Viruses in Potatoes

Potato Virus Y

Potato virus Y , 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 symptoms is causing production loss, the most serious is called 'potato tuber necrotic ringspot disease' (PTNRD) which is transmitted by aphid vectors.

[Image from: http://vegetablemdonline.ppath.cornell.edu/NewsArticles/Potato_Virus.htm ]

Potato leafroll virus

Potato leafroll virus infects potato and is a particular problem in the USA. During the summer, the virus is spread by insects and by the green peach aphid, Myzus persicae. During the winter months the viruses lie dormant in the plants and are the primary source of new infections of other plants in the next year. The symptoms of this disease include a slight curling of new leaves and the leaves become discolored, ranging from a light green through yellow to red and the underside of the leaves turns purple. The disease will reduced the yields and quality of the potato crops but not killing plant.

[Image from: http://vegetablemdonline.ppath.cornell.edu/NewsArticles/Potato_Virus.htm ]

Potato mop top virus

The Potato mop top virus (PMTV) is a pomovirus vectored by the fungus Spongospora subterrenea, which causes powdery scab of potato. The virus can be found in scab spore-balls and can remain viable in the field up to 18 years without the host. Symptoms of PMTV vary depending on environmental conditions. The symptoms may include yellow rings, V shape markings, and blotches, especially on the lower leaves. Stems may also be stunted, giving a “mop top” effect.

[Image from: http://vegetablemdonline.ppath.cornell.edu/NewsArticles/Potato_Virus.htm ]

Tobacco rattle virus

Tobacco rattle virus (TRV) is a Tobravirus which causes corky ringspot or spraing disease. Often found in sandy soils. Symptoms often do not appear on the foliage, but the tuber contains corky layers of tissue interspersed with rings of healthy tissue and brown flecks distributed throughout the tuber. This virus is transmitted by 'stubby-root' nematodes .

[Image from: http://vegetablemdonline.ppath.cornell.edu/NewsArticles/Potato_Virus.htm ]

Transmission of Plant Viruses

Transmission

• Sap
• Insects
• Nematodes

Sap

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.



Insects

Plant viruses need to be transmitted by a vector, most often insects such as leafhoppers. The chosen insect vector of a plant virus will often be the determining factor in that virus's host range. Plant virus are classified as non-persistent, semi-persistent and persiste depending on the different ways of transmission by insects.

Green peach aphid Myzus persicae, the vector of many plant viruses, including Potato virus Y.

[Image from: http://www.dpvweb.net/intro/index.php#transmit ]

Hoppers transmit viruses from several genera.

Micrutalis malleifera, the treehopper vector of Tomato pseudo-curly top virus.

[Image from: http://www.dpvweb.net/intro/index.php#transmit ]

 Nematodes

Soil-borne nematodes also have been shown to transmit viruses. They acquire and transmit them by feeding on infected roots. The virions attach to the stylet or to the gut when they feed on an infected plant and can then unattach during later feeding to infect other plants. Example of viruses that can be transmitted by nematodes includes tobacco rattle virus.

Adult female of Paratrichodorus pachydermus, the vector of Tobacco rattle virus.

[Image from: http://www.dpvweb.net/intro/index.php#transmit ]

Plant Viral Structures

Virus Shapes

Viruses are extremely small and can only be observed with an electron microscope.


Over 50% of known plant viruses are rod-shaped. The second most common structure amongst plant viruses are isometric particles.


Tobacco mosaic virus, the length is about 300-500 nm with a diameter 15-20 nm.

(image from: www.apsnet.org/.../TMV/text/fig06.htm )

Tobacco necrosis virus A, diameter varies from 40-50 nm in diameter

[Image from: www.ncbi.nlm.nih.gov/.../00.074.0.03.001.htm]

Cocoa swollen shoot virus, genus Badnavirus [largest size is 30 nm wide and 300 nm long]

[Image from: www.dpvweb.net/intro/index.php ]

Link: http://www.dpvweb.net/intro/index.php

Viruses in Plants

Plant Viruses

Plant viruses are viruses affecting plants. They are less well known than bacteril and animal viruses, even though viruses were originally identified and isolated from tobacco plants. Plant viruses infect many food crops, including corn, beans, tobacco and the most popular in the world, potatoes, viruses resulting billions of dollars in losses each year. Viruses of plants are introduced into plant cells either through abrasions of the cell wall or by plant parasites such as nematodes and aphids.

