Main symptoms

As with TMV , the symptoms caused by Tomato mosaic virus (ToMV) are very varied and are quite comparable. In addition to causing a slowdown in growth plant , various coloring anomalies may appear on the leaflets and leaves : thinning of the veins, marbling, a more or less contrasting mosaic, in green, yellow or even white areas ( aucuba) (Figures 1 and 2). The blade is also more or less embossed and tightened. As with TMV, the leaflets and leaves are threadlike in winter conditions, due to a lack of light in plants grown in shelters.

We can also see the fall of flowers . The fruits , when ripe, are small and sometimes more or less bumpy. They also undergo yellow discolorations (Figure 3), sometimes in rings, as well as internal necrotic changes localized in the vascular tissues ( Internal browning ). These symptoms can be present on green or mature fruits when the plant is healthy in appearance. The earlier the attacks, the more impact they have on yields; late infections are of no consequence for production.
Given the mode of transmission of this virus (by contact), the distribution of diseased plants in the crop is often in line, especially when the infections are linked to cultivation operations carried out by following the rows. Note that generally, symptoms can vary in intensity depending on the strain, cultivar, stage of infection, temperature, light intensity, nitrogen and boron content in the soil. Thus, the high temperatures contribute to an alleviation of leaf symptoms. Conversely, tomato varieties possessing the “ Tm2 ” or “ ” Tm2 genes ² can produce, under high temperature conditions, necrotic reactions in the presence of common strains of ToMV and TMV.

The mixed infections between ToMV and other viruses are very common, especially with CMV, PVY In this case, the symptoms are often more severe. Let us recall, by way of example, the ToMV-PVX co-infection leading to the appearance of the serious symptom called by the Anglo-Saxons “double streak”.