Main symptoms

Verticillium dahliae causes vascular disease which can develop early in the plant although symptoms are usually not seen until after fruit set.

On melon , affected plants frequently show slight wilting of leaves the lower at the hottest times of the day. Initially, this wilting is reversible during the night and sometimes limited to only one "side" of the plant. Subsequently, as the disease develops, it can be observed that certain sectors of the limbus, often interveinal and "V" shaped, gradually soften and turn yellow (figures 1 and 2). Large portions of the leaves eventually turn beige to brown, then necrosis and dry out (Figure 3). The leaves thus affected may die prematurely, which leads to exposure of the fruits to solar radiation and therefore to the risk of solar burns . Leaf falls were observed on melon in Tunisia.

A longitudinal or transverse cut in the vessels of the lower part of the stem , of the roots or of a branch shows that these present a fawn to slightly brown discoloration of the xylem tissues, less marked than in the case of the Fusarium wilt, and not spreading to adjacent tissues (Figures 4-6).

V. dahliae does not induce visible symptoms on the roots, no gummy exudates and lesions on the twigs, and no particular sporulation on the damaged tissues. Its symptoms are more expressed in spring and autumn in France; if they are not too advanced, the spread of the disease can stop during the summer period.