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Potato (Solanum tuberosum subsp. tuberosum) is one of the world's major staple food crops, after rice, wheat, and maize. It can be eaten fresh or processed into a variety of products such as potato chips and mashed potatoes. Potato is an asexually reproducing crop and is therefore susceptible to viruses, of which Potato virus Y (PVY) is currently recognized as the most important viral pathogen with a global distribution.
PVY is a type member of the genus Potyvirus in the family Potyviridae comprising viruses with a single-stranded, positive-sense RNA genome of approximately 9.7 kb.
There is a poly (A) tail at the third end of the PVY genome and a covalently linked VPg protein at the fifth terminal, both of which are involved in genome protection, genome replication and genome expression regulation. The PVY genome synthesizes and expresses a single large polyprotein, which is then cleaved into 10 mature proteins by three virus-specific proteases. The C-terminal fragment of the polyprotein encodes a single phage protein (CP) of 267 amino acids (aa), which can wrap the virus RNA and form helical slender particles about 740nm in length and 11nm in diameter. An additional protein is produced from an overlapping ORF after +2 frame shifting of the P3 cistron, as fusion to the amino (N)-terminal part of P3 (P3N-PIPO). HC-Pro is involved in aphid transmission, virus multiplication, intercellular and systemic movements, and symptom intensity. The protein, P3 contains two hydrophobic structural domains, located at the N-terminal and C-terminal ends, which are involved in viral replication, systemic infection, pathogenicity, and movement. The CI protein forms the laminate cytoplasmic inclusion bodies (pinwheel-shaped), typical of potyviral infections. Its involvement in cell-to-cell virus movement is well established whereas the RNA-binding, RNA helicase and ATPase activities strongly suggest an important role in virus replication.
PVY exists as a complex of strains, strain groups, or variants. Since the late 1980s, with the development of genome sequencing capabilities and advances in molecular plant virology, a large number of PVYs have been sequenced and molecularly characterized. It is known that PVYs differently recombined from PVYO and PVYN sequence fragments.
Figure 1. The main types of PVY recombinant genomes found in nature
(Source: Karasev AV, et al. 2013)
PVY is spread from plant to plant by aphids, mechanical means or by contact:
There are currently more than 50 species of aphids capable of transmitting PVY with varying degrees of efficiency. Aphids transmit PVY in a non-persistent manner, with acquisition and inoculation occurring in less than a minute, giving many species of aphids ample opportunity to transmit the virus. Once a plant's leaves are inoculated with aphids, the virus is transferred to the tubers, with the efficiency of transfer varying by species. The Myzus persicae is clearly the most important vector in most areas and seasons of the potato crop because of its wide distribution and high transmission efficiency, with the virus being able to remain in its body for up to 4 hours.
Disturbance by wind or human activity between infected plants and neighboring healthy plants can lead to mechanical spread of PVY. Infected plant wounds secrete fluids containing viruses, and when in contact with nearby healthy plants, the wounds of healthy plants may be exposed to some of the viruses. Mechanical cutting operations likewise carry the risk of spreading PVY.
The degree of development of symptoms depends on the interaction between viral proteins and the molecular mechanism of host plants, the expression level of viral genes using host plant proteins, and the spread of newly formed virus particles throughout the plant.
On potato it shows, mild to severe leaf mosaic, or streak or 'leaf-drop streak' (leaves either fall from the plant or remain suspended, often giving a bare stem with leaves at the tip) with vein necrosis or 'stipple-streak'.
Primary infection with necrotic strains usually causes necrotic rings or necrotic spots and mild to very mild mottling later in the season. Secondary symptoms are usually more pronounced early in the season and manifest as severe mottling. Some strains of necrotrophic fungi cause a destructive disease on tubers called potato tuber necrotic ring disease. Infection with common strains causes leaflet necrosis, mottling or yellowing, defoliation, and death.
Figure 2. Symptoms induced by PVY
(Source: Quenouille J, et al. 2013)
Estimating the economic losses of potatoes due to PVY is complicated by a number of factors. For example, in the case of mixed infections with other viruses, PVY can cause more severe symptoms. In addition, the time of infection can affect the severity of the disease. Seedlings are more susceptible and symptomatic when infected early in the season, and the greatest losses have been reported when crops are planted from infected seed tubers, with yield losses of 30%-64%.
One study found that for every 1% PVY added to seed, yields were reduced by 0.18 t/ha, and would reduce marketable yield and tuber size. An economic assessment estimated losses of US$34 million (direct and indirect production costs) in Idaho, USA, which produces about 7.1 million tons of potatoes annually, valued at US$1 billion. It is estimated that 10% PVY infection in seed can reduce yields by $90-120 per acre, depending on the market sector.
Resistance to PVY in potato may be conferred by two different types of resistance genes: Extreme resistance (ER) or immunity is conferred by R genes, and HR is conferred by N genes. HR is defined as limited replication of the virus resulting in visible localized necrotic lesions in the inoculated leaves, thereby limiting the transfer of the virus to other plant tissues or resulting in a systemic necrotic response throughout the plant. Both ER and HR can be used to control virus spread in potato, with HR being sensitive to environmental conditions and more easily broken down.
Genetic improvement of PVY resistance in potato is essential for sustainable potato production. Conventional breeding to integrate major resistance genes is still an effective way to develop new varieties, but conventional techniques are time-consuming and labor-intensive due to the extremely high heterozygosity and complex genetics of potato.
Another well-established method for modifying PVY resistance is transgenic technology. Transgenic potato plants overexpressing PVY-derived coat proteins, PVY-specific dsRNAs (for RNAi), or the modified plant eIF4E have shown high levels of resistance, but commercial development of this category has been limited by regulations and negative public perception of transgenic plants.
Nowadays, CRISPR/Cas (clustered regularly interspaced short palindromic repeats/CRISPR-associated genes) and spray-induced gene silencing (SIGS) provide a new and less controversial way to improve PVY resistance. The CRISPR/Cas system generates plant virus resistance either by directly suppressing viral DNA/RNA or by introducing mutations into "susceptibility" genes in the host plant. Both approaches have been successfully used to improve potato resistance to PVY. For example, researchers have engineered resistance directly against the PVY P3, CI, NIb and CP genes in transgenic potatoes expressing Cas13 and gene-specific sgRNAs. CRISPR/Cas9 tools have also been used to generate PVY resistance by positional mutagenesis of the potato colin gene. Spray-induced gene silencing (SIGS), another RNAi-based genomic technology for targeting various pests and pathogens, including viruses, has been successful in inducing resistance to different viruses in a wide range of crops by spraying plants with exogenous dsRNAs. The SIGS technology for disease control appears to be potentially sustainable and environmentally friendly and could be used to protect potatoes from PVY.
References
| Target | Cat. No. | Product Name | Size | Species | Application | Detection Sample | |
| PVY | DEIAPV6 | Potato Virus Y (PVY) ELISA Kit | 500T/1000T/5000T | Qualitative | Host plants | Inquiry | |
| DEIAPV236 | Potato virus Y-necrotic strain (PVY-n) ELISA Kit | 500T/1000T/5000T | Qualitative | Host plants | Inquiry |
| Target | Cat. No. | Product Name | Host | Isotype | Application | |
| PVY | CABT-BL6168 | Anti-PVY polyclonal antibody | Rabbit | IgG | ELISA, LFIA | Inquiry |
| CABT-BL6264 | Anti-PVY polyclonal antibody [AP] | Rabbit | ELISA, LFIA | Inquiry |
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