Cotton angular spot

The disease is harmful not only to cotton seedlings, but also to adult stems and leaves and developing cotton bolls. At the seedling stage, the infected cotyledons showed waterlogged irregular or round spots, dark brown, and the severe cotyledons withered and fell off. The back of the infected leaves first produced dark green dots, then expanded into oil-stained ones, and the disease spots on the front of the leaves were polygonal, and sometimes the disease spots expanded in irregular strips along the veins, resulting in withered and yellow leaves. Stem infection present water status of the main disease spot, and then expand and blacken or rot, the disease part is sunken, the germs bend to one side. The disease of the top bud formed a "rotten top", resulting in the death of the whole plant. When the humidity is high, the disease secretes viscous yellow bacterial pus, which becomes thin film or broken into powder under dry conditions. Cotton infected with primary oil immersed dark green spots, and then expanded into nearly round or multiple lesions fused into irregular shape, brown to reddish brown, sunken part of the disease, young bolls falling off, boll part of the ventricular rot.

Pathogen Xanthomonascampestrispv.malvacearum (E.F.Smith) Dowson called Xanthomonas campestris var. aeruginosa (Xanthomonas campestris) belongs to bacteria. The cell is rod-shaped, 1.2-2.4 × 0.4-0.6 (μ m) in size, with 1-2 flagella at one end, capable of swimming and with capsule. Gram staining was negative. Light yellow round colonies were formed on PDA medium. The somatic cells often combine 2-3 into chain bodies. The growth of the bacteria was suitable for Shu 25-30), the highest was 36-38 ℃, and the lowest was 10 minutes. 50-51 ℃ killed in 10 minutes. But it can withstand high temperature of 80 ℃ and low temperature of-21 ℃ under dry condition. The strain has physiological differentiation and 18 physiological races have been identified.

The pathogen mainly overwintered on diseased bolls in seeds and soil, and spread by Rain Water spatter and insects after cotton sowing in the next spring. After borrowing rain on the cotton boll, the water film of the main body surface invaded from the stomata or cracks in the epidermis and insect injuries, propagated in the intercellular space, destroyed the tissue in the leaves, and produced symptoms after 8-10 days. The pathogen often invades the vascular bundle through the diseased tissue and then reaches the seed, causing the seed to carry bacteria. The pathogen on the bell shell falls into the soil with the diseased body and becomes the source of infection at the beginning of the next year. The disease is mainly spread by seeds, the seed carrying rate is 6% Mur24%, and survives within the seeds for 1-2 years. The cotton area of the Yangtze River basin occurred from June to September, and entered the peak period from July to August, during which the relative humidity was higher than 85%, the number of rainfall was high, and the size reduction was easy to occur. In case of typhoon and rainstorm, the disease was serious. Island cotton is susceptible to disease.

Prevention and control methods (1) after picking, the diseased plant remains in the cotton field should be removed in time and concentrated retting fertilizer or burning. (2) carefully selected cotton seeds, reasonable close planting, timely drainage after rain to prevent moisture retention, combined with inter-seedling and fixed seedlings to find diseased plants in time. (3) adopt the technology of formula fertilization, advocate the application of compost made by enzyme bacteria retting, and avoid excessive application of nitrogen fertilizer. (4) promote the use of ridge cultivation or high border, scientific irrigation, flood irrigation and series irrigation are strictly prohibited. Ploughing and releasing moisture in time. (5) seed treatment. Cotton seed cashmere carrier can be eliminated by using concentrated sulfuric acid. See Verticillium wilt of cotton. You can also soak the seeds in warm water (55-60 ℃) for half an hour. (6) selecting disease-resistant varieties. The system resistance of upland cotton is strong, and the disease resistance of medium cotton is also higher. (7) strengthen field management, apply fertilizer in time after typhoons and heavy rains, and spray 1 ∶ 1 ∶ 120 times Bordeaux solution or 25% clozole wettable powder solution or 72% agricultural streptomycin sulfate 4000 times solution.