Symptom

• Affected plants show leaves with molting or mosaic pattern of light green and dark-green areas.
• Primary symptoms appear on newly formed young leaves as vein clearing, greenish yellow motling.
• Infection on young plants results in stunted growth, malformation, distortion and puckering of leaves. Dark-green blisters and some time enations (leafy growth) appear on the dorsal side of the leaf.
• Immature leaves show varying degree of yellow motling and chlorosis. In severe infection due to a highly virulent strain of TMV, various necrotic dark-brown spots also develop resulting into 'mosaic scorch' or 'mosaic burn' under hot sunny dry spell, damaging large areas of lamina.
• There are many strains of TMV and symptom expression depends upon the strain and the prevailing environmental factors. Mosaic-affected leaves after curing show green spots which lower the market value of the leaf.

Transmission

• TMV is highly contagious and transmitted by sap. It is easily transmitted by mere contact of a diseased plant with a healthy one. 
  Air-dried tobacco is a common source of new infection. Workers who chew or smoke natural leaf tobacco during nursery operations may spread the virus into the seedlings.
• Old stems and leaf trash of affected plants buried in the soil are the other sources of infection and spread.
• In the nurseries, seedlings may get affected due to the presence of susceptible weed hosts.
• The virus is not insect transmitted. The aphid (Myzus persicae) which occurs commonly on the tobacco plant is unable to transmit the virus.
• TMV is highly infectious. Entry of TMV is direct through the epidermis and rarely through stomata. Entry depends upon the type of wound, toughness of epidermis, presence of inhibitors of virus and virus concentration.

Management

• Best effective way is to keep the crop mosaic free.
• Constant vigilance is required right from the seedling stage till harvest involving phytosanitary measures, and nothing can be done once TMV becomes systemic.
• Infected seedlings should be removed promptly and destroyed.
• Workers should disinfect their hands with soap and running water before handling seedlings, weeding or doing other cultural operations. 
  Use of tobacco (smoke, snuff, or chewing) should be prohibited strictly while working in seedbeds or field.
• Weeds (Solanum nigrum) and plant (Brinjal, Tomato, Chillies) susceptible to the virus should be destroyed.
• In fields showing high incidence of mosaic, rotation for 2 years should be followed.
• Rouging of the affected plants before first interculturing considerably reduces the spread of the disease.
• However, in areas where TMV is an over-riding problem, resistant lines developed at CTRI, Rajahmundry, viz. TMVRR-2 and TMVRR-2a, TMVRR-3 can be used to overcome this problem. 
  Spray leaf extracts of Basella alba, Bougainvillea (one litre of extract dissolved in 100-150 litre of water) on 30th, 40th and 50th days after transplanting.