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Pseudocercospora fruit and leaf spot
[Fungus] Pseudocercospora angolensis (T. Carvalho & O. Mendes) Crous & U. Braun 2003
Originally Cercospora angolensis, Phaeoisariopsis sp., Pseudo phaeoramularia, Phaeoramularia angolensis
Other common names
Phaeoramularia fruit and leaf spot (PFLS), Angular leaf spot of Citrus
Pseudocercospora angolensis is a fungus that requires moisture for infection and the production of wind-borne conidia. Other than by wind, conidia can be transported on infected fruit or propagative material. Local dispersal is primarily by rain-splash or raindrops. Humans mediate in the dissemination of the fungus through transport of infected plant material and/or fruits from infected areas. Because leaf lesions produce more conidia than similar lesions on fruit, it is more likely that they constitute the main source of infection during disease spread in infected areas.
The fungus probably survives in dormant lesions on infected material until the onset of conditions is conducive to sporulation.
The disease is favored by prolonged wet weather that stimulates the production of new susceptible flush. Lesions produced the previous season can begin to sporulate within two weeks of the beginning of the rainy season, at most temperatures in the tropics, and those spores infect the new tissue.
Leaf - the fungus produces circular, mostly solitary spots up to 10 mm in diameter, which often coalesce. Lesions have light brown or grayish centers when dormant and are non-sporulating during the dry season, but becoming black with sporulation after the onset of the rainy season. The lesions are usually surrounded by a dark brown margin and a prominent yellow halo; occasionally the centre of the lesions falls out, creating a shot-hole effect. At first glance the young lesions appear similar to those of canker (caused by Xanthomonas citri spp.-pv citri) but differ in being flat or shrunken. Leaf spots, especially on younger leaves, often coalesce and cause generalized chlorosis, followed by premature abscission and defoliation of the affected tree. Yound leaves and fruit appear to be more susceptible than older mature leaves, but whether the leaves or fruit are more affected varies with the hose species, variety, and location.
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 tumor-like growths surrounded by a yellow halo; these develop central necrosis and collapse. Lesions on mature fruit are normally flat but sometimes have a slightly sunken brown centre. Diseased fruits ripen prematurely and drop (can be significant) or dry up and remain on the tree. Infection by the fungus seems to predispose the fruit to secondary infection by Colletotrichum gloeosporioides; it is common to find a dark-brown to black sunken margin of anthracnose around the fruit spots.
Stem - 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.
Citrus spp. (Rutaceae); the disease has been observed on all citrus species, including grapefruit, lemon, lime, orange, pummelo, and mandarin. Grapefruit, orange, pummelo, and mandarin are very susceptible, lemon is less susceptible, and lime is the least susceptible.
Africa (in the humid tropics), Comoros Islands, and Asia (Yemen)
Easily confused with
At an early stage, the lesions caused by Pseudocercospora angolensis on leaves appear similar to those of citrus canker caused by bacterium Xanthomonas citri spp. citri (Hasse) Dye. They differ in being flat or shrunken, rather than raised. Canker lesions on leaves also have a yellow halo, but are distinguished by a water-soaked margin around the spot, as are the flat lesions caused by other bacterial pathogens of citrus.
The fungus Guignardia citricarpa Kiely also causes spots on leaves and/or fruits of citrus in Africa, Asia, Australia, and South America, but leaf lesions are uncommon. The lesions of the disease called "black spot" may resemble those produced by P. angolensis, particularly on lemon leaves. Small, globose, black fungal pycnidia containing single-celled colorless spores often are produced in these spots.
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