Tobacco Mosaic Virus (TMV)
Thursday, 22 February 2007 15:11
Tobacco mosaic virus has a wide host range but is of special concern on solanaceous crops. TMV has been reported on ajuga, begonia, calibrachoa, chrysanthemum, cyclamen, epimedium, gazania, geranium, gerbera, helianthus, impatiens, lisanthus, lobelia, lysimachia, New Guinea impatiens, osteospermum, nicotiana, pepper, petunia, penstemon, tomato, torenia and verbena.
Symptoms include yellow and green mottling, upward leaf curling, necrotic leaf spots, leaf distortion, and overall stunting. In some cases, infected plants may not show any symptoms at all or some cultivars may not show obvious symptoms unless they are stressed. Overall stunting is often very hard to distinguish, especially if all of the incoming plants in a flat or plug tray are stunted.
TMV is not transmitted by insects! It is a very stable virus that is readily spread mechanically in sap, by contact with contaminated equipment, by vegetative propagation, and it can be carried in the seed.
Greenhouse workers can easily spread this virus when they handle plants or when cutting tools become contaminated with the virus. Since TMV can also persist in dried tobacco leaves, cigarettes and other tobacco products can be important sources of TMV. This is a way the virus can be transmitted to a healthy crop and why smoking should not be permitted in greenhouses, especially propagation houses!
Once a plant is infected with a virus, it cannot be cured. Treating with insecticides is not helpful, because there is no insect vector. Identifying infected plants can be difficult because the symptoms are often not distinctive. This is in contrast to the situation when impatiens are infected with Impatiens Necrotic Spot Virus (INSV) and exhibit distinct ringspots and black lesions on stems. Samples may be sent your state Diagnostic Laboratory (listed in last week's notice), sent to Agdia (www.agdia.com), or tested in house by purchasing ImmunoStiks for TMV from Agdia (www.agdia.com).
Tips on management:
• Discard and destroy infected plants including roots.
• Disinfect hands by washing with milk, or tri-sodium phosphate and then thoroughly with soap and water after handing infected plants or contaminated equipment or pots.
• Smokers must to wash their hands before entering the greenhouse so they do not infect plants.
• In greenhouses, hard surfaces such as doorknobs, or flats can become contaminated after handling virus-infected plants and remain a source of infection. Thoroughly disinfect the growing area with a commercial disinfectant such as ZeroTol, Oxidate, Green-Shield, Physan, or Triathlon.
• Control perennial weeds in the solanaceous family such as ground cherry and horsenettle in and around the greenhouse because they can be reservoirs of TMV.
Photos of TMV on Calibrachoa , 2 and TMV on Torenia
Sharon Douglas, Plant Pathologist, The Connecticut Agricultural Experiment Station, New Haven, CT
Leanne Pundt
