Protection Methods

- During cultivation

Unlike fungal diseases, there is no curative method to effectively control viruses and particularly cucumber mosaic virus (CMV) during cultivation. Generally, an infected plant will remain infected all its lifecycle, although symptoms may sometimes diminish.

If the infections occur in nurseries and are detected early, the plants showing CMV symptoms should be quickly eliminated (figure 1) and in no case be transplanted later.

Aphicide treatments are necessary to control aphid populations on tobacco. Unfortunately, they are often ineffective for controlling virus outbreaks. The reason is that  aphids often come from outside the field and transmit the virus during brief punctures, frequently before the aphicide has time to act. Moreover, the current difficulties in controlling aphids on tobacco, are sometimes linked to insecticide resistance. This resistance  does not improve the situation of CMV control.


- Next crop

A set of measures should be implemented in order to prevent or at least minimise the introduction of viruses in tobacco fields.

In countries where early contaminations occur, it is necessary to protect nurseries and young plants. For this reason, one may use agrotextiles (unwoven fabrics, mesh ...). The mechanical barrier does not allow further contamination.

Careful weeding of nurseries (figure 3), fields and their surroundings (borders, hedges and paths) should be conducted to eliminate virus sources and / or vectors. Avoid setting a tobacco crop next to CMV susceptible crops, such as tomato, spinach, cucurbits ...

In general there is no CMV resistant tobacco variety. The selection of such varieties is not easy. However, a breeding program was undertaken in Taiwan, using a resistant parent developed in the United States: TI 245. Partial resistance conferred by the presence of seven genes, that result in a reduction of infestation rate. Another more efficient source of resistance  has previously been described in a variety of Indian tobacco, but it has never been used. Several other genotypes of tobacco with different levels of resistance to CMV have been reported in Japan.

The development of molecular biology has opened fabulous perspectives in virus control. Several strategies have been developed. These strategies yielded in transformed plants with a viral gene coding for example for capsid protein, a satellite RNA, or viral replicase. Some of these strategies that have been tested in China on a large scale, have shown a significant efficiency, namely in tobacco.