Tomato Spotted Wilt Virus Disease in Tobacco
TSWV (Tomato spotted wilt tospovirus)
TSWV is formed in the form of concentric circles, annular wounds and spots in the tissues of young leaves. The first stain is yellow green and the area that dies later turns red-brown. Concentric rings, white-rim necrotic area, necrotic white spots, white-colored necrotic lines in the form of ferns or oak leaves around the main or lateral veins are seen as leaf signs of the disease. The disease shows its most serious damage after the peak necrosis caused by systemic infection. As a result of the crown and stem necrosis, the diseased plant curves to that side, the leaves become deformed.
In the early period (seedbed) or immediately after planting, the tobacco dwarf and leaves itself as if it is broken or bends. As seen in the seedling and seedling photos below, young leaves become infected from the middle and lateral veins and shrink, showing uneven growth. Seriously caught tobaccos cannot thrive and fall off after a few weeks. Necrotic spots occur around the leaf veins on old leaves. Symptoms can vary between hosts or even within the same plant.
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Disease Contagion to Tobacco
The disease is transmitted by thrips, which are vector insects. Annual thrips populations with the presence and movement of host plants are effective in the transport and spread of the disease. Thrips larvae feed on the diseased plant and absorb the virus in the plant sap. The larva that receives the virus continues to infect the virus also in the adult period. Adult thrips virus cannot be received. Infection occurs only by thirips that feed on the diseased plant during the larval stage. Adult thirips that do not feed on the diseased plant during the larval stage cannot transmit disease. Infection occurs during thrips feeding in epidermis cells. If the temperature is 25 ° C for 5 days, the disease symptoms can be seen in 3 weeks at 10-12 ° C. There are different races of the virus.
TSWV is seen in weeds, ornamental plants and cultivated plants such as tomatoes, peppers and lettuce, and causes economic damage in many field and garden products. In the regions where there is a very dense thrips population, 80-95% of the disease and 10-40% for the medium and weak populations have been determined in the studies. The virus is refreshed by the transmission of vector insects and lives continuously. It does not pass directly with thrips eggs. The fact that the disease is seen in the newly planted tobacco even though there are no thrips in the field indicates that the plant got the disease in the seedling period. This misleads the manufacturers.
As a feature of the virus disease, at high temperatures, 32 degrees and above, the disease enters the sleep cycle and does not show symptoms. Some sources state that "in general, the virus becomes inactive at high temperatures and the overhead parts disappear, while the parts in the root are active". If infected tobaccos can find water in the latent circuit, it comes to life and shows a second growth. During this growth period, 8-10 more leaves grow on the diseased leaves. Although some of the newly emerged leaves show signs of disease, they are obtained from qualified leaves without signs of disease. It is also reported that TSWV-infected tobacco grows by cutting from 15-20 cm above the ground. Since the second growth or post-mowing growth depends on the seasonal temperature-rainfall, crushing and drying works may be left to September-October. Loss of productivity is tried to be prevented with these procedures performed during the sick years.
Life Circuit of the Vector
Thrips are a small, cylindrical waste insect. They spread by jumping or flying. Adults and pupae spend the winter on plants or their residues. It is 1 mm long, yellowish and dotted at the end. Females constantly reproduce without males. It is a polyphagous insect. It absorbs the leaf tissue by biting. Lays white, bean-shaped eggs on leaf tissue or stem. After 5-10 days, the larvae hatch from the eggs. It gives 3-5 generations a year. A female lays an average of 30 eggs. Especially in the field period, more than 400 thrips per plant can be found in tobacco that is late in the fight.
Fight in Tobacco
The lack of a drug fight against the virus disease makes protective struggles important. What can be done under these conditions are as follows:
• Since the virus can be transported in the seed coat, certified seeds should be used, and seeds should not be taken from diseased plants.
• Weed control should be done in and around the seedbed,
• There should not be plants such as tomatoes, peppers, and onions in and near the seedbeds,
• Thrips struggle should be done in the seedbed, if necessary, periodic struggle should be started. Seedling applications should be done when the seedling leaves are dry. Some of the infections occur in nurseries. At low temperatures, the symptoms of the disease appear in the field after planting and the struggle becomes difficult. Thrips struggle in the seedbed is both very easy and very cheap . Systemic drugs should be used in the seedbed and field periods.
• Thrips can be spread over vast areas by the wind and are ubiquitous. Thrips population should be monitored in planted fields. The struggle in the field circuit is both difficult and expensive .
• Second spraying should be done at 7-10 days intervals on the planted field. It is important that all manufacturers make this fight in order to prevent the spread of thrips and therefore the virus disease.
• Spring rains in April-May reduce the thrips population in tobacco, making the fight easier.
• Many tobacco producers do not believe that this disease is transmitted by thrips and attribute this to other causes. When the cause of the disease is unknown, success cannot be achieved in the fight. The producers should be educated and the transmission and spread of this disease should be explained.
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Result
There is no medicated fight against TSWV disease in tobacco. Thrisps, which are vector insects, should be dealt with without waiting for the economic damage threshold. It is transmitted by thrips that feed as larvae on winter weeds that host the virus. The fact that the disease has a lot of hosts makes the struggle difficult. During the mild winters, the thrips wintering, entering the spring strongly, spreading the disease and not being able to do collective struggle are among the difficulties of the struggle.
Drying Tobaccos with TSWV
