A strategy for durable resistance to and efficient control of Colletotrichum kahawae in Arabica coffee in Cameroon
Arabica coffee berry disease (CBD) caused by C. kahawae is one of the major factors limiting Arabica coffee production in Africa. Losses recorded in Cameroon are around 50 percent on average. Currently, the main objective for controlling this disease is tosearch for, create and disseminate varieties with sustainable resistance to CBD, which are adapted to the different ecologies and farming practices employed in the field. To that end, greater knowledge of pathogen populations, the nature and degree of resistance in the host germplasm, and various epidemiological parameters of the disease is required. The genetic diversity of pathogen populations in Cameroon was assessed by determining vegetative compatibility groups (VCG), and subsequently compared to that in East African countries, using RAPD markers. Host-parasite relationships were characterized by artificially inoculating the hypocotyls of uprooted seedlings and unripe berries taken from Arabica coffee trees. The effect of certain abiotic factors on disease incidence was measured. Primary inoculum sources were sought. A single vegetative compatibility group (VCG) was detected in Cameroon population. A structural analysis of the Cameroonian population by RAPD suggested that this population was clonal with a limited structure. A comparison with the population from East Africa revealed one VCG comprising two subgroups (East Africa and Cameroon) and the existence of substantial genetic differentiation between the two geographical populations, which suggested that there was no pathogen migration between these two regions and raised the problem of where the disease originated and how the pathogen evolved. Pathogenicity tests carried out with the different isolates studied did not reveal any specific resistance reactions. Nevertheless, various levels of isolate aggressiveness and different levels of resistance between genotypes were observed. Arabica coffee tree resistance seemed to be non-specific. The two resistance assessment methods usable in the laboratory showed that the genetic base of the tested accessions was narrow. The results obtained on hypocotyls seemed to be more reliable than those obtained on berries. However, the method most representative of tree performance in the field under high parasite pressure remains to be identified. The role of climate in development of disease was clearly established. However, the effect of each abiotic factor on disease development, for each farming system, remains to be determined. The investigation carried out into primary inoculum sources revealed that leaves and twigs bearing fruiting nodes are capable of harbouring the fungus. Nevertheless, it is still not known how this inoculum is conserved. Given the knowledge already acquired, an effective control method based on general and sustainable resistance and environmental management can be envisaged.
| Main Authors: | , , , , , , |
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| Format: | biblioteca |
| Published: |
Trieste (Italia) ASIC
2001
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| Subjects: | AFRICA, AFRICA ORIENTAL, BIODIVERSIDAD, CAMERUN, CLIMA, COFFEA ARABICA, COLLETOTRICHUM, CONTROL DE ENFERMEDADES, FACTORES CLIMATICOS, FRUTAS, GENETICA DE POBLACIONES, GENOTIPOS, GERMOPLASMA, HIPOCOTILOS, HOJAS, MARCADORES GENETICOS, ORGANISMOS PATOGENOS, PATOGENICIDAD, PLANTULAS, RECURSOS GENETICOS, RELACIONES HUESPED PARASITO, RESISTENCIA A LA ENFERMEDAD, VARIACION GENETICA, |
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