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Pest: Tobacco Mosaic Virus (TMV)

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Pest: Tobacco Mosaic Virus (TMV)

 

 

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Warning:

 

Tobacco mosaic virus (TMV) can also be carried in cigarettes and rolling tobacco. There is NO cure.

 

 

Special Species Notes

 

TMV origins in the Americas.

 

TMV is known as one of the most stable viruses. It can even survive through various harsh conditions. Some of these conditions include infected plant material that is rotting away in the garden, soil that has contaminants as well as the most common, tobacco products. It can live as long as 30-50 years.

 

TMV is a virus belonging to the Potyviridae family that consists of small rods approximately 700 nanometres long. It's a positive-sense single stranded RNA virus that infects a wide range of plants, especially tobacco and other members of the family Solanaceae (nightshades). The infection causes characteristic patterns, such as "mosaic"-like mottling and discoloration on the leaves (hence the name).

 

TMV was the first virus ever to be discovered. In 1886, Adolf Mayer first described the tobacco mosaic disease that could be transferred between plants, similar to bacterial infections.  In 1892, Dmitri Ivanovsky gave the first concrete evidence for the existence of a non-bacterial infectious agent, showing that infected sap remained infectious even after filtering. Although it was known from the late 19th century that an infectious disease was damaging tobacco crops, it was not until 1930 that the infectious agent was identified as a virus. Tobacco mosaic virus was the first virus to be crystallized. It was achieved by Wendell Meredith Stanley in 1935 who also showed that TMV remains active even after crystallization.

 

TMV has a very wide survival range. TMV is a thermostable virus. As long as the surrounding temperature remains below approximately 40 Celsius (104F),  TMV can sustain its stable form.  On a dried leaf, it can withstand up to 120 degrees Fahrenheit (50 °C) for 30 minutes.  All it needs is a host to infect. If necessary, greenhouses and botanical gardens would provide the most favorable condition for TMV to spread out, due to the high population density of possible hosts and the constant temperature throughout the year.

 

aphids, which happen to be common Cannabis pests, are not carriers of TMV however others are.

 

Identification

 

Tobacco mosaic virus has a rod-like appearance. Its capsid is made from 2130 molecules of coat protein and one molecule of genomic single strand RNA, 6400 bases long. The coat protein self-assembles into the rod-like helical structure (16.3 proteins per helix turn) around the RNA which forms a hairpin loop structure.

 

 

Host plants:

 

TMV has a very wide host range and has different effects depending on the host being infected. It isn’t very selective, but it does have a high impact. A plant infected with TMV will never recover its previous strength because of state of the leaves, photosynthesis will remain reduced. The plant will never be a great one. TMV rarely kills the plant.  It is known to infect members of nine plant families, and can infect well over 350 different species of plants, including tomato, pepper, cucumber, petunia, eggplant, tobacco, spinach, cannabis, and a number of ornamental flowers such as marigold.

 

Losses of 20-80% were common on plants infected with TMV, and for fresh market crops such as tomato and pepper, the fruits were often distorted or blemished which further reduced the wholesale and retail value.

 

 

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First signs:

 

Symptoms vary with the species of plant infected and the environmental conditions. In some cases environmental conditions bring out symptoms while other conditions mask  symptoms. Symptoms associated with TMV infections:

 

Leaf Color:

 

Brown, burnt edges
 

Pale color
 

Yellowing of new growth
 

Yellowing of lower, older leaves
 

Yellowing between veins or a distinct yellowing only of veins

 

Yellow streaking and/or spotting
 

Dark or purple in color
 

Black or gray patches
 

White powdery patches

 

Brown, dark spots
 

Mottling, mosaic pattern of light and dark green (or yellow and green)

 

A light green coloration between the veins of young leaves. This is followed quickly by the development of a "mosaic" or mottled pattern of light and dark green areas in the leaves. Rugosity may also be seen where the infected plant leaves display small localized random wrinkles. These symptoms develop quickly and are more pronounced on younger leaves. Lower leaves are subjected to "mosaic burn" especially during periods of hot and dry weather. In these cases, large dead areas develop in the leaves. This is one of the most destructive phases of TMV infection. The infected leaves may be crinkled, puckered, or elongated. However, if TMV infects crops like grape and apple, it is almost symptomless.

 

You'll be able see the tobacco mosaic virus by its green mottled areas on the leaves. These mottled areas are both dark and light green and are caused by the presence of the virus. Oftentimes the dark parts of the leaf are physically thicker than the lighter parts. Additionally, if the leaf is underneath shade than it is easier for a person to spot the discoloration.

