The cucumber mosaic virus ( Cucumber mosaic virus , CMV) is causing a variety of symptoms in tomato ; these are influenced in particular by the stage of development of the host, the climatic conditions, the nature of the strain prevailing and in particular the presence or absence of necrogenic satellite RNA. These symptoms are mainly localized on the foliage :
- a mottling , even a green to yellow mosaic on the young leaves (figures 1 and 2);
- deformation and reduction in the size of the leaflets (figures 2 and 3). The latter sometimes take on the appearance of fern leaves ( fernleaf ) or from time to time become very threadlike, then reduced to their veins. In this case, we speak of a “ ” shoestring aspect (figure 4). It is not uncommon to observe also deformed leaves on several stages, separated or not by leaves of normal appearance (figure 5). This clearly materializes the transient nature of the manifestation of CMV symptoms on a plant. When all the apical leaves are affected, plant growth is slowed or stopped (Figure 6). Infection results in reduced fertility and size of the fruits already forming;
- lesions , more or less confluent necrotic spots covering more or less the blade of a few leaves. These reach the petiole (figure 7), then develop on the stem in the form of longitudinal brownish streaks which can completely surround the stem (figure 8). Ultimately, the latter presents over its entire length, from the apex to the base, a generalized lethal necrosis. Before this final stage, the fruits show olive or brown annular spots and swelling (Figures 9 to 11). These necrogenic symptoms are due to certain CMV isolates that contain a necrogenic satellite RNA. There are several natural variants of the latter, which exhibit well-differentiated biological properties depending on the host. Thus, some of them (D, I17N) alleviate symptoms in tobacco, but produce generalized necrosis in tomatoes, causing very serious epidemics, especially in southern Europe and the Balkan. Others (R), on the other hand, cause symptom reduction in tomatoes as well.

Young tomato plants are more easily infected with CMV than plants that have reached the flowering stage. In addition, the earlier the infection, the greater the impact of CMV on the growth and development of the host, and hence on its yield (Figure 6). The plant early can be particularly affected stunted and bushy . Let us add that the relative proportions of the syndromes of filiformism and necrosis are very variable from one year and from one season to another. The distributions in the plots of these symptoms are different: plants affected by filiformity are distributed randomly, while those expressing necrosis form foci.