Identification of Damage Symptoms and Control Methods of Tobacco Mosaic Disease

Tobacco mosaic disease occurs commonly in tobacco-growing regions throughout the world, and is found in both northern and southern tobacco regions of China, with the southern tobacco regions suffering more severe damage. It can develop from the seedling stage through to the harvest stage. The incidence rate of affected plants in the field is generally 5-20%, and in individual plots it can reach as high as 90-100%. Losses from early infection can reach 50-70%, or even result in total crop failure. Now let us take a look at the control methods for tobacco mosaic disease!

Damage Symptoms

After a tobacco plant is infected, the lateral veins and branch vein tissues of the young tender leaves become semi-transparent, and the mesophyll tissue on both sides of the veins gradually turns pale green. The virus proliferates massively within the leaf tissue, causing some mesophyll cells to enlarge or increase in number, resulting in uneven leaf thickness and an alternating yellow-green color that presents a mosaic pattern. Later, the mosaic mottling intensifies, and large areas of dark brown necrotic spots appear, especially on the middle and lower old leaves. Severely affected leaves become shrunken, deformed and distorted. Plants infected early have shortened internodes, are severely stunted, grow slowly, cannot flower and set seed normally, and are prone to drop. Capsules that do manage to develop are small and shrunken, with few and small seeds that mostly fail to germinate.

Conditions for Occurrence

Common tobacco mosaic disease occurs mainly from the seedbed stage to the budding stage in the field. Temperature and light greatly influence the spread and epidemic speed of the disease. High temperature and strong light can shorten the incubation period. Continuous cropping or intercropping with Solanaceae crops increases the sources of the virus, significantly raising the incidence rate and severity of the disease. Unsanitary cultivation practices are an important cause of epidemics. Touching back and forth between diseased and healthy plants, applying undecomposed organic fertilizer, and cultivating soil carrying the virus can all aggravate virus transmission. Soil compaction, dry climate, and plots with severe nematode damage in the field show more serious disease occurrence.

Control Methods

1. Select disease-tolerant varieties with strong growth vigor, rapid development and adaptation to local conditions, such as Liaoyan 44, 6315, Guanghuang 54, 176, Nc89, G80, 8611, etc., and pay attention to breeding highly resistant varieties. Implement crop rotation, do not intercrop or relay-crop with Solanaceae plants, and preferably rotate with gramineous crops for 2-3 years. When mosaic disease appears, promptly apply quick-acting fertilizer, earth up and water to promote stem elongation and leaf expansion, thereby reducing the disease.

2. For the seedbed, choose plots where tobacco and Solanaceae plants have not been grown for more than 2 years and that are far from vegetable fields. Use seeds harvested from disease-free plants in disease-free fields, or soak seeds in 0.1% silver nitrate or 0.1-0.2% zinc sulfate or 0.1% trisodium phosphate solution for 10 minutes to remove the virus from the seed surface, and rinse repeatedly after soaking. Before thinning and final singling of seedlings, wash hands thoroughly with soap. When handling, manage healthy seedlings first, and promptly pull out and remove diseased plants when found.

3. Strengthen field management. Strictly prohibit transplanting already-diseased tobacco seedlings into the field. Manage healthy plants first and diseased plants last. Do not smoke during operations, and do not walk back and forth or touch plants repeatedly in the tobacco field. Apply sufficient nitrogen, phosphorus and potassium fertilizer, and promptly spray various trace element fertilizers to improve the disease resistance of the plants. After transplanting, carry out appropriate hardening of seedlings, and irrigate critical water at the late rosette stage to promote plant growth.

4. In the early stage of disease, spray with 2% amino-oligosaccharin 6000-fold solution, or Gaoke 32% moroxydine hydrochloride 800-fold solution, or 1.5% Zhibingling emulsifiable concentrate 1000-fold solution, or 10% Bingduwang wettable powder 600-fold solution, or 3% Huayening wettable powder 300-500-fold solution, which can prevent and alleviate the damage caused by the virus.

