Protection Methods

- During cultivation

Unlike fungal diseases, there is no curative method to effectively control viruses and particularly tobacco mosaic virus (TMV) during cultivation. Generally, an infected plant will remain infected all its lifecycle.

If the infections occur in nurseries and are detected early, the plants showing TMV symptoms and also some surrounding, apparently healthy plants, should be quickly eliminated and in no case be transplanted later. All plant debris contaminated with the virus present in and on the soil should be removed and burnt. Workers should wash their hands frequently, before, during (several times) and after their activities in the nursery. They can use phosphate buffer solution or a detergent. Milk has long been recommended as an alternative. The tools should be disinfected in the same way.

Similar  measures should be taken in the field if symptoms appear on mature plants. At the end of the crop, it is advisable to eliminate as much as possible of plant debris, including root systems, in which the virus will survive longer than in bare soil.


- Next crop

A set of measures should be implemented in order to eliminate TMV from the nursery and to minimise the introduction of viruses in tobacco fields.

In case you cannot move the location of the nursery which was infected the previous year, it is essential to disinfect the soil and the tools by vapour, see the different Protection methods to be adopted in nursery.

Because the virus can survive in the soil for several years, crop rotations could be considered as for soil-borne diseases. Be aware in particular of the old contaminated fields , where root residues persist.

If, despite all the measures taken, some outbreaks occur after tranplanting, one can always try to eliminate the very first infected plants, in order to minimise the spread of the virus in the field, during future farming operations, especially cultivation.

Only the use of resistant varieties allows to control of the virus efficiently and permanently. Two sources of resistance are used:
- A native "variety" of Colombia, Ambalema, with a resistance governed by two recessive genes mtT1 and mt 2, its use is limited;
- Nicotiana glutinosa species which has a hypersensitivity resistance-type governed by the dominant gene Nc. This gene has shown a great stability and is still widely studied and used to create resistant genotypes. Nc can be found in virtually all types of tobacco grown. This resistance is "heat sensitive", it does not occur beyond 28-32 °

The development of molecular biology has opened up fabulous perspectives in virus control. Several strategies yielded in transformed plants with a gene coding, for example, for viral capsid protein, a satellite RNA, viral replicase ... If, in the case of TMV, such transformed tobacco genotypes have been obtained, none of them has been extensively used in the field for the time being.