Viral diseases
Viral diseases of importance include:
Potato Leaf Roll Virus (PLRV)
Potato X Potexvirus (PVX)
Potato Virus Y Potyvirus (PVY)
Under field conditions, there is often a composite infection with the 3 viruses (PLRV; PVX; PVY) and it becomes very difficult to distinguish the three on the basis of symptoms.
These viruses are transmitted by aphids. PVX causes distinct leaf mottling and crinkling. PVY causes dwarfing of plants, with a rough, mosaic appearance to the leaves and affected plants give a poor crop of small tubers. PVY is also tuber-borne. Potatoes infected with PLRV show an upward and inward rolling of leaflet margins and plants are dwarfed. Affected leaflets become thick and dry, and the lower leaves may become completely brown. Infected plants produce tubers smaller in size and numbers. PLRV also infects other solanaceous crops and weeds (e.g. tomato, tobacco, jimson weed).
- Use virus-free seed tubers.
- Plant resistant varieties where available. In Kenya, the following potato varieties are claimed to possess some resistance to viral diseases: "Kenya Baraka", "Roslin Eburu", "Feldelslohn", "Annet" and "Dutch Robjn".
- Uproot infected plants to reduce the incidence of infection and spread of the disease within a field. For maximum effectiveness remove the diseased plant, the 3 plants on each side of the diseased plant in the same row, and the three closest plants in adjacent rows. This is particularly important in seed fields.
- Control of insect vectors may reduce virus spread.
- Do not overlap potato crops.
- Practise good field sanitation.
- Control nightshades and volunteer potatoes because these plants are reservoirs for viruses
