Epidémiologie, diversité génétique, distribution et contrôle des virus de la mosaïque africaine du manioc et de son vecteur (Bemisia tabaci) dans la région du Sud-Kivu en République Démocratique du Congo
(2012)
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- Supervisors
- Bragard, Claude
- Abstract
- (en) An assessment of the epidemiology of cassava pests and diseases in the South Kivu region of the D.R. Congo, and of the molecular diagnosis of cassava mosaic viruses based on their AC2 and AC4 genes, showed that there is a high disease prevalence in the low-altitude areas where cassava is grown intensively. Two virus species (African cassava mosaic virus, ACMV, and East African cassava mosaic virus, EACMV) occur in this region both in cassava plants and in their whitefly vectors (Bemisia tabaci), resulting in severe symptoms and major yield losses. These losses were higher in low-altitude areas where EACMV-UG alone, or in a dual infection with ACMV, was frequent. The incidence of cassava mosaic disease (CMD) ranged from 65 to 100% in low-altitude areas and from 9.5 to 77.7% in high altitude ones. The number of whiteflies per leaf was 8-17.9 and 1-11.3, respectively. The disease severity scores reflected these differences. Based on a phylogenetic study of the partial sequences of their DNA A genome, the ACMV isolates clustered into five distinct groups, whereas the EACMV-UG isolates fell into only two groups, probably due to their more recent history in the region. The whitefly population, which was studied using the sequences of Cytochrome oxydase I of the mitochondrial gene (mtCOI), was homogenous independently of its host plants. Among the 10 major local cassava varieties and five improved genotypes studied, two local varieties (Pharmakina and Cizinduka) and three improved genotypes (MM96/002, MM96/157, MM96/6967) were the most productive and the most tolerant of the disease. The cultivation of cassava in an intercropping system resulted in a reduction of 19% and 33.3% in disease incidence and its vector population, respectively. The study highlighted the differential distribution and impact of cassava mosaic disease depending upon agro-ecosystem characteristics, with factors such as altitude, genotype, virus species and infection period playing a role in the disease epidemic. Under conducive conditions, yield losses ranging from 77.5 to 97.3% have been recorded. Our results indicate that CMD management needs to be considered as more complex than simply managing a viral disease. We propose that an integrative approach should be adopted, taking into account the agro-ecosystem in which cassava is grown, the type of cropping system, varietal adaptation and vector presence and distribution, as well as the incidence of other endemic cassava pests and diseases. It is also very important to ensure the availability of disease-free cassava cuttings and well-adapted cassava varieties.
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Citations
Bisimwa Basengere, E. (2012). Epidémiologie, diversité génétique, distribution et contrôle des virus de la mosaïque africaine du manioc et de son vecteur (Bemisia tabaci) dans la région du Sud-Kivu en République Démocratique du Congo. https://hdl.handle.net/2078.5/38651