Tomato mosaic virus and tobacco mosaic virus
Tomato mosaic virus (ToMV) can cause yellowing and stunting of tomato plants, resulting in loss of stand and reduced yield. In addition, the virus may cause uneven ripening of fruit, further reducing yield. Tobacco mosaic virus (TMV) was once thought to be more common on tomato, but the two viruses are hard to distinguish easily and tobacco mosaic virus is usually (though not exclusively) more of a tobacco pathogen than a tomato pathogen.
Host and pathogen
ToMV infects tomato most commonly, but the virus can also infect pepper, potato, apple, pear, cherry, and numerous weeds, including pigweed and lamb's quarters. Symptoms may differ on different hosts. TMV has a very wide host range, affecting numerous crops, ornamentals and weeds including cucumber, lettuce, beet, pepper, tomato, petunia, jimson weed, and horsenettle.
Signs and symptoms
- Overall, tomato mosaic virus symptoms can be varied and hard to distinguish from other common tomato viruses. A definitive diagnosis can be accomplished by submitting a sample to the University of Minnesota Plant Disease Clinic.
- Mottled light and dark green on leaves.
- If plants are infected early, they may appear yellow and stunted overall.
- Leaves may be curled, malformed, or reduced in size.
- Spots of dead leaf tissue may become apparent with certain cultivars at warm temperatures.
- Fruits may ripen unevenly.
- Reduced fruit number and size.
- Yellowish rings may form if fruit ripens in warm weather.
- Fruits may show internal browning just under the skin (brownwall).
- Symptoms may be suppressed during cool temperatures. As a result, infected seedlings may not display symptoms until moved to a warm environment.
Biology and disease cycle
Tomato mosaic virus and tobacco mosaic virus can exist for 2 years in dry soil or leaf debris, but will only persist 1 month if soil is moist. The viruses can also survive in infected root debris in the soil for up to two years. Seed can be infected and pass the virus to the plant but the disease is usually introduced and spread primarily through human activity. The virus can easily spread between plants on workers' hands, tools, and clothes with normal activities such as plant tying, removing of suckers, and harvest. The virus can even survive the tobacco curing process, and can spread from cigarettes and other tobacco products to plant material handled by workers after a cigarette. Proper hand washing and sterilization of tools and equipment is essential to preventing spread this disease. Once inside a plant, the virus multiplies resulting in the symptoms described above.
There are numerous tomato varieties that are resistant to one or the other of the viruses. These are usually denoted in seed catalogs, often with the code ToMV after the variety name if resistant to tomato mosaic virus and TMV if resistant to tobacco mosaic virus. There are only a few varieties that are resistant to both viruses. Several popular rootstocks for grafted tomatoes can also confer resistance to varieties that may not normally be resistant.
Table 1: Tomato varieties resistant to ToMV and TMV
|ToMV Resistant||TMV Resistant||Resistant to both||Resistant Rootstock|
|Bolseno||Big Beef||BHN-444||Estamino (ToMV)|
|Tomimaru Muchoo||Celebrity||Health Kick||DRO138TX (ToMV)|
|Pink Wonder||BHN-871||Sophya||Colossus (TMV)|
A more extensive list of resistant tomato varieties can be found at Cornell University's Vegetable MD Online webpage.
- Use certified disease-free seed or treat your own seed. One method of seed treatment is to soak seeds in a 10% solution of trisodium phosphate (Na3PO4) for at least 15 minutes. Another method is to heat dry seeds to 158 °F and hold them at that temperature for two to four days.
- Purchase transplants only from reputable sources. Ask about the sanitation procedures they use to prevent disease.
- Inspect transplants prior to purchase. Choose only transplants showing no clear symptoms.
- Avoid planting in fields where tomato root debris is present, as the virus can survive long-term in roots.
- Wash hands with soap and water before and during the handling of plants to reduce potential spread between plants.
- Disinfect tools regularly — ideally between each plant, as plants can be infected before showing obvious symptoms. Soaking tools for 1 minute in a 1:9 dilution of germicidal bleach has been shown to be highly effective. Alternatively, a 1-minute soak in a 20% weight/volume solution of nonfat dry milk and water is also very effective. For either method, it may be most efficient when pruning plants to have two pruners and alternate between them between plants to allow proper soaking time.
- Avoid using tobacco products around tomato plants, and wash hands after using tobacco products and before working with the plants. Tobacco in cigarettes and other tobacco products may be infected with either Tomato mosaic virus or Tobacco mosaic virus, both of which could spread to the tomato plants.
- Scout plants regularly. If plants displaying symptoms of ToMV or TMV are found, remove the entire plant (including roots), bag the plant, and send it to the University of Minnesota Plant Diagnostic Clinic for diagnosis.
- If ToMV or TMV is confirmed, employ stringent sanitation procedures to reduce spread to other plants, fields, tunnels, and/or greenhouses.
- Completely pull up and burn infected plants. Do not compost infected plant material.
- After working with diseased plants, thoroughly disinfect all tools and hands as outlined above.
- For added security against spread, keep separate tools for working in the diseased area and avoid working with healthy plants after working in an area with diseased plants.
- At the end of the season, burn all plants from diseased areas, even healthy-appearing ones, or bury them away from vegetable production areas.
- Disinfect stakes, ties, wires, or any other equipment between growing seasons using the methods noted above.
There are currently no chemical options that are effective against either virus.