5. Aphids play a decisive role in the transmission of common tobacco mosaic disease. On tobacco, they generally reproduce 15-17 generations by parthenogenesis. Therefore, for aphid control, concentrated spraying should be carried out in March to April each year on nearby peach orchards, vegetables and weeds to kill tobacco aphids that have already hatched or are hatching and reviving, thereby achieving the purpose of prevention.

What are the symptoms of tobacco mosaic disease? Control methods for tobacco mosaic disease

Tobacco is one of China's important economic crops, and the occurrence of tobacco mosaic disease seriously affects tobacco yield. So what are the symptoms of tobacco mosaic disease? What are the control methods for tobacco mosaic disease?

Symptoms of Tobacco Mosaic Disease

1. Common mosaic disease: When infected and damaged by the virus, the tender leaves are the first to develop symptoms. The mesophyll along the veins turns yellow, and clear veins appear. Then the dark or light areas gradually expand, forming alternating yellow-green mottling (mosaic). In severe cases, the leaves become uneven in thickness, forming blister-like spots, the leaf margins curl toward the underside, and the leaves become shrunken and distorted, appearing deformed, sometimes with notches or banding. With early infection, plants are severely stunted, with shortened internodes, failure to bush out, and failure to open leaves.

2. Cucumber mosaic disease: When infected and damaged by the virus, the veins are transparent in the early stage of disease, then become mosaic. The leaves become narrower and distorted, the surface hairs fall off, and the leaves lose their luster. Some diseased leaves have margins that curl upward, some show yellow-green or dark green blister-like spots, and some leaves show brown necrosis on the lateral veins, or dark brown lightning-like necrosis along the veins. Plants are markedly stunted, the root system develops poorly, and the upper leaves often show "mosaic scorch spots."

Occurrence Pattern of Tobacco Mosaic Disease

1. Common mosaic disease: This virus can survive for a long time in diseased plant residues. It is mainly mixed in soil, fertilizer, seeds and other diseased residues, as well as in some virus-carrying hosts such as tomato, rapeseed, mustard or perennial weeds. It is transmitted by sap contact, that is, it invades the host through microscopic wounds from mechanical friction, and spreads through vectors such as humans, wind and insects. Plants are susceptible from the seedbed stage to the vigorous growth stage, and resistance increases after topping. A temperature of 18-30°C is most suitable for disease development. Tobacco fields near villages and towns, curing barns, purchasing stations, roadsides, vegetable fields, and fields whose previous crop was tobacco or vegetables show more serious disease occurrence. After transplanting, poor fertilizer and water management, thin, compacted, heavy clay tobacco field soil, poor drainage, and plots where tobacco plants grow poorly show severe disease occurrence.

2. Cucumber mosaic disease: Under natural conditions, this virus cannot survive in dried tobacco leaves. It mainly overwinters in winter vegetables, vegetable seed plants or perennial weeds. In the following spring, it is mainly transmitted and causes damage by tobacco aphids. Therefore, tobacco fields with more weeds, close to cucumber, tomato and other vegetable fields, under high temperature and drought, and when aphid populations are large, show severe disease occurrence. Excessive nitrogen fertilizer application, and barren, compacted, heavy clay soil also lead to more serious disease occurrence.

Control of Tobacco Mosaic Disease

Because tobacco mosaic disease viruses cause mixed infections and have broad transmission routes, control of tobacco mosaic virus must strictly implement the plant protection policy of "prevention first, integrated control," and carry out integrated control measures including agricultural and chemical measures.

