Rhizoctonia solani of potato

Rhizoefoniasolani Kühn

[Host crops] Solanaceae, legumes, gramineae and other crops, host a wide range.

[Disease diagnosis] It mainly damages buds, stem bases and tubers. The young bud is infected, and the ununearthed one causes rot, forming bud rot, resulting in lack of seedlings; after being unearthed, the disease begins to yellow the lower leaves, and brown concave spots occur at the base of the stem, 1~6 cm in size. The spots and their surroundings are often covered with purple hyphae; sometimes there are sclerotia of different sizes (1~5 mm) and shapes (massive or flaky) on the base of stems and tubers. Mild disease symptoms are often not obvious, serious disease plants can form withered or wilted top, or leaves appear curly. The pathogen was Rhizoctonia solani. Mycelia developed stout, multi-branched, branches almost right-angled, branch base more constricted, and often with close to the branch separation. Mycelia colorless at the beginning, brown gradually after maturity, cells become thick and short compression. A large number of hypha gathered kinks can form sclerotia. Sclerotia early pale brown, dark brown to dark brown, spherical or not shaped, 1~5 mm in size.

The fungus overwinters by sclerotiorum on diseased tubers or remains in soil. Seed potato with fungus was the main source of infection in the following year and the main route of long-distance transmission. Sowing diseased potato or sowing in diseased soil, the pathogen can cause disease in the bud by wound or direct infection, causing bud rot or later forming diseased seedlings. Pathogens can be transmitted by wind and rain, irrigation, insects and agricultural practices, and expand damage. Later up and down expansion caused by wilting on the ground or underground potato pieces with bacteria, sclerotia and then winter. Pathogens prefer warm and humid conditions. The soil temperature is about 23℃, and the disease is serious under humid conditions. The higher temperature of 23~28℃ was needed for sclerotia formation in late stage. In the north, cold, wet conditions in spring are prone to disease. Sowing early in spring, the disease is serious when the soil temperature is low. Heavy soil viscosity, low-lying water return slurry land, not easy to increase ground temperature, easy to induce disease. The incidence of disease in continuous cropping land was higher.

(1) Selection of resistant varieties. The varieties with excellent agronomic characters and resistance can be selected according to local conditions. (2) Use disease-free seed potatoes. The disease-free field is established and disease-free seed potatoes are used for sowing. (3) Improving farming systems. Appropriate rotation in seriously ill areas; planting in higher terrain; planting in seriously ill areas, sticky plots, low-lying areas with ponding, and cold mountain areas at high altitude, especially late sowing at appropriate times to prevent diseases induced by low ground temperature. (4) Disinfection of seed potatoes. Before sowing, seed potatoes were soaked in 500 times solution of 50% carbendazim WP, or 1000 times solution of 50% thiram WP, or 1500 times solution of 5% validamycin aqueous solution, or 450 times solution of 15% hymexiline aqueous solution, or 1500 times solution of 20% chlorfos-methyl EC for 10 minutes.