The first virus to be discovered was Tobacco mosaic virus (TMV). This and other viruses cause an estimated US$60 billion loss in crop yields worldwide each year. The TMV viruses are most frequently used as research in plant molecular biology today.


There are over 2000 known viruses and about 1/4 of these known viruses cause diseases in plants. Plant viruses are grouped into 73 genera and 49 families.

Viruses in Plots

Viruses have fascinated and frightened us all. That ability has made them popular in creating science fiction for novels and movies. Such notable examples are listed here.


Movies:

1) "Outbreak" - click here to read interview with Dr. Murphy






Novels:

Title Medusa : A novel from the NUMA files / Clive Cussler ; with Paul Kemprecos.


Author:      Cussler, Clive.

Summary:  Kurt Austin puts the NUMAA team on a case involving a hideous series of medical experiments, an extraordinarily ambitious Chinese criminal organization, and a secret new virus that threatens to set off a worldwide pandemic.
 
[From: http://catalogue.nlb.gov.sg]

Viral Scoop

Viral Scoop I


“There is good circumstantial evidence that the specific origin of placental mammals is the result of an ancestral species being infected with an immunosuppressive proto-retrovirus. It is suggested that this immunosuppression permitted an immunological accommodation in the mother to the development of a genetically distinct individual in the placenta during a prolonged gestation!”

– pg 9, Basic Virology, Edward K. Wagner, Martinez J. Hewlett, David C. Bloom, and David Camerini

Viral Diseases in Honey Bees

Honey Bees

"Honeybee hives have long provided humans with honey and beeswax. Such commercial uses have spawned a large beekeeping industry, though many species still occur in the wild."

[Image from :http://animals.nationalgeographic.com/animals/bugs/honeybee.html ]

Learn more about them at http://animals.nationalgeographic.com/animals/bugs/honeybee.html





Diseases

There are four diseases listed here:

• Sacbrood
• Chronic Bee Paralysis
• Black Queen Cell Virus
• Deformed Wing Virus
  
  
  

Sacbrood

Symptoms of sacbrood include partially uncapped cells scattered about the frame or capped cells that remain sealed after others have emerged. Diseased individuals inside cells will have darkened heads that curl upward, resembling a slipper inside the cell. The diseased prepupae fails to pupate and turns from pearl white to pale yellow to light brown and finally, dark brown. The skin is flaccid and the body watery. The dark brown individual becomes a wrinkled, brittle scale that is easily removed from the cells.


Researches estimate that one larva killed by the sacbrood virus contains enough virus to kill over one million larvae.

The viral infection process in not known as well what triggers the infection or how it persists.



Chronic Bee Paralysis

(Hairless black syndrome)

These viral infection symptoms appear only in adult bees.

They are

• trembling motion of wings and body
• unable to fly, tend to resort to crawling up to hive
• bloated abdomen and partially spread or dislocated wings 
• lack of hair causes shiny and greasy appearance

Lack of hair causes bees to be confused with robbing bees. Some mistaken infected bees are chewed by other bees and haressed by guard bees. Within a few days of the onset of symptoms, the adult bees dies.

The virus is spread from bee to bee by direct body contact. Food exchange does not appear to be an important mode of spread. Bees vary genetically in susceptibility; therefore requeening is a good practice if symptoms appear.

[Image from: http://www.ent.uga.edu/Bees/disorders/viral-diseases.html#blackqueen]

Black Queen Cell Virus

As the name suggests, the virus infects the queen larvae. The immature larvae dies and turns black after its cell is sealed.

The departure of the queen larvae could be serious if the infection were to spread to all the queen larvae.

There may be an association between Black queen cell virus and Nosema disease. Treating colonies with Fumidil-B® to control Nosema may help keep this disease at bay.

Deformed Wing Virus (DWV)

Parasitic Varroa mites are suspected to be associated with the spread of DWV or in its activation.

The bee pupae at white-eyed stage is susceptible to this virus. The virus multiplies slowly in the infected bee allowing it to reach adulthood. The adult bees have misshapened wings and soon die.

The best management against DWV is aimed at parasitic Varroa mites.

[Image from: http://www.ent.uga.edu/Bees/disorders/viral-diseases.html ]

[From: http://www.ent.uga.edu/Bees/disorders/viral-diseases.html ]