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Symptoms and Control Methods of Potato Wart Disease

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[Pathogen scientific name] Synchytrium endobioticum (Schilb.) Percival [Host crops] Potato, tomato, black nightshade, etc. [Disease diagnosis] It mainly damages the underground parts of the plant, occurring commonly on tubers and stolons. On the eyes of infected tubers and on stolons, because the pathogen stimulates continuous cell division, tumors of varying size, irregular shape and rough, protruding surface form, resembling cauliflower. The surface of affected tubers often cracks. The wart tissue is yellow-white in the early stage, the part exposed above the soil surface turns green, and later turns dark brown. The tissue is soft, prone to rotting and produces a foul odor, with brown slimy matter. During storage, diseased tubers can still develop, even causing the whole storage cellar to rot. Diseased tubers turn black and give off a foul odor; after prolonged boiling they do not soften easily and are difficult to eat. When the aboveground parts are affected, the appearance does not differ noticeably from healthy plants, but in the later stage diseased plants are taller than healthy ones, remain green longer than healthy plants, have more branches and bear more berries. On severely diseased plants, stems, leaves and flowers can all be affected, forming wart lesions or deformities. The causal agent is the endobiotic chytrid fungus. The pathogen is endoparasitic and does not produce hyphae; the vegetative thallus is initially a naked, wall-less protoplast (amoeboid body), and later becomes a walled unicellular thallus. In the reproductive growth stage, the unicellular thallus transforms into a resting sporangium sorus. The sporangium sorus is nearly spherical and contains 4 to 9 sporangia. The sporangia are spherical, rust-brown, and on germination produce zoospores. The zoospores have a single flagellum and are spherical to pear-shaped. Some zoospores mate to form zygotes. The zygote resembles a zoospore and has two flagella; both can infect the host.

[Pathogen scientific name] Synchytrium endobioticum (Schilb.) Percival

[Host crops] Potato, tomato, black nightshade, etc.

[Disease diagnosis] It mainly damages the underground parts of the plant, occurring commonly on tubers and stolons. On the eyes of infected tubers and on stolons, because the pathogen stimulates continuous cell division, tumors of varying size, irregular shape and rough, protruding surface form, resembling cauliflower. The surface of affected tubers often cracks. The wart tissue is yellow-white in the early stage, the part exposed above the soil surface turns green, and later turns dark brown. The tissue is soft, prone to rotting and produces a foul odor, with brown slimy matter. During storage, diseased tubers can still develop, even causing the whole storage cellar to rot. Diseased tubers turn black and give off a foul odor; after prolonged boiling they do not soften easily and are difficult to eat. When the aboveground parts are affected, the appearance does not differ noticeably from healthy plants, but in the later stage diseased plants are taller than healthy ones, remain green longer than healthy plants, have more branches and bear more berries. On severely diseased plants, stems, leaves and flowers can all be affected, forming wart lesions or deformities. The causal agent is the endobiotic chytrid fungus. The pathogen is endoparasitic and does not produce hyphae; the vegetative thallus is initially a naked, wall-less protoplast (amoeboid body), and later becomes a walled unicellular thallus. In the reproductive growth stage, the unicellular thallus transforms into a resting sporangium sorus. The sporangium sorus is nearly spherical and contains 4 to 9 sporangia. The sporangia are spherical, rust-brown, and on germination produce zoospores. The zoospores have a single flagellum and are spherical to pear-shaped. Some zoospores mate to form zygotes. The zygote resembles a zoospore and has two flagella; both can infect the host.

[Occurrence pattern] The pathogen overwinters as resting sporangia in diseased tissue or with diseased plant residues in the soil. The resting sporangia are extremely resistant to adverse conditions and can survive in the soil for 25 to 30 years. When conditions are suitable, they germinate to produce zoospores, which invade through the host epidermal cells, then produce sporangia and stimulate host cell division and proliferation. The sporangia germinate to produce zoospores or zygotes, causing repeated infection. The pathogen infects easily under conditions of low temperature and high humidity, a cool climate, large day-night temperature differences, high soil moisture and a temperature of 12 to 24°C. Plots with loose soil, rich organic matter and a slightly acidic reaction are prone to the disease. There are differences in resistance among potato varieties.

[Control measures] (1) Strictly implement quarantine. It is strictly forbidden to ship seed potatoes out of diseased areas. (2) Select resistant varieties. The Yunnan variety Mila shows high resistance and can be chosen according to local conditions. (3) Arrange crop rotation sensibly. Choose cereal crops for rotation and eliminate potatoes grown in alternate years. On heavily diseased land, switch to non-solanaceous crops. (4) Strengthen cultivation management. Avoid low-lying, waterlogged land; apply thoroughly decomposed, disease-free fertilizer and increase the application of phosphorus and potassium fertilizer; destroy diseased plant residues. (5) Carry out chemical control well. Use 15% triadimefon at 400 to 500 grams per 667 sq m. The following can be used: ① Seed covering with treated soil: after sowing, cover the seed potatoes with treated soil at 1:200; ② Drenching the planting hole with solution: when 70% of the potatoes have emerged, drench the roots with a 1000-fold dilution; ③ Spraying with solution: spray once when 70% have emerged and once at the early bud stage, using 60 kg of a 1500-fold dilution per 667 sq m.

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