The potato virus A (PVA) causes the disease mild or crinkled mosaic. Leaves of infected plants show light green to yellow areas, with sometimes dark green patterns. The stems tend to bend outward. This virus is transmitted by at least seven species of aphids, including Myzus persicae, which also feeds on peach trees, and Macrosiphum euphorbiae, commonly known as the potato aphid.
Most strains of the potato virus S does not show symptoms when attacking potato plants. However, some potato cultivars shows a slight deepening of the leaf veins and some change of color from green to brownish. At harvest, losses can reach up to 20 percent, but mature plants are often more resistant to the virus.
Also called latent mosaic, the potato virus X is the most widespread in the world. Although some strains of this virus do not cause visible symptoms, contaminated plants can show 15 percent loss in their production. At temperatures lower than 68 degrees Fahrenheit, symptoms are more visible. Like PVS, PVX is not transmitted through insects, but by contact with contaminated stem tubers, sprays and other machinery used in the field.
The potato virus Y is the most severe of all mosaic viruses attacking potato plants. The symptoms range from mild marks and brown streaks on leaves and veins to defoliation and death. The mottling on the leaves is masked with temperatures lower than 50 degrees Fahrenheit. This virus also attacks eggplants, peppers and tomato plants. More than 20 species of aphids work as vectors of the PVY virus.