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Main symptoms

All aerial organs of cucurbits can show symptoms of gray cloudy caused by Cladosporium cucumerinum , even at a juvenile stage in the nursery (Figure 1). The symptoms observed on species of this botanical family are often quite comparable, and one could attribute to them the following generic descriptions:

Small moist lesions appear on leaves often the youngest . These lesions gradually spread to form more or less circular spots, turning brown and necrotizing with age. They can sometimes take a grayish tint and be haloed with a more or less wide yellow halo. Affected tissue may loosen and fall, giving the inner part of the spots a more or less starry appearance, and the leaves a riddled appearance. Note that wet lesions sometimes start from veins that turn brown locally. On melon leaves (Figures 2 to 7), brown, small and necrotic spots appear. They can also be greyish, brown on the periphery, sometimes angular, surrounded by a yellow halo. Brown necrosis of the nerves also forms.

on the stems and petioles Elongated lesions develop . They are also damp at first and gradually turn brown. Their size fluctuates depending on the species and climatic conditions. Note that a viscous substance sometimes beads infected tissue. On the melon stalks (Figures 8 and 10), small beige depressed cankers are observed, in the shape of a “lip”. Over time, these cankers become elliptical, light brown, and a dark green down covers them in their central part.
Under very favorable conditions, the apices of plants may be more or less destroyed and wither away (Figures 11 and 12).

on fruits Cladosporiosis is most damaging . Small canker, greasy and concave spots, often going unnoticed, initially develop on young fruits which are particularly sensitive. They then spread, sometimes confluence, and take a circular to elongated shape and a rather light shade. Gradually browning gummy exudates locally bead. Note that these spots are initially harmless on the young fruits of Cucurbitaceae; as development progresses, they have very important repercussions on their shape in particular. Indeed, their extension and the local establishment of corky scar tissue in relief sometimes lead to bursts and significant deformations, making the fruits unmarketable.
On melons (figures 13 to 21), the spots, small and oily at first on young melons, extend, lengthen, and locally suberise. Fruiting of bodies C. cucumerinum form in the center of the spots and give them a dark green to black color.

A gray to dark green conidial felting and more or less dense covers the diseased tissues of all the organs attacked. It is particularly visible on lesions on stems (Figures 10 and 12) and on fruits (Figures 16, 17, 19, 21).

Last change : 04/30/21
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