(1) Agricultural control measures:

1. Rational crop rotation, adhering to a tobacco-based cropping system

In areas where tobacco mosaic disease occurs frequently, deep plowing of tobacco fields should be carried out during the winter fallow period, exposing the soil to the sun and clearing tobacco stalks, weeds and other plant residues from the field to minimize sources of tobacco mosaic disease. According to actual conditions, rational layout should be arranged, the ecological environment for tobacco leaf growth should be improved and optimized, the industrialization level of tobacco leaf production areas should be raised, and the adjustment of the planting structure in tobacco areas should be accelerated. Do not plant aphid-overwintering host crops of the Solanaceae or Brassicaceae families, such as tomato and pepper, near tobacco fields. Tobacco fields should implement a 1-2 year rotation system as far as possible. In northern tobacco regions of China, wheat-tobacco intercropping may also be appropriately promoted. Combined with soil improvement, planting green manure, returning straw to the field, and field sanitation, rotation can effectively control tobacco mosaic disease.

2. Planting resistant and tolerant varieties

This is the fundamental approach to controlling tobacco mosaic disease that is both economical and effective. Local TMV-resistant varieties include: Liaoyan No. 8, Liaoyan No. 10 and Liaoyan No. 12; Taiyan No. 5 and Taiyan No. 6. Introduced varieties include: Burley 21, Coker 86, Liaoyan No. 15, Yanbian 9205, and CV09-2 from the Tobacco Research Institute of the Chinese Academy of Agricultural Sciences, etc. CMV-resistant varieties include: the TT6 and TT7 series flue-cured tobacco varieties; NC89, K326 and G140 all show a certain degree of resistance. Transgenic NC89 homozygous lines with dual resistance (resistance to both CMV and TMV) have been obtained and tested on a large scale, showing good disease resistance.

3. Strengthen seedbed management and cultivate disease-free strong seedlings.

First, pay attention to seedbed site selection. The seedbed should be as far as possible from vegetable fields, curing barns, drying sheds and similar locations. Second, bed soil and fertilizer must not be mixed with diseased plant residues, and weeds near the seedbed should be cleared. Third, disinfect the nutrient soil of the seedbed to eliminate residual viruses in the seedbed soil. Before sowing in the seedbed, carefully spray the seedbed with agents such as hymexazol and dexon to kill viruses and other pathogens in the bed soil and prevent seedling infection. Fourth, cultivate disease-free strong seedlings. When the tobacco seedlings emerge and reach the cross stage, spray the seedlings with nutrient solution to promote a well-developed root system, so that after transplanting the seedlings recover quickly and have strong disease resistance. Fifth, strengthen seedbed management and strictly follow virus-free operating procedures. Thin and single the seedlings in a timely manner, apply fertilizer and water rationally, and effectively control temperature and humidity. Wash hands with soapy water during operations, strictly prohibit smoking, and minimize contact between operating tools, hands, clothing and tobacco plants.

4. Strengthen field-stage management to improve tobacco's resistance to the natural environment.

Tobacco fields should be deep-plowed and the soil exposed to the sun before winter, and repeated careful harrowing should be carried out to mature the plow layer and reduce sources of infection.

(2) Chemical control measures:

1. Increase fertilizer application to improve plant disease resistance.

Apply organic fertilizer rationally according to the actual conditions of the tobacco field. After tobacco seedlings are planted, spray 1000-fold "Xinxiu" or 1000-fold "Haimoli" tobacco-specific solution. Pay attention to timely topdressing, earthing up and watering to promote a well-developed root system and robust growth of tobacco plants, thereby improving disease resistance.

2. Sanitary operations to reduce virus transmission.

During field operations, first wash hands with soapy water, disinfect tools, and prohibit smoking. Topping and sucker removal should be carried out after rain and dew have dried, and topping and sucker removal on diseased plants should be done last.

3. Pay attention to repelling aphids and preventing them from transmitting the virus.

In seedling beds and tobacco fields, laying silver-gray plastic film or hanging silver-gray reflective film strips can effectively repel aphids from migrating into the tobacco field.

4. Chemical control.

① Spray chemicals to reduce aphid transmission.

