Symptoms can develop throughout the reproductive period. Under natural conditions, the incidence of seedlings is small or there are few symptoms. The disease usually begins in 3-5 true leaf stages. After the middle and late stages of cotton budding, a large amount of disease develops in the fields. At the beginning, light yellow patches appear between the leaf margins and the land veins on the lower leaves of the plants, and then gradually expand, and the leaves lose color. Shallow, the main vein and its surroundings remain green, palmate mottled leaves, thickened leaves, curled leaf margins, leaves gradually falling from the bottom, leaving only a few leaflets at the top, sparsely populated bells, bolls cracking in advance The late diseased plants gave birth to tiny new shoots. Longitudinally cut stems produce light brown discolored stripes on the xylem. After acute rainstorms in summer, symptoms of acute wilting occurred. The cotton plants suddenly drooped and the leaves fell off in large numbers. The severely affected land was terribly catastrophic, resulting in a severe reduction in production. Due to the different pathogenicity of pathogens, the symptoms are also different. Divided into deciduous or light stalk type, spotted type or palmificial spot type and macular type. The deciduous type strain has strong pathogenicity. The chlorosis wilting of the diseased plant leaves or veins suddenly appeared from the leaves, and the diseased leaves rapidly changed from pale yellow to tan. The tip of the tip of the main stem of the diseased plant turned brown and died, and the diseased bell and wrapped leaves became brown and dry, buds and flowers. A large number of bells fell off. Only after about 10 days, the diseased plant became a light stalk, and the vascular bundle of the diseased stem turned yellow-brown in the longitudinal section, and the disease continued to the top of the plant. The symptoms of the leaf spot type are local spotting or palmoplantar spotting, falling off after desiccation and being caused by a moderately pathogenic strain. The pathogenicity of macular pathogenic bacteria was weak, yellow patches appeared on the leaves, and later expanded into palm-like yellow strips, and the leaves did not fall off. After a long period of high temperature and drought, in the event of heavy rain or flooding, the leaves have not yet appeared.
Symptoms, the plant suddenly wilted, the leaves quickly fall off, the cotton plant became a light stalk, and the vascular bundle became light brown when the stem was cut open. This is an acute type of Verticillium wilt. The disease is not dwarfed and it can produce a small amount of bolls. Sometimes the two symptoms of verticillium wilt and blight appear in the same cotton plant, but the symptoms are often related to the type and quantity of invading pathogens, and there are more complicated situations, which can be identified by necropsy. Verticillium wilt and wilt disease all cause discoloration of vascular bundles. Verticillium wilt lesions are lighter in color, mostly yellow-brown; blight is dark in color, mostly dark brown or black. The vascular bundles of stems, branches, and petioles of severely affected cotton plants are all discolored. If necessary, the microscope can be diagnosed.
The pathogen Verticilliu dahliae Kleb called Verticillium dahliae and V. albo-atrum Reinke et Berthold called Verticillium wilfordii, both of which belong to the subphylum Fungi. Our country is mainly the former. Verticillum dahliae Mycelia Whiterace, conidiophore erect, length 110-130μm, rounded branches, 3-4 branches per national record, branch size 13.7-21.42.3-9.1 (μm), round Shoots are conidial on top or top branches. Conidia are oval in shape, and cells are colorless, with a size of 2.3-9.11.5-3.0 (μm). The thickening of the spore wall results in the formation of black-brown chlamydospore, and many thick-walled cells combine into a nearly spherical microsclerotia, 30-50 μm in size. The bacteria have different pathogenicity in different regions and different species. The Americanization includes T1 type and SS-4 (non-leaf type) two physiological races. Symptoms caused by type T1 are downward curling of the parietal lobe, rapid detachment, and premature death. SS-4 led to yellow mottled veins between the main veins, slightly upward roll, the disease than the leaves off slightly, plant dwarfing. Type T1 is 10 times more pathogenic. The former Soviet Union is divided into race 0, race 1 and race 2. Race 2 is highly pathogenic. China is divided into three physiological types, and physiological type No. 1 has the strongest pathogenicity, represented by the Fungi strain of Shaanxi; physiological type No. 1 has the strongest pathogenicity, and Shaanxi Fuyang strain is the representative; physical type No. 2 is pathogenic. Weakness is represented by the Xinjiang Hetian flora; physiological type 3 is found in Jiangsu similar to the U.S. strain T9.
The transmission path and the disease conditions of the diseased plant strains can be carried on the organization, petiole, veins, leaf meat carrier rate was 20%, 1363% and 6.6%, diseased leaves as the disease in the soil is an important source of bacteria transmission of the disease . The rate of cottonseed feeding is very low, but it is an important way to spread long distances. The bacteria directly infects the roots in the soil. The bacteria pass through the cortical cells and enter the catheters to reproduce. The resulting conidia and mycelium block the catheter. In addition, the verticillium toxin produced by the pathogen is also an important pathogenic factor. Toxin is a kind of Acid glycoprotein, has a strong atrophic effect. The suitable onset temperature is 25-28°C, which is slower than 30°C and lower than 22°C. The incidence of cryptosis is higher than 35°C. In an appropriate temperature range, humidity, rain, and rainfall are important factors in determining the disease. The ground temperature is high, the number of sunshine hours is high, and the number of rainy days is small. On the contrary, the incidence is heavy. The suitable temperature in the field, the rain is more and more uniform, the monthly rainfall is more than 100mm, the rainy day is about 12 days, and the relative humidity is more than 80%. The buds usually occur sporadically, and the flowering period enters the peak of onset. Continuous cropping of cotton fields, application of uncontaminated organic fertilisers, and cotton fields lacking phosphorus and potassium fertilizers are prone to disease. Flooding and flooding often cause disease areas to expand.
