyme is heatactivated. It could also be that the reverse transcriptase polymerase and DNA polymerase is one and the same enzyme and that the enzyme only requires a DNA polymerase activation step after the RT step. An example of such an enzyme is Tth polymerase. This enzyme has both RNA-dependent reverse transcriptase and DNA-dependent polymerase activity. However,

9840-408: The extension step the strands are amplified beyond the target DNA. This means that each newly synthesized strand of DNA will have a region complementary to a primer. There is an exponential increase in the amount of DNA produced as the three above mentioned steps are repeated in a cyclic fashion. In a traditional PCR these steps might be repeated 20 to 55 times. A problem, however, with PCR amplification

9960-504: The field to control pests and attract natural enemies has obtained effective results: E-β-farnesene (EβF), the aphid alarm pheromone, can interfere with aphid location and feeding, and also attract a variety of aphids' natural enemies to control the aphid population. Green peach aphids will transmit viruses to crops that they do not colonize, in which insecticides have little to no effect on virus transmission. Aphids are difficult to kill with contact insecticides because they are often under

10080-474: The first virus to be discovered. This and other viruses cause an estimated US$ 60 billion loss in crop yields worldwide each year. Plant viruses are grouped into 73 genera and 49 families . However, these figures relate only to cultivated plants, which represent only a tiny fraction of the total number of plant species. Viruses in wild plants have not been well-studied, but the interactions between wild plants and their viruses often do not appear to cause disease in

10200-466: The following families: Solanaceae , Chenopodiaceae , Compositae , Brassicaceae , and Cucurbitaceae . Crops differ in their susceptibility to green peach aphid, but it is actively growing plants, or the youngest plant tissue, that most often harbors large aphid populations. Once the aphids have established colonies, some redistribution may occur throughout the progress of the infestation, and before overcrowding obscures preferences. Natural enemies of

10320-441: The function of the cells through a mechanism similar to RNA interference , in which the presence of certain RNA sequences can turn genes on and off," according to Virologist Robert Garry. The intracellular life of plant viruses in hosts is still understudied especially the earliest stages of infection . Many membranous structures which viruses induce plant cells to produce are motile, often being used to traffic new virions within

10440-436: The green peach aphid include lady beetles , soldier beetles , hoverflies , acalyptrate flies , gall midges , flower bugs , leaf bugs , damsel bugs , stink bugs , lacewings , parasitic wasps , mites , fungal pathogens as well as other aphids. Many of the natural enemies of the green peach aphid are limited to them due to their certain chosen habitat or by unsuitability of other aphid species as food. Most enemies of

10560-458: The host plants, nutrition, and temperature. Distinguishing morphological traits from this group include their convergent inner faces of the antennal tubercles in dorsal view, and the slightly clavate siphunculi which are dark-tipped and approximately as long as the terminal process of the antenna. The green peach aphid normally reproduces through cyclical parthenogenesis, where there are several generations of apomictic parthenogenesis followed by

10680-691: The host plants. To transmit from one plant to another and from one plant cell to another, plant viruses must use strategies that are usually different from animal viruses . Most plants do not move, and so plant-to-plant transmission usually involves vectors (such as insects). Plant cells are surrounded by solid cell walls , therefore transport through plasmodesmata is the preferred path for virions to move between plant cells. Plants have specialized mechanisms for transporting mRNAs through plasmodesmata, and these mechanisms are thought to be used by RNA viruses to spread from one cell to another. Plant defenses against viral infection include, among other measures,

10800-483: The industry with the opportunity to screen borderline cases, especially in the case of seed potato certification. In most traditional PCRs the resulting products are analyzed after the PCR has been completed. This is called end-point analysis and is normally qualitative of nature rather than being quantitative. For this sort of analysis, products are mostly analyzed on an agarose gel and visualized using ethidium bromide as

