Research on coffee berry disease in Ethiopia; epidemiology and control
A. The Spread of the Coffee Berry Disease (Colletotrichum coffeanum Noack Sensu Hindorf) in Ethiopia: The rapid spread of coffee berry disease in the western and southwestern coffee producing areas of Ethiopia is closely correlated with the large-scale planting and wide distribution of the Harar variety, which is highly susceptible to the disease. As in Kenya thirty years ago, the disease is almost always first observed on trees of this variety. Men (e.g. farm workers) and animals act as vectors, and are largely responsible for the wide spatial distribution of the disease; B. Progress of the Coffee Berry Disease (Colletotrichum coffeanum) in Ethiopia: In Ethiopia, the coffee berry disease epidemic begins 84-98 days after flowering when the berries are 12-14 weeks old ad at their stage of maximum susceptibility. In susceptible varieties, e.g. Harar and Gera, there was a rapid ascent in the disease progress curve until 80 per cent of the berries are infected after which the curve approaches an asymptote. In the less susceptible varieties, disease intensity increases at a steady rate up to a maximum of 30 per cent. Significant differences in disease intensity were found in the different tree layers (subsections) and also on sides of the trees exposed in different directions. As a rule, the disease progressed more rapidly in the upper canopy than in lower parts of the tree. In the case of rapid disease progress in highly susceptible varieties, disease intensity will either be similar in all tree parts or follow a reverse pattern. Under Ethiopian conditions, disease intensity is likely to be higher on the sides of the trees exposed to the south than on the other sides. In the regression analysis, the effect of climatic factors on disease frequency is greatly underestimated, but the effect of these factors on epidemiologic development can be demonstrated by means of coincidence analyses; C. Bark and Mummified Berries as Sources of Primary inoculum of the Coffee Berry Disease in Ethiopia: All four of the Colletotrichum species known to colonize the bark of coffee trees in Kenya were found to occur in Ethiopia. However, in Ethiopia the composition of the Colletotrichum complex was found to be rather different: the proportion of C. coffeanum was remarkably high (10-20 per cent), whilst C. acutatum was isolated only in a few instances and in very small amounts (1-2 per cent). The sporulation capacity showed a bimodal distribution over the year, peaks occurring at the onset and end of the rainy season. The pathogen survives on the bark and on mummified coffee berries. During the critical period before the outbreak of the epidemic, more inoculum of C. coffeanum can be expected from twigs on the upper part of the trees than from twigs on the lower part. The number of mummies left on the trees at the beginning of the critical period has a major effect on the severity of the final attack, but not on the infection rate. Mummified berries serve as a better and more effective source of primary inoculum than the infected bark. For better control of the disease clean picking of mummified berries during the harvest is to be recommended everywhere. C. coffeanum was on two occasions isolated from the bark of the shade tree Sesbania sesban. Further hosts of C. coffeanum should therefore be sought; D. Ontogenetic Changes in the Susceptibility of the Coffee Berry to Colletotrichum coffeanum Noack Sensu Hindorf in Ethiopia: The ontogenetic susceptibility of coffee berries to Collectotrichum coffeanum reaches its maximum within 12-16 weeks after flowering. Under laboratory conditions, an infection rate > 70 per cent was achieved over a period of 17 weeks (weeks 5-22 after flowering) on coffee berry selections of the "Harar" and "Gera" varieties. Selections of the "Dilla" and "SRG" varieties showed this high susceptibility for three weeks only. In comparison with the findings in Kenya, maximum susceptibility was registered about 6 weeks later in Ethiopia. The longer period of high susceptibility of the "Harar" and "Gera" selections (as compared with the "Dilla" and "SRG" selections) together with their higher overall susceptibility explains the greater crop losses experienced with the former varieties.
