Taxonomy

Economic importance

No references have been found on the economic importance of this disease.

Geographical distribution

The disease is commonly found throughout the tropics, mainly in the Caribbean and South and Central America such as in Antigua y Barbuda, Cuba, Dominican Republic, Costa Rica, French West Indies, Guyana, Panama, Peru, Puerto Rico and  Venezuela. It has  also been noted  in India, Japan, Italia, Netherlands, Antilles and  USA.

Morphology

The conidiophores form loose synnemata.  They are olivaceous brown, smooth, up to 150 µm long, 2-3 µm thick at the base, and 5-7 µm near the apex.  The conidia  are cylindrical to obclavate, conico-truncate at the base, pale olivaceous brown, with 4 - 8 septate, are 55-120 µm long and 4-8 µm thick in the broadest part.

Symptoms

Light green spots, approximately 0.5 mm in diameter, initially appear on both  surfaces of the leaf. These lesions gradually increase in size and turn brown, with yellow green border advancing at the periphery of the lesion.  About two weeks after the first appearance of the symptoms, the lesions further increase to about 3-4 mm in diameter. Two different zones are observed: the centre which is pale brown to whitish grey and the border which is brown to purple black (see figures). Although the veins limit the lesions, those which are close to each other coalesce and form blighted areas on the leaf. Severely blighted leaves turn yellow leading to defoliation.  These symptoms can be found on leaves of different ages throughout the plant, although more spots are found on older leaves.

Fruiting structures of the fungus, consisting of dark conidiophores bearing conidia, can be observed at the centre of the spots, especially after rainfall.

Differences in size, shape and colour of the spots are found. This may be due to the presence of other species of Cercospora attacking sweetpotato such as C. timorensis, and C. batatae.

The disease is dispersed by wind or splashing rain. It is most prevalent in the hot and humid tropics and is seldom observed during the dry season.

The primary host of C. bataticola is Ipomoea batatas (sweetpotato). Although no other hosts have been reported it  is suggested that this pathogen can overwinter on some weed species.

The peculiar appearance of the spots with very sharp differences between the centre and the border is one way to recognize the disease in the field.

Another way of  identifying the disease is to observe the fruiting structures under a compound microscope. For this, it is advisable to collect the samples from the field, early in the morning and to scrape the surface of the spot to observe the conidiophores and conidia.

No control measures are known. Control is not usually needed. However, it is suggested that only healthy material should be used for planting.

Differences in susceptibility have been found, but these differences could be due to the presence of other Cercospora species.

References

Ellis, M.B. 1976. More Dematiaceous Hyphomycetes. Commonwealth Mycological Institute. Surrey, England, 507 p.

Chupp, C. 1954. A monograph of the fungus genus Cercospora. Ithaca, New York; published by the author, 667 p.

De la Cruz, C.S., Loreto, F.L. and Palomar, M.K. 1981. Effect of brown leaf spot disease on the growth and yield of sweet potato. Ann. Trop. Res. 3:206-213.

Contributed by: Teresa Ames

Taxonomy

Economic importance

Geographical distribution

Morphology

Symptoms

Biology and ecology

Host range

Diagnosis

Management

References

Leaf lesions with light centres and dark margins (D. Gamarra). 

Circular spots with whitish centre and brown margin (E. Rasco, Jr.).

Characteristic spotting on leaves (T. Ames).