10920-584: The infection of the sap was destroyed when it was boiled. He thought that the causal agent was bacteria. However, after larger inoculation with a large number of bacteria, he failed to develop a mosaic symptom. In 1898, Martinus Beijerinck, who was a professor of microbiology at the Technical University the Netherlands, put forth his concepts that viruses were small and determined that the "mosaic disease" remained infectious when passed through

11040-780: The insect cell by receptor-mediated endocytosis . Soil-borne nematodes have been shown to transmit viruses. They acquire and transmit them by feeding on infected roots . Viruses can be transmitted both non-persistently and persistently, but there is no evidence of viruses being able to replicate in nematodes. The virions attach to the stylet (feeding organ) or to the gut when they feed on an infected plant and can then detach during later feeding to infect other plants. Nematodes transmit viruses such as tobacco ringspot virus and tobacco rattle virus . A number of virus genera are transmitted, both persistently and non-persistently, by soil borne zoosporic protozoa . These protozoa are not phytopathogenic themselves, but parasitic . Transmission of

11160-418: The lesser understood area of plant viruses. 75% of plant viruses have genomes that consist of single stranded RNA (ssRNA). 65% of plant viruses have +ssRNA, meaning that they are in the same sense orientation as messenger RNA but 10% have -ssRNA, meaning they must be converted to +ssRNA before they can be translated. 5% are double stranded RNA and so can be immediately translated as +ssRNA viruses. 3% require

11280-635: The molecular machinery to replicate without a host . Plant viruses can be pathogenic to vascular plants ("higher plants") . Most plant viruses are rod-shaped , with protein discs forming a tube surrounding the viral genome ; isometric particles are another common structure. They rarely have an envelope . The great majority have an RNA genome, which is usually small and single stranded (ss), but some viruses have double-stranded (ds) RNA, ssDNA or dsDNA genomes. Although plant viruses are not as well understood as their animal counterparts, one plant virus has become very recognizable: tobacco mosaic virus (TMV),

11400-803: The nightshade/potato family ( Solanaceae ), and various mosaic viruses to many other food crops. Originally described by Swiss entomologist Johann Heinrich Sulzer in 1776, its specific name is derived from the Latin genitive persicae, "of the peach". The syntype specimen of this species is located in the Illinois Natural History Survey Insect Collection. Life cycle of the green peach aphid varies depending on temperature. A fully completed generation takes approximately 10 to 12 days with over 20 annual generations reported in mild climates. Aphids overwinter on Prunus plants and once plants break their dormancy,

11520-455: The pathogen. The ELISA is considered to be a safe, inexpensive and rapid method for detection of plant viruses. The inexpensive nature and relative simplicity thereof allows for it to be used as a workhorse within the agricultural sector and is used to screen thousands of samples per year. Unfortunately ELISAs are not completely failsafe. Virus levels within potato tubers, which are screened by ELISA for use as seed potatoes, are normally low while

11640-402: The peach green aphid are general predators that move freely in nearby habitats. Many of their enemies are influenced by the host plant, crop cultural practices and environmental conditions. Some groups of aphids feed predominantly in the parenchymal tissue of plants while most aphid species feed on the phloem sap. The green peach aphid ingests sugary fluids via a membrane. While feeding on

11760-448: The plant is high and this greatly increases the chance of uptake by aphids. Infection of plants by potyviruses can be varied in the symptoms shown. Infection can include veinal necrosis, mosaic symptoms as well as leaf malformation (Boonham et al., 2002). Infected plants that do not show symptoms may have infected canopies and will yield lower quality products than their healthy counterparts. Since PVY causes great loss in potato production,

11880-410: The positive strand of viral RNA as a template. Once the additional RNA copies have been produced, they code for the synthesis of various proteins, as mentioned before, as well as coat proteins. These coat proteins will now enclose the newly formed genomes to give rise to new virions . It has been suggested that enclosure of the newly formed virions is initiated by the interaction of the coat proteins with

