Potatoes are a vegetatively propagated crop, and many disease organisms including several viruses are disseminated in tubers. The strict guidelines for an early generation or certified seed production reflect the significance that tubers have in the spread of viruses. The viruses include potato leafroll virus, potato viruses Y, X, A, S, M, and alfalfa mosaic virus, with the first three being the most important.
It is difficult to differentiate between symptoms of one virus and another, as they are all very similar. However, it is important to note symptoms of the same virus are often expressed very differently depending on the variety. Viruses may decrease yield from one generation to the next unnoticed by many farmers because some potato viruses are often referred to as latent viruses because they can be carried in plants or tubers without manifesting any symptoms.
Here are some viruses that attack plants:
Potato leafroll virus (PLRV)
Symptoms scored as Leafroll are caused by the Potato Leafroll Virus (PLRV) and is transmitted by aphid species. Other hosts of this virus include Solanaceous fields, such as, but not limited to tomato, pepper, eggplant, and tobacco. It is a serious disease that affects potato output in terms of quantity and quality and may disqualify a crop from certification.
Foliar symptoms of PLRV can be divided into primary and secondary infections:
- The primary infection is When a plant that was previously healthy is infected by aphids. The upper leaves become pale, upright, and rolled and show some reddening of the tissue around the leaf edges.
- Secondary infection occurs when an infected tuber is planted, giving rise to an infected plant. The lower leaves are severely rolled and leathery to the touch. When an infected tuber is planted, the result is the growth of an infected plant, which causes secondary infection. Severely curled and leathery to the touch are the lowest leaves. The overall appearance of the plant is typically upright, stunted, and chlorotic. The oldest leaves may show chlorosis.
PLRV can be difficult to detect because foliar symptoms are not always obvious. Thus infected tubers or tubers with net necrosis may result from plants without visual symptoms.
Control consists of suppressing aphid populations with systemic and (or) foliar insecticides and planting certified seeds.
Potato virus Y (PVY)
PVY is one of the most important viruses infecting potatoes. It is a virus spread by aphids that causes yield losses and tuber quality defects in commercial potato crops. In seed crops, PVY infection increases the risk of the seed lot being downgraded or rejected from certification.
PVY is tuber-borne and can interact with other viruses such as PVX and PVA to result in heavier losses.
Symptoms caused by PVY infection can vary depending upon the potato variety grown, plant age, and environmental conditions. Necrosis may progress to total leaf collapse, with the dead leaflet clinging to the stem. Infected plants are often stunted.
Potato Virus X (PVX)
PVX is one of the most widely distributed viruses of potatoes because no symptoms develop in some varieties (latent), the full extent of damage with PVX is not recognized. Mixed infections of PVX with other viruses like PVY and PVA cause more damage than PVX alone. PVX is tuber-borne and is readily mechanically transmitted by human activities. Tobacco, pepper, and tomato are additional hosts for this virus.
Potato Virus Mosaic (PVM)
Leaf symptoms referred to as mosaic result from potato plants being infected with certain potato viruses. It may be most important when found as mixed infections with other viruses and is transmitted by aphids. From mild leaf mottling to severe leaf crinkling and plant stunting, the symptoms can range in intensity. The expression of symptoms may also be influenced by the variety and/or climatic circumstances. The symptoms might be worse in cool, cloudy weather. Multiple viruses in the plant may affect symptoms and make them more severe.
General Symptoms of virus affected plants include; Leaves curling upward and turning pale yellow. If you press them they feel brittle and fragile. Advanced infections cause stunted growth and pale green, tightened leaf stems that stand straight. If a potato plant has a severe infection, it may only yield very small tubers or not at all.
Control of virus affected plants include;
- Use of disease-free seed: The use of certified seed should only be purchased from authorized sources.
- Removing, gathering, and killing plants that have viral infections because viruses can spread from one plant to another through vectors.
- Application of insecticides to control insects that can carry viral infections. Typically, sucking insects like aphids, thrips, mites, and whiteflies can transfer viruses.