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| Format: | biblioteca |
| Published: |
Eschborn (Alemania)
1979
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| Subjects: | COFFEA ARABICA, COLLETOTRICHUM COFFEANUM, DISTRIBUCION NATURAL, ENFERMEDADES FUNGOSAS, EPIDEMIOLOGIA, ESPORULACION, ETIOPIA, |
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| Summary: | A. The Spread of the Coffee Berry Disease (Colletotrichum coffeanum Noack Sensu Hindorf) in Ethiopia: The rapid spread of coffee berry disease in the western and southwestern coffee producing areas of Ethiopia is closely correlated with the large-scale planting and wide distribution of the Harar variety, which is highly susceptible to the disease. As in Kenya thirty years ago, the disease is almost always first observed on trees of this variety. Men (e.g. farm workers) and animals act as vectors, and are largely responsible for the wide spatial distribution of the disease; B. Progress of the Coffee Berry Disease (Colletotrichum coffeanum) in Ethiopia: In Ethiopia, the coffee berry disease epidemic begins 84-98 days after flowering when the berries are 12-14 weeks old ad at their stage of maximum susceptibility. In susceptible varieties, e.g. Harar and Gera, there was a rapid ascent in the disease progress curve until 80 per cent of the berries are infected after which the curve approaches an asymptote. In the less susceptible varieties, disease intensity increases at a steady rate up to a maximum of 30 per cent. Significant differences in disease intensity were found in the different tree layers (subsections) and also on sides of the trees exposed in different directions. As a rule, the disease progressed more rapidly in the upper canopy than in lower parts of the tree. In the case of rapid disease progress in highly susceptible varieties, disease intensity will either be similar in all tree parts or follow a reverse pattern. Under Ethiopian conditions, disease intensity is likely to be higher on the sides of the trees exposed to the south than on the other sides. In the regression analysis, the effect of climatic factors on disease frequency is greatly underestimated, but the effect of these factors on epidemiologic development can be demonstrated by means of coincidence analyses; C. Bark and Mummified Berries as Sources of Primary inoculum of the Coffee Berry Disease in Ethiopia: All four of the Colletotrichum species known to colonize the bark of coffee trees in Kenya were found to occur in Ethiopia. However, in Ethiopia the composition of the Colletotrichum complex was found to be rather different: the proportion of C. coffeanum was remarkably high (10-20 per cent), whilst C. acutatum was isolated only in a few instances and in very small amounts (1-2 per cent). The sporulation capacity showed a bimodal distribution over the year, peaks occurring at the onset and end of the rainy season. The pathogen survives on the bark and on mummified coffee berries. During the critical period before the outbreak of the epidemic, more inoculum of C. coffeanum can be expected from twigs on the upper part of the trees than from twigs on the lower part. The number of mummies left on the trees at the beginning of the critical period has a major effect on the severity of the final attack, but not on the infection rate. Mummified berries serve as a better and more effective source of primary inoculum than the infected bark. For better control of the disease clean picking of mummified berries during the harvest is to be recommended everywhere. C. coffeanum was on two occasions isolated from the bark of the shade tree Sesbania sesban. Further hosts of C. coffeanum should therefore be sought; D. Ontogenetic Changes in the Susceptibility of the Coffee Berry to Colletotrichum coffeanum Noack Sensu Hindorf in Ethiopia: The ontogenetic susceptibility of coffee berries to Collectotrichum coffeanum reaches its maximum within 12-16 weeks after flowering. Under laboratory conditions, an infection rate > 70 per cent was achieved over a period of 17 weeks (weeks 5-22 after flowering) on coffee berry selections of the "Harar" and "Gera" varieties. Selections of the "Dilla" and "SRG" varieties showed this high susceptibility for three weeks only. In comparison with the findings in Kenya, maximum susceptibility was registered about 6 weeks later in Ethiopia. The longer period of high susceptibility of the "Harar" and "Gera" selections (as compared with the "Dilla" and "SRG" selections) together with their higher overall susceptibility explains the greater crop losses experienced with the former varieties. |
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