Potato Mosaic

Wild potato mosaic virus (WPMV) is a plant pathogenic virus of the family Potyviridae.The Potyviridae are a family of plant viruses. They are flexuous filamentous rod-shaped particles. Their genome is composed of positive-sense RNA which is surrounded by a protein coat made up of a single viral encoded protein called a capsid. All induce the formation of virus inclusion bodies called cylindrical inclusions (‘pinwheels’) in their hosts. These are composed of a single protein (70 kDa) made in their hosts from a single viral genome product.

Symptoms:

1. Latent mosaic:Standard varieties of potato are symptomless carriers of the latent mosaic virus. Some other varieties, when infected, respond with an acute systemic reaction commonly known as top necrosis killing the top of the main stem or a branch and processing downwards until the plant is killed. Tuber production may be prevented or if smaller tubers are formed they commonly show internal necrosis. Still other varieties may show mottling, stunting, necrotic spots on leaves and in some cases necrotic spots in the tuber.
2. Mild Mosaic:This disease is caused by one of the several strains of mild mosaic virus. Symptom on susceptible varieties is mottling and stunting which is favoured by cold temperature. Affected plants produce undersized tubers. When some strain of latent mosaic virus is present in mild mosaic affected plant; synergistic effect of both viruses give strong symptoms.
3. Rugose Mosaic:This disease is incited by the vein-banding virus. Mottling is inconspicuous in most cases. Rugosity and mottling of the surface of the leaflets together with some stunting are the most prominent early symptoms. Necrosis usually follows, starting as individual spots on leaflets and progressing until the entire leaf dies, sometimes dropping but often clinging to the stem. Necrosis is most severe on the lowest leaves and progresses upward slowly; a tuft of rugose leaves often persisting at the tip until the top dies prematurely. The tubers ordinarily show no symptoms other than the reduction in size induced by the damage to the top. If some strain of latent mosaic virus is also present, synergistic effect produce strong symptoms in this case also.
4. Yellows or Leaf Curl:It cause curling or rolling of leaves and top leaf becomes yellow in color. Plants do not grow properly and remain stunted. Tubers are also smaller in size. The loss in yield is up to 50% transmitted by aphid

Causal agents:

• Latent mosaic virus (Virus A)
• Mild mosaic Virus (Virus X)
• Vein banding virus (Virus Y)
• Yellows or Leaf curl virus.

Disease Cycle:The chief means of perpetuation of the three potato viruses is by way of seed tuber. Local dissemination of the latent mosaic virus is by mechanical contact. Mild mosaic and vein banding viruses are aphid transmitted.

Epidimiology:Air temperature has a marked effect upon the expression of symptoms. Latent mosaic and mild mosaic are favored by cool temperatures in symptom expression, while rugose mosaic is enhanced by warm weather and suppressed by cool weather

Control:

1. Use of disease free certified seed.
2. Rouging of diseased plants and burying them deep in soil.
3. Insect control in case of Mild and Rugose mosaic.
4. Avoid working of labour and animals from diseased to health crop in case of latent mosaic virus.
5. Resistant varieties (like chippewa & Irish cobs).
6. Early harvesting of the crop.