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Disease Management

Greenhouse management

Horticultural practices. To reduce infection of plants with TMV all tools should be washed with soap or a 10% solution of household bleach to inactivate the virus. TMV-contaminated soil should be discarded. To avoid transmitting the virus from an infected plant to healthy plants, the watering hose or watering can should not be allowed to make contact with the plants. Care should be taken to dispose of dead leaves and old plants, because dry, TMV-infected leaves can be blown around the greenhouse as 'dust' which can subsequently infect healthy plants if they are wounded.

Cross protection. Inoculation of a mild strain of the virus onto young plants can protect them from subsequent infection by more severe strains of TMV. This is a well documented control strategy, called "cross protection," that is successfully applied in greenhouse operations. Transgenic plants also offer alternative strategies for virus control (see Biotechnology) (Figure 11).

Figure 11

Preplanting options (greenhouse and field)

Cultivars. Several tobacco and tomato cultivars have been bred to be genetically resistant to TMV.

Biotechnology. Genetic engineering techniques have provided scientists with the ability to express the TMV coat protein gene in transgenic tobacco and tomato plants. This control strategy can safeguard the plants from infection by closely related strains of the virus (Figure 11).

Elimination of inoculum. Under experimental conditions, it has been shown that TMV can be inactivated when workers dip their contaminated hands in milk prior to planting. This inexpensive technique greatly reduces the incidence of disease (Figure 12). Seedlings that are known to be susceptible should not be transplanted into soil that contains TMV-contaminated root or plant debris.

Figure 12

Management in the field

Scouting for disease. During the growing season, infected plants should be dug up, bagged, and removed from the field. Rotation practices that include resistant plants or non host crops also should be employed to reduce the amount of inoculum in the field.

Management at harvest and in storage

TMV can easily overwinter on the seed coat, thus providing an inoculum source for the next planting cycle. Therefore, it is important to treat TMV-contaminated tobacco seed with a 10% solution of trisodium phosphate for 15 minutes. Alternatively, tomato seed contaminated with TMV can be incubated at 70°C/158°F for 2-4 days prior to planting. Both treatments will inactivate the virus that is on the seed coat, but should have little negative effect on seed germination.

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