Types of Potato Mosaic Virus
As mentioned, there are different mosaic viruses that afflict potatoes, each with similar symptoms. Positive identification requires the use of indicator plant or laboratory examination. With that in mind, diagnosis can be made by mosaic patterns on foliage, stunting, leaf deformities, and tuber malformations. The three types of recognized mosaic virus in potatoes are Latent (Potato virus X), Mild (Potato virus A), Rugose or Common mosaic (Potato virus Y).
Signs of Potato Mosaic
Latent mosaic, or Potato virus X, may produce no visible symptoms depending upon the strain but yields of infected tubers may be reduced. Other strains of Latent mosaic show light leaf crinkling. When combined with Potato virus A or Y, crinkling or browning of leaves may also be present. In an infection of Potato virus, A (mild mosaic), the plants have light crinkling, as well as mild yellow mottling. Leaf margins may be wavy and appear rough with sunken veins. Severity of symptoms depends on the strain, cultivar and weather conditions. Potato virus Y (Rugose mosaic) is the most severe of the viruses. Signs include mottling or yellowing of leaflets and crinkling that is sometimes accompanied by leaf drop. Underside leaf veins often have necrotic areas showing as black streaking. Plants may be stunted. High temperatures exacerbate the severity of the symptoms. Again, symptoms vary hugely with both potato cultivar and virus strain.
Managing Potatoes with Mosaic Virus
Potato virus X can be found in all varieties of potato unless certified virus free tubers are used. This virus is spread mechanically by machinery, irrigation equipment, root to root or sprout to sprout contact, and via other gardening tools. Both viruses A and Y are carried in tubers but are also transmitted by several species of aphids. All of these viruses overwinter in potato tubers. There is no method for eradication of the disease once the plant is infected. It should be removed and destroyed. To prevent infection, use only seed certified free from viruses or that have low incidence of infected tubers. Always keep garden tools as clean as possible, practice crop rotation, keep the area around the plants weed free, and control aphids.