12000-401: The potyvirus capsid consists of approximately 2 000 copies of coat protein (CP). The capsid encapsulates a single strand of positive sense RNA which is in the order of 10 kb in length and has a non-translated 5’-terminal region (5’-NTR) as well as a 3’-poly-A tail . The positive sense genome contains a single extended open reading frame and acts directly as mRNA. The 144 nucleotide 5’-NTR

12120-419: The primers and non-specific amplification. Primers bound to the regions flanking the target DNA provide 3’-hydroxyl groups for DNA polymerase catalyzed extension. The most commonly used DNA polymerase is Taq , a thermo-stable enzyme isolated from the thermophilic bacterium, Thermus aquaticus . The DNA polymerase synthesizes new DNA strands along the template strands, using the primers as starting points. During

12240-475: The producing cell and into their neighbors. Viruses also induce various changes to plants' own intracellular membranes . The work of Perera et al. 2012 in mosquito virus infection and various others studying yeast models of plant viruses find this to be due to changes in homeostasis of the lipids that compose their intracellular membranes, including increasing synthesis . These comparable lipid alterations inform our expectations and research directions for

12360-442: The production of subgenomic RNAs to ensure the translation of all proteins within their genomes. In this process the first protein encoded on the genome, and is the first to be translated, is a replicase . This protein will act on the rest of the genome producing negative strand sub-genomic RNAs then act upon these to form positive strand sub-genomic RNAs that are essentially mRNAs ready for translation. Some viral families, such as

12480-417: The research of potato – potato virus Y interaction is important. Sensitive potato cultivars respond to PVY inoculation with development of typical symptoms. On inoculated leaves 5 – 7 days after inoculation chlorotic and necrotic ringspots develop. As the virus spreads through the plant the systemic symptoms develop on uninoculated leaves. 10 days after inoculation wrinkles and mosaic chlorosis appear, leading to

12600-430: The ribosome will either only produce one protein, as it will terminate translation at the first stop codon , or that a polyprotein will be produced. Plant viruses have had to evolve special techniques to allow the production of viral proteins by plant cells . For translation to occur, eukaryotic mRNAs require a 5' Cap structure. This means that viruses must also have one. This normally consists of 7MeGpppN where N

12720-433: The seed is infected in the generative cells and the virus is maintained in the germ cells and sometimes, but less often, in the seed coat. When the growth and development of plants is delayed because of situations like unfavorable weather, there is an increase in the amount of virus infections in seeds. There does not seem to be a correlation between the location of the seed on the plant and its chances of being infected. Little

12840-404: The solid phase is dependent on temperature, length of exposure as well as concentration. Solid phases used include nitrocellulose membranes, paper, glass, agarose and polystyrene or polyvinylchloride microtiter plates. Microtiter plates are the most widely used solid phase because they are easy to handle, allow for automation and for analysis using microtiter plate readers. A drawback of these plates

12960-411: The solid phase is treated with antibodies raised against the antigen of interest. After each incubation step the plate is washed with Tween 20 containing PBS. These washing steps are aimed to wash away any non-specifically bound components. Nonspecifically bound components are less strongly bound than the specific bound ones. Detection is achieved either through the addition of an enzyme-coupled antibody or

13080-438: The specific domain of the coat protein, and then the insect mouthparts – creating a bridge. In persistent propagative viruses, such as tomato spotted wilt virus (TSWV), there is often a lipid coat surrounding the proteins that is not seen in other classes of plant viruses. In the case of TSWV, 2 viral proteins are expressed in this lipid envelope. It has been proposed that the viruses bind via these proteins and are then taken into

13200-489: The substrate to a coloured product and the colour intensity can be correlated to the amount of antibodies bound and thus the amount of antigen present. A DAS-ELISA has the advantage that it can increase the specificity of the ELISA and reduce the occurrence of non-specific binding. As a result, the DAS-ELISA principle is commonly employed in ELISA's for the detection of plant pathogens in plant sap without prior purification of

