Brown rot of citrus fruit

P. citrophthora causes citrus brown fruit rot, trunk gummosis, collar and root rot, leaf and shoot blight; symptoms vary with host and growing conditions. The fungus is reported to cause damping-off on a wide variety of nursery seedlings. The descriptions below relate to more mature plants.

On citrus, symptoms of foot rot often begin near the soil line; dark water-soaked areas form in the bark and a sour smell may occur in wet conditions. Gum exudes from the affected parts, often copiously, and is particularly noticeable in dry weather. If the diseased bark is scraped off, brown necrotic areas can been seen extending to the cambium and wood. Infections usually develop vertically more than laterally and may spread to the crown roots and upwards for 50 cm or more. The bark remains firm but as it dries out it cracks and breaks away leaving bare, dead areas. When the tree is partially girdled, decline sets in. There may be a general appearance of unthriftiness in the whole tree, with the leaves losing their colour, the foliage being sparse and the fruit small, but often the tree dies unevenly.

Leaf infection itself is usually more serious in the lower part of the canopy, appearing first as translucent spots which become necrotic. Young shoots are also attacked resulting in clumps of dead leaves. Defoliation can be severe.

Small dark spots develop on fruits near the ground which increase in size and turn various shades of greenish-brown. A soft rot (brown rot) eventually develops with a characteristic pungent odour. White mycelial growth can occur on the surface of fruit in storage.