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Main symptoms

Significant differences in symptoms are observed depending on the species or variety infected, as well as on the strain considered of watermelon ( mosaic virus Watermelon mosaic virus , WMV), which sometimes makes visual diagnosis difficult.

- In melons : Symptoms on foliage can be a more or less strong mosaic often accompanied by a dark green color along the veins (called vein-banding) and a slight twitching of the foliage (figures 1 to 3). Sometimes the symptoms are much more pronounced and there can be a dramatic reduction in the size of the leaves (Figures 4 and 5) which may not reach more than one or a few centimeters in length and be very distorted. The growth of the twigs does not appear to be affected which can give a particular appearance of a leafless twig.

In the varieties of the “Charentais” type, the symptoms of green mosaic on young fruits (Figures 6 to 8) are very spectacular, but they fade - at least partially - when they ripen, in particular in the embroidered varieties. In “Canary” type varieties, a light yellow to dark yellow mosaic is observed on the fruits.

- In cucumbers : There is a wide variety of symptoms depending on the strain of WMV and the variety cultivated. Indeed, certain strains of this virus do not cause any symptoms in this cucurbitaceae, although they multiply very well there. Other strains can, on the contrary, induce strong deforming mosaics on foliage and sometimes on fruits, and general stunting of plants.

- In zucchini : The first sign of an infection by WMV is a twitching of the leaves inward. Subsequently, the CL strains generally cause only slight mottling on the foliage and no symptoms on the fruit, which makes them practically without impact on the yield. On the other hand, EM strains most often cause strong symptoms of sometimes very deforming mosaic (filiformism, blisters). These symptoms can also be confused with those produced by Zucchini yellow mosaic virus (ZYMV). Symptoms on fruits are also often marked: Light green spots slightly depressed may appear, as well as slight deformations, which may make them unmarketable. Dark green rings or arabesques and green mosaics are observed on varieties with yellow fruits.

- In watermelon : In this species, as in cucumber or zucchini, significant variations in the expression of symptoms can be observed depending on the strain: some do not cause symptoms while others cause deforming mosaics.

Last change : 04/30/21
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