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Main symptoms


Font of seed and seedling mortality may occur in nurseries heavily contaminated with Fusarium oxysporum f. sp. melonis (figure 1).

Several leaf symptoms can appear on melon *:
- a dull green to gray-green color of the foliage;
- temporary etiolation of the apex and young leaves during the hot period of the day;
- a fairly diffuse and heterogeneous yellowing of the blade of the lower leaves, sometimes giving them the appearance of a mosaic (figure 2);
- a thinning of the veins, a more or less important sectoral (or unilateral) yellowing of the leaf blade (figures 3 to 6);
- very rapid wilting of the leaves without prior yellowing and without necrosis of the stem (symptoms caused by certain strains of race 1-2) (figure 7);
- thickening of the limbus tissues.
Eventually, many leaves, twigs and whole plants dry out and wither.

* Leaf symptoms may vary depending on the strain of F. oxysporum f. sp. melonis and the inoculum pressure, the stage of development of the plant (fruit formation, number and / or size of the latter), and the surrounding conditions (manifestation of thermal or water stress). They can be observed separately or at the same time on the same plant.

The stem initially shows a more or less discontinuous surface and unilateral browning (figure 8). Gummy exudates bead in places; they turn brown quickly as they oxidize (Figures 9 and 10). Quite quickly, a chancery, brownish necrotic damage develops several centimeters in length. Flat and localized on one side of the stem, it appears as the affected tissues dry out. At the end of the evolution, F. oxysporum f. sp. melonis may fruit on the lesions as a dense matt white to pinkish felting (Figure 11).
A longitudinal section (Figure 12) or transverse (Figure 13) in the stem shows that the vessels have a dark tint, even reddish brown to dark brown. The areas near the vascular tissues are also altered: the marrow turns brown and becomes spongy, as well as the cortical tissues (figure 14).

It should be noted that the roots located in the extension of severely damaged vessels quickly become non-functional (Figure 15). They eventually die and decompose. These root symptoms are confusing with those of other soil-borne pests, and they have led in France to wrongly associate Fusarium wilt with "root dieback".

Wet rot begins in the stalk and sometimes stylar zone of fruits (Figures 16 and 18). This symptom is less common than the foliar manifestations. A pink mold gradually covers this lesion. The vascular parasitic fungus having colonized the fruit exteriorizes on the latter. Note that melons could show symptoms after harvest.

Plants affected by Fusarium wilt are often distributed in outbreaks in the plots (Figures 19 and 20), and leaf symptoms tend to appear at the start or during cultivation although the disease can appear at all stages of plant development. often on a sector of the leaf blade or on a single branch at first (unilateral connotation of leaf symptoms). The fruits are less affected by fusarium, on the other hand they are more exposed to sun burns because of the more or less destruction of the leaf cover.

Last change : 04/30/21
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