After the introduction of new potato varieties, as the number of planting years increased, the yield gradually declined. The plants became shorter, the tubers smaller, and the stems and leaves showed abnormal symptoms such as curled or shriveled leaves. This phenomenon is known as degradation. The primary cause of this degradation is viral infection, an infectious disease spread mainly by aphids or through direct contact between plant leaves.
Viral infections can disrupt the plant's physiological and metabolic processes, leading to reduced vigor and significant yield loss. In severe cases, production can drop by 70% to 80%, and in some instances, no marketable potatoes are produced at all. Globally, there are 18 known viruses that infect potatoes, including one virus and two types of mycoplasma. Nine of these viruses specifically target potatoes, while seven are commonly found in the country. These include Potato Virus X (PVX), Potato Virus Y (PVY), Potato Virus S (PVS), Potato Virus M (PVM), Potato Violet Mosaic Virus (PVMA), Potato Virus A (PVA), and Potato Leafroll Virus (PLRV). Additionally, some viruses that affect other crops like tobacco, cucumber, and tomatoes can also infect potatoes.
Common symptoms of potato virus diseases include mottled or mosaic patterns on leaves, where chlorophyll distribution is uneven, resulting in green or yellow patches. In severe cases, leaves may shrink, the entire plant becomes stunted, and veins or leaves may become transparent. Another type of symptom involves necrotic spots on leaves, petioles, shoots, and stems. These lesions often develop into necrotic streaks, and in extreme cases, the entire leaf may wither or wilt. Some infected leaves curl inward along the main vein or from the edges, becoming hard and leathery. In the worst scenarios, each leaflet may turn into a tube-like shape. Compound infections can lead to more severe symptoms like potato plague necrosis.
PVX causes light mosaic patterns on potato leaves, sometimes with mottled or ring-shaped spots. Its virions are linear, measuring 480–580 nm in length, and it has a wide host range. It primarily infects plants in the Solanaceae family. The virus dilution limit is 100,000 to 1,000,000 times, and it remains active for over a year at room temperature. PVS causes mild leaf shrinking or mosaicism, with linear virions 650 nm long and a narrow host range, mostly affecting Solanaceae plants. The sap dilution point is 1–10 times, and it is inactivated at 55–60°C, surviving only 3–4 days in vitro.
PVA causes mild mosaic or non-specific symptoms, with linear virions 730 nm long. It infects only a few Solanaceae species. The sap dilution point is 10 times, and it is inactivated at 44–52°C, surviving 12–18 hours in vitro. PVY causes severe mosaic or necrotic spots and streaks on leaves. Its virions are 730 nm long, and it has a broad host range, infecting many Solanaceae plants. The sap dilution point is 100–1,000 times, and it is inactivated at 52–62°C, surviving 1–2 days in vitro.
PLRV has spherical virions, 25 nm in diameter, and primarily affects Solanaceae plants. It induces leaf rolling in potatoes. The sap dilution point is 10,000 times, and it is inactivated at 70°C, surviving 12–24 hours in vitro. At low temperatures (2°C), it can survive up to 4 days. TMV can also infect potatoes.
The transmission of these viruses occurs mainly through aphids and plant sap. Poor field management and high aphid populations increase the risk of infection. Temperatures above 25°C weaken the plant’s resistance and promote aphid activity, facilitating disease spread. Cultivar resistance and proper farming practices play a crucial role in disease prevention.
Viral diseases are among the most serious threats to potato production. They cause metabolic disorders, reduce plant vitality, and lead to significant yield losses. With advancements in detection technology, it has been found that nearly all potato varieties are infected with at least one virus. Viruses replicate alongside the plant's normal metabolic processes, making chemical control ineffective. Many virus inhibitors can harm the plant itself, and once their use stops, the virus resumes its original concentration.
Chemical insecticides can help reduce the spread of some viruses by controlling aphid populations. However, viruses transmitted through direct contact or feeding (such as piercing-sucking insects) are not effectively controlled by insecticides. Early seedling harvesting, seed potato collection, and avoiding aphid transmission have proven effective in reducing virus spread.
Currently, methods to remove viruses from susceptible varieties include heat treatment and shoot tip culture. Using virus-free seeds is another effective approach. By producing virus-free seed potatoes, farmers can significantly improve yields. This method is widely used in mountainous areas of southwest China, Inner Mongolia, and Heilongjiang, with positive results.
Heat treatment, such as exposing tubers to 35°C for 56 days or 36°C for 39 days, has been shown to eliminate certain viruses. Recent advances include variable temperature treatments, particularly for bud-derived seed potatoes.
Selecting disease-resistant and virus-free seed potatoes is also critical. Some varieties show field resistance to specific viruses, but most Chinese cultivars lack resistance. Virus-free seedlings are typically obtained through tissue culture, and virus-free seed potatoes are propagated under isolation conditions for commercial use. Aphid control and removal of diseased plants are common practices.
Controlling aphids early, especially before and after emergence, is essential for preventing diseases like stripe mosaic virus, which is transmitted non-persistently. Appropriate insecticide use is recommended.
Improving cultivation practices is equally important. This includes keeping fields away from Solanaceae vegetables, removing diseased plants early, practicing intensive and raised-bed cultivation, timely soil cultivation, avoiding excessive nitrogen fertilizer, increasing phosphorus and potassium, weeding regularly, and managing water to prevent flooding.
In the early stages of infection, applying antiviral agents such as 0.5% mushroom proteoglycan diluted 300 times, 20% virus A wettable powder diluted 500 times, 5% bacterial water agent diluted 5.0 times, 1.5% disease Ling K emulsion diluted 1000 times, or 15% virus will WP diluted 500–700 times can be effective.
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