Potato spindle tuber disease

[Virus English name] Potato spindle tuber viroid

[Host crops] Potato, tomato, etc.

[Disease diagnosis] Diseased plants have upright stems with very few branches. Leaves are held upright, and the angle between the petiole and the stem becomes smaller; leaf margins are wavy or curl upward, and leaves are stiff and brittle with a dark green color; leaves become smaller and curl into a half-closed, twisted shape. At the bud stage, plant growth is noticeably delayed, leaf color becomes lighter and sometimes yellowed, and severely diseased plants are stunted. Tubers are elongated, or one end is more pointed, forming a spindle shape, and some are pear-shaped or deformed; eyes increase in number and become flat and shallow, sometimes protruding, with prominent eyebrow ridges. Red- and purple-skinned varieties lose color when diseased, and the skin is smoother than that of healthy tubers, sometimes with cracking. In some varieties, brown spots appear near the eyes; in others, tumors appear on the tubers, showing deformity. The causal virus is Potato spindle tuber viroid. The virus particle is an extremely small RNA molecule, circular, with no protein coat. The inactivation temperature is 65-80°C, the dilution endpoint is 0.001-0.0001, and the survival period in vitro is 3-5 days.

[Occurrence pattern] The virus is carried by seed potatoes and then transmitted or spread by sap, insects, seeds, or other means. It is mainly spread mechanically, primarily by human activity such as contact with cut tuber surfaces and by cutting knives; in the field, it is spread by aphids, stink bugs, leaf beetles, and others; the virus-carrying rate of seeds harvested from plants is about 6%-89%. Virus-carrying seeds germinate slowly, seedlings grow slowly, and plants become yellowed, stunted, or even show bunch-top symptoms. Sowing virus-carrying seed potatoes produces virus-carrying plants, and insects accelerate spread, worsening the damage. High temperatures favor viroid reproduction and aphid reproduction and activity, are unfavorable for tuber growth resistance, and easily lead to disease occurrence and epidemic. Conversely, in years and regions with greater temperature differences, the disease is milder. The virus-carrying rate of seed potatoes is related to the number of initial diseased plants in the field and affects disease severity. Disease resistance differs markedly among potato varieties.

[Control measures] (1) Select disease-resistant varieties. Relatively resistant varieties include Dongnong 303 and others, and suitable varieties can be selected locally according to conditions. (2) Use virus-free seed potatoes. Establish disease-free seed production fields, and introduce seed potatoes only after testing confirms they are virus-free. (3) Reduce human spread. Adopt whole-tuber direct sowing to avoid the virus transmission step of cutting and reduce mechanical spread; during field farming operations, avoid tool-caused damage and contact between plants or leaves that spreads the virus. (4) Disinfect cutting knives. When cutting seed potatoes, the knives used (and tools) should be soaked or rinsed at any time with 0.25% sodium hypochlorite solution or 1.0% calcium hypochlorite solution to reduce transmission. (5) Control aphids in time to prevent disease. Refer to other viral diseases. (6) Strengthen cultivation management. Prepare land carefully, sow at the appropriate time, cultivate on high ridges, ensure sufficient fertilizer and water, avoid tuber formation under high temperatures, and increase phosphorus and potassium fertilizer, etc., to slow the disease.