Main symptoms

Phytophthora capsici is an oomycete capable of attacking all organs of cucurbits.

It may be responsible for damping off seedlings in the nursery; these result in various rots affecting the hypocotyl, the crown and the first roots of the seedlings which soon wilt, collapse and gradually disappear.

On adult plants , a progressively browning wet lesion sometimes appears on the stem at soil level (Figures 1 and 2); this, once it has surrounded the stem, leads to the more or less irreversible wilting of the plants and their death. Note that the vessels underlying this lesion are more or less brown. The roots may rot, become limp, and take on a brown tint before decomposing.

The leaves touch the ground or subjected projections of contaminated soil particles (via Splash) are sometimes affected. In this case, they present spots, even more or less extensive areas, livid to yellowish, darkening, browning and necrosis quite quickly. The twigs show lesions which are also moist, dark, progressing to dark brown. Once the stem is surrounded, they induce wilting of the leaves and death of the distal part of the branch.

Moist lesions appear especially on the part of the fruits in contact with the ground (figure 3). They can sometimes be initiated elsewhere, from the peduncle and / or after contact of the fruit with other contaminated aerial organs, or following splashing occurring after rain or sprinkler irrigation. These lesions are for a fairly long time of firm consistency; they become covered from time to time with a white to grayish mycelium. Their center softens at the end of development and they quickly transform into a rot which spreads to the fruit, and leads to its more or less complete decomposition.

In addition, green fruits, such as those having reached an advanced stage of maturity, can be affected. In addition, such alterations are sometimes manifested on fruits during transport and storage.