Before planting tobacco, aphids on nearby Solanaceae crops and weeds should be killed by spraying to avoid winged aphids migrating and transmitting the virus. Within 40 days after planting tobacco, yellow pan traps should be used to monitor and predict aphids. When winged aphids are found in the pans, spray can be applied immediately in the field for control. In addition, using imidacloprid slow-release granules together with tobacco planting can effectively control the aphid population in the tobacco field and prevent the spread of viral disease in the field.

② Spray antiviral agents.

Spray virus inhibitors (Junkeduke, Bingdubike, etc.) at the seedling stage. Within 7-30 days after transplanting, spray with Bingdubike 600-fold solution and Junkeduke 250-fold solution 2-3 times. When applying, pay attention to spraying both the front and back of the leaves. Within one month after transplanting, apply chemicals 2-3 times to prevent aphids.

In summary, tobacco mosaic disease is transmitted through multiple routes. Therefore, control of tobacco mosaic disease should focus on agricultural preventive measures, combined with effective antiviral agents and rational, sanitary farming operations. Through control methods combining agricultural and chemical measures, create environmental conditions favorable to tobacco leaf growth and unfavorable to the occurrence and development of mosaic disease, effectively control the damage of tobacco mosaic disease to tobacco leaves, and ultimately improve tobacco leaf yield and quality.

Pathogens of Tobacco Mosaic Disease and Excellent Control Tips

It is understood that tobacco mosaic disease damages tobacco leaves. Tobacco mosaic disease causes diseased spots to appear on tobacco plants and affects the normal growth of tobacco.

Generally speaking, tobacco mosaic disease is also called "youtou." After a tobacco plant is infected with tobacco mosaic disease, the tissue between the veins of the tender leaves appears semi-transparent. The mesophyll tissue on both sides of the tobacco veins appears pale green. The tobacco mosaic disease virus proliferates massively within the leaves, causing an increase in the number of tobacco mesophyll cells, and the tobacco leaves appear mosaic-like. As tobacco mosaic disease spreads, large areas of tobacco leaves develop dark brown necrotic spots. When tobacco mosaic disease is relatively severe, the leaves become deformed and shrunken. Tobacco plants infected early become stunted, grow slowly, cannot flower and set seed normally, and are very prone to dropping. Mosaic disease also damages the common strain, tomato strain, yellow spot strain and bead spot strain, among others, and the differences in pathogenicity and mixed infection with other viruses result in diverse symptoms. The pathogen of tobacco mosaic disease is mainly transmitted through sap. Slight friction between diseased and healthy leaves creates microscopic wounds, and the virus can then invade; it does not invade through large wounds or natural openings. Applying undecomposed organic fertilizer among tobacco plants and cultivating soil carrying the virus can both aggravate transmission of the tobacco mosaic disease virus.

In order to control tobacco mosaic disease in a timely manner, effective measures should be taken for prevention and control. Agricultural workers should strengthen management among tobacco plants and select tobacco varieties with strong disease resistance and good quality for sowing. Deep plowing and renewing the soil in tobacco planting areas is more conducive to the later growth and development of tobacco. After discovering diseased tobacco plants, agricultural workers should promptly pull them out, take them away from the planting area for destruction, and spread quicklime in the area of the diseased plants, which can effectively prevent the spread of tobacco mosaic disease. Strengthen management during the tobacco seedling stage, select disease-free plants for seed harvesting, or soak seeds in 0.1% silver nitrate or 0.1%-0.2% zinc sulfate or 0.1% trisodium phosphate solution for 10 minutes, and rinse repeatedly after soaking. In the early stage of tobacco mosaic disease, spray with 2% amino-oligosaccharin 6000-fold solution, or Gaoke 32% moroxydine hydrochloride 800-fold solution, or 1.5% Zhibingling emulsifiable concentrate 1000-fold solution, or 10% Bingduwang wettable powder 600-fold solution, or 3% Huayening wettable powder 300-500-fold solution, which can prevent and alleviate the effects of the tobacco mosaic disease virus.