Pseudocercospora angolensis (leaf spot of Citrus spp.)

On leaves, the fungus produces circular, mostly solitary spots, which often coalesce, up to 10 mm in diameter, with a light-brown or greyish centre when dormant and non-sporulating during the dry season, but becoming black with sporulation after the onset of the rainy season (Sief and Hillocks, 1993). The lesions are usually surrounded by a dark-brown margin and a prominent yellow halo; occasionally the centre of the lesion falls out, creating a shot-hole effect. At first glance, the young lesions appear similar to those of canker (caused by Xanthomonas campestris pv. citri), but differ in being flat or shrunken. Leaf spots, especially on younger leaves, often coalesce and together cause generalized chlorosis, followed by premature abscission and defoliation of the affected tree. Young leaves and fruit appear to be more susceptible than older mature leaves (Sief and Hillocks, 1999), but whether the leaves or fruit are more affected varies with the host species and variety (Bella-Manga et al., 1999) and location (Derso, 1999).

On fruit, the spots are circular to irregular, discrete or coalescent, and mostly up to 10 mm in diameter. On young fruits, infection often results in hyperplasia, producing raised tumour-like growths surrounded by a yellow halo; these develop central necrosis and collapse (Kuate, 1998). Lesions on mature fruit are normally flat, but sometimes have a slightly sunken brown centre. Diseased fruits ripen prematurely and drop or dry up and remain on the tree (Kuate, 1998). Infection by the fungus seems to predispose the fruit to secondary infection by Colletotrichum gloeosporioides (De Carvalho and Mendes, 1952; Seif and Kungu, 1990); it is common to find a dark-brown to black sunken margin of anthracnose around the fruit spots.

Stem lesions are not frequent and mostly occur as an extension of lesions on the petiole. Occurrence of several such lesions at the stem tip results in dieback; those on other parts of the stem coalesce, become corky, and crack. At the base of the dead stem there is usually a profuse growth of secondary shoots (Menyonga, 1971).