Wild Fever Disease in Tobacco
Pseudomonas syringae pv. tabaci is a 0.5-0.75x1.4-8.0 µm in size, unencapsulated, 1-6 polar flagella, aerobic and Gram-negative bacterium. The agent produces a toxin called tabtoxin. Tabtoxin forms yellow lesions on tobacco leaves without bacteria. The optimum growth temperature of the agent is 22-25°C, the minimum temperature is 0°C and the maximum temperature is 35°C.
The agent can overwinter in plant residues in the soil, dried or dried diseased tobacco leaves, seeds in infected seed pods, seedbed covers, and the roots of some weeds or crop plants. Bacteria carried to the leaves by raindrops and wind from these contamination sources initiate primary infections by entering through large stomata, hydatids (stoma-like structures that allow excess water to be thrown out in plants) or wounds opened by insects and other factors. Bacteria continue to spread between cells and produce the first symptoms on leaves. They also produce tabtoxin at points of infection.
Especially humid climatic conditions encourage the development of the disease. In humid weather, bacteria spread more easily between cells and cause death in parenchyma cells through the toxins and enzymes they secrete. In these conditions, the dead parts are easily separated from the healthy tissues and fall to the ground or secondary infections occur when they reach other plants with the air flow.
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The disease agent usually produces its first symptoms on the leaves of young plants in the seedling, but it can affect plants of any age. It manifests itself in the form of wet rot or areas that look like boiled in water, especially on the edges and ends of the leaves of underdeveloped tobacco seedlings. The whole leaf or part of it may rot and fall. While some of the infected seedlings die in the nursery, some may die after being transplanted into the field.
Typical manifestations of the disease are round, yellowish green spots 0.5-1.0 cm in diameter on the leaves of field plants. Within 1-2 days the center of the spots turns brown and is surrounded by a yellowish green halo. As the disease progresses, the spot centers and the surrounding halo expand and within a few days the brown spot centers reach 2-3 cm in diameter. Spots close to each other may coalesce to form irregular, large dead areas. In dry weather these diseased areas dry up and stay in place, while in humid weather they fall off. Spots can also be seen rarely on flowers, seed capsules, petioles and stems.
Wildfire causes significant losses in seedlings in humid climatic conditions. Infections in the field period, on the other hand, significantly reduce the leaf quality as well as the quantity. The disease is common in most tobacco and soybean producing countries around the world. In our country, it is seen in the Black Sea and Marmara Regions, and rarely in the Aegean Region.
P. syringae pv. The most important hosts of tabaci are tobacco (Nicotiana spp.) and soybean (Glycine max). However, the agent can infect a wide variety of plants and can be found on the root surface of many plant species.
Cultural Measures
- Since the disease is transmitted by seeds, seeds should not be taken from the production areas where the disease is seen, disease-free seeds and seedlings should be used in production.
-Seedling soil and covers should be sterilized with disinfectants or steam before planting.
Nitrogen fertilizer should not be used in the nursery or in the field, which ensures rapid growth, especially more than necessary.
- If a disease is observed in the seedling, the diseased seedlings should be removed and destroyed immediately. In order to create a safety strip between diseased and healthy seedlings, all plants at a distance of 25 cm should be removed and the resulting empty space should be disinfected with formaldehyde.
-Only healthy seedlings should be transplanted into the field, and in case of disease in the field, infected plants should be immediately removed from the production area and destroyed.
Drug control against wild fever in tobacco is carried out in the form of seed and seedling spraying. Seed spraying should be done before planting, and seedling spraying should be done as 2-3 applications at 8-10 day intervals after the seeds germinate and cover the soil surface.
Back sprayer (mechanical, automatic, motorized) is used in seedling spraying.
Seed spraying, which has a protective nature, is done by dipping the seeds in a cloth bag into a 40% formalin solution for 15 minutes before planting. The seeds sprayed in this way are thoroughly rinsed with water, dried and then planted. Seedling spraying should be done in the form of coating, early in the morning.
*Ministry of Agriculture, Agricultural Protection Technical Instructions Vol:2