Prevention methods (1) Protection of disease-free areas. Do a good job of quarantine and prevent the ward from expanding. (2) Selection of disease-resistant varieties. The high resistance variety is Xinluzhong No. 2. Disease resistant varieties include Liaomian No. 5, Liaomian No. 10, Liaomian No. 7, Zhongmian No. 9, Zhongmian No. 1 and No. 19, Zhongmian No. 99, No. 3723, No. 8004, No. 8010, Jin No. 68-420. , 86-4, 86-12, Jinmian 21st, 16th, Xiangmian 16, Hubei Cotton 3, Pro 66610, etc. Disease-resistant varieties include Jin No. 2031, No. 18 Zhongmian, Jin No. 252, and Lu 343. In areas where Verticillium wilt and Fusarium are mixed, they provide varieties resistant to Verticillium wilt and Fusarium wilt. For example, Shaanxi 1155, Liaomian No. 5, Liaomian No. 7, Zhongmian No. 12 (381), Yumian No. 4, Yumian No. 15, Zhongmian No. 17 and Zhongmian No. 16 etc. (3) Implement a large area of ​​rotation. Promoting rotation with grass crops, especially with rice rotation, has the most obvious effect. (4) Eradicate sporadic wards, control minor wards, and rehabilitate severe wards. For the cotton field with more than 0.25 strains of disease, manually remove the diseased plant, excavate the diseased soil, or use 16% ammonia or chloropicrin, formalin, and 90-95% alkaloid powder to fumigate or disinfect the soil. In the peak season of June to July, the disease-centered disease is the center of the diseased plant. 25 wells with a depth of 20 cm per m2 are injected into each well. Each well is filled with ammoniated bitter 5 ml (125 ml), and the soil is filled with water and soiled to protect against evaporation. , Then use 120 times crude crude emulsion or more than 6% ammonia solution containing ammonia 1:1 5L to eradicate, you can eliminate the disease point of Verticillium dahliae, generally per liter of 25% irrigating solution. It is also possible to treat the soil with 3.6 kg of active ingredient per 667 m2 of 90%-95% cotton. In the peak period of September-October, 90 ml of chloropicrin stock solution was evenly injected, and a significant effect was obtained. The disease-free, disease-resistant or disease-resistant varieties are mainly used in disease-free fields of 0.2%-5%, and disease-free soil-prepared cotton seedlings are transplanted and transplanted to control the occurrence of the disease; Reduce groundwater level, increase phosphorus and potash fertilizers to improve disease resistance and disease resistance, and remove diseased bodies. Diseased plants with more than 5% of severe disease fields mainly depend on planting disease-resistant, disease-resistant varieties and crop rotations. In recent years, 12.5% ​​Zhiweiling liquid agent 200-250 times liquid, in the early onset, during the flooding of each irrigation, per plant irrigation good liquid 50-100ml, 80% -90% control effect. (5) Cotton seed disinfection. Take concentrated sulfuric acid with a specific gravity of 1.8 and put it in a casserole and other containers and heat it to 110-120°C. Pour it into cottonseeds in a ratio of 1:10. While stirring, wait until the hair on the cottonseed is completely dark, wash thoroughly with clean water. Net, and then 80% of the antibacterial agent 402, the amount of 265-3 times the seed weight is heated to 55-60 °C after soaking cottonseed for 30 minutes, can effectively kill the inside and outside of cotton seed blight and verticillium wilt Bacteria. Can also be used 50% carbendazim wettable powder 10g dissolved in 25ml of 10% dilute hydrochloric acid, 975ml of water, plus 0.3g Pingpingjiao (cotton spinning penetrant, can also be used Hayao brand detergent to replace) 1000ml medicine Liquid, and then soaked for 15 hours at room temperature according to 17.5-20 kg for each 5 kg cotton seed liquid. Carbendazim can also be used as a 0.3% suspension in soaking in the greenhouse for 14 hours. (6) Health care cultivation. Reduce the frequency and concentration of organophosphorus pesticides such as phoxim and methamidophos to prevent cotton plants from being harmed by phytotoxicity and reduce their own disease resistance. Do not apply excessively, apply nitrogenous fertilizer, do a good job of combining nitrogen and phosphorus, pay attention to increase potassium fertilizer, and increase resistance to disease. Improve the ecological environment of cotton fields to make the soil temperature of cotton fields higher, but the humidity should not be too large, avoid flood irrigation, can reduce the incidence. (7) Biological control. Actinomycetes have a strong inhibitory effect on Dali. Some species of Bacillus and Pseudomonas in bacteria can effectively inhibit the mycelium distribution of Verticillium dahliae. Trichoderma lignorum has strong antagonism against Verticillium dahliae and can be used to change the soil microflora to reduce the incidence.
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