13320-415: The tubers are dormant. ELISA detection of viruses in these potatoes is difficult and absorbance values may fall below the set cut-off value. For this reason, seed tuber screening is performed on sprouting rather than dormant tubers. Although this results in more reliable readings than direct tuber testing, it does delay the certification of seed potatoes. Another disadvantage of an immuno-based detection method

13440-432: The use of siRNA in response to dsRNA . Most plant viruses encode a protein to suppress this response. Plants also reduce transport through plasmodesmata in response to injury. The discovery of plant viruses causing disease is often accredited to A. Mayer (1886) working in the Netherlands demonstrated that the sap of mosaic obtained from tobacco leaves developed mosaic symptom when injected in healthy plants. However

13560-471: The virions can be transmitted is limited due to the short period for which they remain infectious. Although the short life span outside plants inhibits long-distance viral transmission, it does not reduce the transmission efficiency bestowed by the quick rate of viral acquisition and inoculation within a field. Upon entrance into the plant cell, the virus coat protein disassembles and releases its RNA genome. The viral RNA serves as mRNA , and although little

13680-559: The virus can replicate, move and infect plants. Understanding the virus genetics and protein functions has been used to explore the potential for commercial use by biotechnology companies. In particular, viral-derived sequences have been used to provide an understanding of novel forms of resistance . The recent boom in technology allowing humans to manipulate plant viruses may provide new strategies for production of value-added proteins in plants. Viruses are so small that they can only be observed under an electron microscope . The structure of

13800-458: The virus entering the foregut of the insect. Those viruses that manage to pass through the gut into the haemolymph and then to the salivary glands are known as persistent. There are two sub-classes of persistent viruses: propagative and circulative. Propagative viruses are able to replicate in both the plant and the insect (and may have originally been insect viruses), whereas circulative can not. Circulative viruses are protected inside aphids by

13920-485: The virus takes place when they become associated with the plant roots. Examples include Polymyxa graminis , which has been shown to transmit plant viral diseases in cereal crops and Polymyxa betae which transmits Beet necrotic yellow vein virus . Plasmodiophorids also create wounds in the plant's root through which other viruses can enter. Plant virus transmission from generation to generation occurs in about 20% of plant viruses. When viruses are transmitted by seeds,

14040-679: The viviparous adults. Nymphs that give rise to winged females may be pinkish. Adult winged aphids have a black head and thorax, and a yellowish green abdomen with a large dark dorsal patch. They measure approximately 1.8 to 2.1 millimetres (0.071 to 0.083 in) in length. The wingless adult aphids are yellowish or greenish in colour, with the possibility of medial and lateral green strips being present. Their cornicles match their body colour, are moderately long and unevenly swollen along their length. The appendages are pale. The adult green peach aphid can be yellowish-green, red, or brown in colour because of morphological differences influenced primarily by

14160-416: The working of the antibodies and is easily detectedusing avidin or streptavidin conjugated to a suitable enzyme. Streptavidin has an extremely high affinity for biotin which results in even a higher degree of specificity than a system in which the enzyme is coupled directly the antigen. To establish whether or not the antigen is present, a substrate specific for the enzyme used is added. The enzyme then converts

14280-534: The yield of root crops and foliage crops. The green peach aphid transmits several destructive viruses in pepper including pepper potyviruses and cucumber mosaic viruses , which causes plants to turn yellow and the leaves to curl downward and inward from the edges. It also is capable of transmitting the Potato leafroll virus (PLRV), which can lead to yield reductions of 40-70%. The green peach aphid can colonize over 100 plant species from 40 diverse families. This

14400-442: Was identified in the 1930s. PVY induces hypersensitive responses in a wide range of potato cultivars. These reactions include the formation of mild mosaic patterns or stipple streak. Unlike the other strains of PVY, some PVY strains are non-aphid transmissible. Previous studies by Visser et al. did not identify any of the local isolates as being PVY but it has been reported to occur in potatoes in South Africa. A second strain of PVY

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