Colletotrichum kahawae
Author: Eric Newberry, University of Florida
Reviewed by: Jeffrey Rollins, University of Florida
Pathogen
Colletotrichum kahawae is responsible for coffee berry disease (CBD) on Arabica coffee (Coffea arabica). Colletotrichum kahawae, an ascomycete, has previously been confused with other Colletotrichum spp. It was originally characterized as C. coffeanum based on an isolate from Brazil where CBD does not exist. It has also been associated with the C. gloeosporioides species complex, which are weak pathogens to saprophytes of coffee berries. Colletotrichum kahawae is differentiated by its ability to cause disease on non-wounded ripe berries, morphological, phylogenetic, and biochemical characteristics (4). There are no reported hosts other than C. Arabica (1).
Symptoms and Signs
CBD causes dark, sunken lesions on green berries, which spread to cover the entire surface. These necrotic lesions cause the berry to drop prematurely. Infection hyphae colonize the interior of the fruit, leaving mummified remains. Under high humidity, pinkish, mucilaginous spores germinate in acervuli on the lesion surface. Superficial scab lesions are also observed, having concentric rings of black avervuli (1). These however do not spread to the bean (2).
Ecology and Spread
The fungus colonizes the maturing bark of coffee shoots and can infect flowers, ripe fruit, and leaves. Under conditions of high moisture and temperatures, conidia germinate and form germ tubes and appresoria when in contact with susceptible tissue. Infection hyphae arise from the appresoria and colonize the plant, creating necrotic lesions where acervuli are formed (1). Colonized bark, flowers, and mummified berries serve as sources of inoculum. The pathogen survives through the dry season on infected plant debris (2).
Rainfall is a key factor and has been positively correlated with CBD development (2). It initiates coffee berry flowering, spore germination, and infection of young berries. It also serves as a dispersal mechanism for conidia and subsequent secondary infections. High humidity is required for appresorial formation. CBD does not occur in altitudes below one thousand meters. Long distance dispersal can occur through latently infected plants, contaminated propagating material, and seed (1).
Geographic Distribution
Colletotrichum kahawae has not been reported outside of Africa or in low altitudes (1).
Management
- Plant cultivars that have shown resistance (1).
- Use cultural practices such as shading with fruit trees (2) and irrigation to induce early flowering to decrease severity (1).
- Apply fungicide treatments, although crop loses can still be high if conditions are favorable. Remember, the label is the law and the product applicator is responsible for reading and following all chemical labeling.
Diagnostic Procedures
Colletotrichum kahawae can be identified by the following morphological characteristics when grown on Malt Extract Agar:
- dark, grayish green colonies with cotton-like mycelium differentiate it from other Colletotrichum spp. (4);
- slower growth rate when compared to saprophytic species (4); and
- conidia formation directly from the hyphae with no spore masses (3).
Resources and References
1. Bailey, J. A., Jeger. M J., 1992. Colletotrichum: Biology, Pathology, and Control. CAB International.
2. Bedimo, Mouen, J. A., et al. 2010. "Role of rainfall in the development of coffee berry disease in Coffea arabica caused by Colletotrichum kahawae, in Cameroon." Plant Pathology 59(2): 324-329.
3. Manuel, L., Talhinhas, P., Várzea, V., and Neves-Martins, J. 2010. Characterization of Colletotrichum kahawae Isolates Causing Coffee Berry Disease in Angola. Journal of Phytopathology.
4. Waller, J.M., Bridge, P.D., Black, R., Hazika, G. 1993. "Characterization of the Coffee Berry Disease pathogen, Colletotrichum kahawae sp. nov". Mycological Research 97: 989–994.
