Causal Agent:
Tomato Mosaic Virus (ToMV). 
Several strains are known.

Vector:
Mechanically transmitted

Distribution:
Worldwide

Symptoms:
Typical symptoms include a light and dark green mottling of the leaf tissue and stunting of the plant. Foliar symptoms can vary from a chlorotic mottling to necrosis as well as upward leaf rolling and stem streaking depending on which strain of ToMV infects the plant. During cool temperatures leaves may develop a "fernleaf appearance where the leaf blade is greatly reduced, while during high temperatures foliar symptoms may be masked. Occasionally the fruit will show disease symptoms which vary from an uneven ripening to an internal browning of the fruit wall (brown wall). Brown wall typically occurs on the fruit of the first two clusters and appears several days prior to foliar symptoms. Under certain environmental conditions some varieties with resistance (heterozygous) to ToMV will show necrotic streaks or spots on the stem, petiole, and foliage as well as on the fruit.

Conditions for Disease Development:
ToMV has a wide host range including many agricultural crops and weeds, all of which can serve as inoculum sources. It is readily transmitted by machinery or workers from infected to healthy plants during handling. Infested debris from a previous crop can lead to infection when the roots of the new tomato plants come in contact with the debris. Chewing insects can transmit the virus, but are not considered a major source of infection. Tomato seed can carry the virus, but actual infection is thought to occur when plants are thinned or transplanted.

Control:
The use of ToMV resistant varieties is the best way to reduce losses from this disease. Avoid planting in soil from previous crops that were infected with ToMV. Steam sterilizing the potting soil and containers as well as all equipment after each crop can reduce disease incidence. Before handling containers or plants be sure all workers wash with soap and water. Sterilizing pruning utensils or snapping off suckers without touching the plant instead of knife pruning help reduce disease incidence. Direct seeding in the field will reduce the spread of ToMV.

Typical leaf mosaic symptoms.                       Severe leaf distortion and 
                                                                               chlorotic mottling.

Fern leaf foliar symptoms.

Necrotic fruit lesions.