 

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Tobacco plant with TMV showing mottled leaves

 

Leaf Symptoms:

 

Upper, newer growth affected
 

Lower, older growth affected; curl from the tips downwards.
and slightly distorted

 

Burnt leaf edges and tips
 

Death of leaf tips
 

Yellowing between veins
 

White powdery patches
 

Red stems
 

Spots
 

Mottling, mosaic pattern
 

Old leaves fall off
 

Slowed growth
 

Twisted, abnormal growth
 

Leaves curling under or upwards
 

Wilting, drooping
 

malformation/distortion of leaves or growing points. Fern-like appearance of leaves

 

 

 

 

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squash plant that has caught Mosaic Virus

 

Plant Symptoms:

 

Red or purple stems
 

Weakened stems
 

Old leaves falling off
 

Slowed growth
 

Twisted, abnormal growth
 

Wilting or drooping
 

Slowed root growth

 

Stunted: Tobacco Mosaic Virus causes stunted growth in young plants, and may distort the leaves into a fern-like shape. Stunting is very common especially in new and young plants. It is caused by the plant’s inability to efficiently process UV light.

 

Depending on the virus strain, buds might also be mottled, streaked, or show signs of necrosis. While this necrosis does not destroy the plant completely, it causes the buds to be very weak and of low quality.

 

While plants that are affected won’t be killed by the virus, they will have small low quality buds and, therefore, worse yields.

 

Some of the above symptoms (stunting, mosaic pattern of the leaves, yellow spots or streaks) can also be caused by high temperature, insect feeding, growth regulators, herbicides, mineral deficiencies, and mineral excesses. TMV diseases cannot be diagnosed on the basis of symptoms alone. There are test kits you can buy to confirm TMV.

 

 

Life cycle

 

TMV does not have a distinct overwintering structure. Rather, it will over-winter in infected tobacco stalks and leaves in the soil, on the surface of contaminated seed, TMV can even survive in contaminated tobacco products for many years. With the direct contact with host plants through its vectors (normally insects are leaf chewers like the grasshopper or leafhoppers), TMV will go through the infection process and then the replication process. After its multiplication, it enters the neighboring cells through plasmodesmata. The infection spreads by direct contact to the neighboring cells.

 

TMV can be transmitted from one plant to another by direct contact. Although TMV does not have defined transmission vectors, the virus can be easily transmitted from the infected hosts to the healthy plants, by human handling. Explained in the section below

 

 

 

How it spreads:

 

An attack by mosaic virus occurs mainly in summer and autumn.

 

TMV can be your hands, clothing or on tools. This is called 'mechanical' transmission. When plants are handled, the tiny leaf hairs and some of the outer cells inevitably are damaged slightly and leak sap onto tools, hands, and clothing. If the sap contains TMV, it can be introduced into other plants when those come in contact with this sap. Sucking insects such as aphids do not spread TMV. Chewing insects such as grasshoppers and caterpillars occasionally spread the virus but are usually not important in spread.

 

It can live in contaminated soil, infected plant debris, the coating of a seed, and even in tobacco products that have been manufactured. The virus travels between plants generally through a mechanical cause.

 

TMV can also survive outside the plant in sap that has dried on tools and other surfaces. If a TMV plant is handled and then you open a door with that hand, you have now put TMV on the door handle. The next person to open the door can pick up the TMV and spread it to any plant that they touch.

 

Unfortunately, once your plants are infected with a virus, there is not much you can do about it. Virus diseases simply can’t be controlled once they have been infected. This is why it is particularly important to prevent the virus from infecting your plants in the first place.

 

 

What to do for preventative use

 

Your best weapons against the transmitting of this disease are sanitation and caution.

 

Start your grow with a clean space, so make sure it has as few bugs as possible and wash your hands before playing with your plants.  If this virus gets in the mother plant, then there’s a 99% chance that you’ll get it in your grow space too.

 

 The environmental factors are important; a plant in a constant environmental temperature of 21 degrees Celsius (69.8F) or higher will have less trouble from the virus, so keeping your temperature up at this level is essential.

 

One of the common control methods for TMV is sanitation, which includes removing infected plants, and washing hands in between each planting. Crop rotation should also be employed to avoid infected soil/seed beds for at least two years. As for any plant disease, looking for resistant strains against TMV may also be advised

 

Remove all weeds since these may harbor TMV. Remove all crop debris from benches and the greenhouse structure.

 

If you do discover a plant that has been infected, or if you are unsure whether your plant has TMV, place it in quarantine while running other tests like flushing out the soil and cleaning the foliage. You can buy testing kit to obtain a diagnosis.  If your plant does not recover and/or its been confirmed that the plant has TMV, dispose of it immediately.  If caught early enough, this should stop the spread of the tobacco mosaic virus.  There is no real solution since once it’s in the plant it cannot be cured. The virus particles are found in all parts of the plant except the few cells at the tips of the growing points. An infected plant should be discarded immediately.

 

Disinfest tools by placing them in disinfectant for at least 10 min. Rinse thoroughly with tap water.

 

Disinfest door handles and other greenhouse structures that may have become contaminated by wiping thoroughly with one of these materials.

 

Thoroughly wash hands after handling tobacco products or TMV-infected plants. Wash your hands with soap and hot water. This will prevent TMV from spreading to any other plants you are handling.

 

 

 

 

 

 

 

 

The link below will take you to "An Intro to beneficial bugs and beneficial insect food" it has a list (been worked on) to pests and beneficial insects

 

 

  http://freemygreenpdx.com/topic/14334-an-intro-to-beneficial-bugs-their-food-and-the-pest-they-take-care-of/

 

 


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