Symptoms The disease is a bacterial vascular disease. The upper part of the disease is divided into two types of blemishes and wilting. The most common type of disease is the onset of the compound leaf on the base of the plant. The tip, leaf margins, and veins are green. The mesophyll is yellow-green or grayish-green. It is markedly mottled, and the tip of the leaf is dry or inward, and the condition expands upward. , The whole plant withered; early wilting type began to wilt from the apical compound leaves, leaf margin slightly inward, like water-deficient, the disease spread downward, the whole plant leaves began to chlorosis, sagging in the end, eventually causing plant lodging and death. The tuberculosis incision shows that the vascular bundle becomes milky yellow to dark brown, and the cortex has a ring-shaped or arc-shaped necrotic area, so it is called ring rot. After storage, the tuber buds become black and dry or the surface is burst, and after sowing, no buds or buds die or form diseased plants. The vascular bundles of the roots and stems of the diseased plants often turn brown, and the diseased vines sometimes overflow with white bacteria and pus.

The pathogen Clavibacter michiganense subsp. sepedonicum (Spieckermann & Kotthoff) Davi 6, Gillaspie, Vidaver and Harris. The synonymous Corynebacterium sepedonicum (Spieck. & Kotthoff) Skap-tason & Burkholder called the Corynebacterium michigans of potato ring rot disease bacterium, or Corynebacterium circulans, is a bacterium. The cells are short rod-shaped, with a size of 0.8-1.20.4-0.6 (μm), no flagella, single or even double, do not form decidua and spores, aerobic. The colonies were white in culture medium, thin and transparent, shiny, slow growth under artificial culture conditions, positive Gram stain.

Transmission routes and disease conditions The fungus grew winter in seed potatoes and became the source of infestation early in the year. After the diseased potato was sown, some buds rotted and did not germinate, and some of the unearthed diseased shoots grew. The pathogens rose along the vascular bundle to the middle of the stem or entered the new tuber along the stem and became pathogenic. Suitable for the growth temperature of the bacteria 20 to 23 °C, the highest 31 to 33 °C, the lowest 1-2 °C. The lethal temperature is 50°C for 10 minutes in a dry condition. The optimum pH is 6.8-8.4. The main route of transmission is the cutting of the fungus through the cutter when the potato is cut.

Control methods (1) Establish a disease-free field and plant whole potatoes as much as possible. The best conditions are best combined with new varieties of breeding, using hybrid seedlings to breed disease-free seed potatoes. (2) Planting disease-resistant varieties The strains identified as resistant to disease include: Dongnong 303, Zhengshu No. 4, Ningzi No. 7, Shaoshan White Peel, Ummun 601, Kexin No. 1, Fengding 22, Iron canister 1 No. 4, Aquila, Changshu No. 4, Plateau No. 3, Tongza No. 8 and others. (3) Remove diseased potato before sowing. The seed potatoes were placed in the room for five or six days before being air-dried, and the rotten potatoes were continuously removed to reduce the ring rot in the field. In addition, 50 mg/kg copper sulphate-spore seed potato has better effect for 10 minutes. (4) Combine cultivating soil with cultivators, remove the diseased plants in time, and take them out of the field for centralized treatment.

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