What are the control methods for potato virus diseases?

Potato virus disease is a major disease of potatoes. According to symptom manifestations, potato virus diseases are often divided into two major categories: potato mosaic disease and potato leafroll disease. In most areas of our province, potato mosaic disease is the predominant occurrence, generally reducing potato yield by 20%-50%, and by more than 80% in severe cases.

Symptoms

Common mosaic disease: after the plant is infected, growth is normal, leaves are flat, but there is mild mosaic between the veins, manifested as uneven shades of leaf flesh color. Light mosaic with alternating yellow and green is easily seen on the leaves. In some varieties, symptoms can be masked under both high and low temperatures, and infected tubers show no symptoms. However, there are certain differences depending on the potato variety, environmental conditions and virus strains; highly virulent strains can also cause wrinkling, streaks, necrosis, etc. Severe mosaic disease: in the early stage of the disease, mottled mosaic or necrotic spots appear on the top leaves, after which obvious black necrotic spots can form on both sides of the leaves, and necrosis can spread from the veins to the petioles and main stem, forming brown streaks, causing the leaves to necrose and dry up and the plant to wilt. Different varieties react differently; for example, the plant may be short, the internodes shortened, and the leaves may appear as common mosaic, with leaves and stems becoming brittle. Plants grown from virus-carrying seed potatoes can be severely stunted and wrinkled or show streak mosaic, and symptoms can also be masked. The tubers of diseased plants become smaller.

Wrinkled mosaic disease: the diseased plant is stunted, the leaves are small and severely wrinkled, mosaic symptoms are severe, the leaf tips bend downward, and there are dark brown necrotic spots on the veins, petioles and stems, and the diseased tissue becomes brittle. When damage is severe, the leaves are severely wrinkled and die from the bottom upward, and mottling can be seen on the top leaves. The tubers of diseased plants are relatively small and may also have necrotic spots.

Leafroll disease: the typical symptom is upward curling of the leaf margins, becoming cylindrical when the disease is severe. In the early stage it appears on the young leaves at the top of the plant; first they become chlorotic, then curl upward along the midrib, spreading to the old leaves. The leaves are small, thick and brittle, the veins are hard, the leaf color is pale, and the underside of the leaves can be red or purplish red. The diseased plant is stunted to varying degrees; because the phloem is destroyed, black spots can be seen in the cross-section of the stem, more obviously at the stem base and nodes. The tuber tissue shows net-like necrotic markings in the vascular region.

Spindle tuber disease: the affected plant has few branches and is upright, the leaves are held upward, small and brittle, and often curled. Near the stem, the internodes are shortened; at budding stage the plant's slow growth is clearly seen, the leaf color is pale, sometimes yellowing, and severely diseased plants are stunted. The tubers become smaller and longer, tapering at both ends into a spindle shape. The number of eyes increases and they protrude, the area around them is brown, and the skin is smooth.

Disease control

1. Select good disease-resistant varieties There are many kinds of potato virus diseases, and one virus often has several strains; each strain reacts differently on each potato variety, so virus-resistant breeding is very complex, and it is difficult to obtain varieties resistant to multiple viruses at the same time. Therefore, varieties should be selected in a targeted way according to the main local viruses. At present, widely planted virus-resistant varieties include: Neishu No. 7, Atlantic, Zhongshu No. 2, etc.

2. Summer sowing and two-crop seed production This is an effective method to prevent seed potato degeneration and solve the problem of retaining seed locally. In areas with a short frost-free period, normal spring sowing can be postponed to summer sowing for seed production (sowing from late June to early to mid-July); in areas with a long frost-free period, potatoes are planted twice a year, that is, sown in spring and autumn, with autumn-sown potatoes used as seed. In this way, seed potatoes are not only beneficial for vigorous potato growth, but can also control the speed of virus multiplication and spread.

3. Chemical control Timely control of aphids in seed production fields has a significant effect on reducing degeneration, especially on leafroll virus. Virus inactivating agents can also be used, such as 20% Dubingling, 2% Ningnanmycin, etc.

4. Strengthen cultivation management The purpose is to promote early maturity, ensure increased yield, and avoid tuber formation under high temperatures. To this end, sowing must be timely according to local conditions, high beds should be used for cultivation, fertilizer should be applied rationally, diseased plants should be pulled out, and cultivation and hilling should be done frequently.