Genetic diversity of Bemisia tabaci species colonizing cassava in Central African Republic characterized by analysis of cytochrome c oxidase subunit I

After 2007, upsurges of whiteflies on cassava plants and high incidences of cassava diseases were observed in Central African Republic. This recent upsurge in the abundance of Bemisia tabaci (Gennadius) (Hemiptera: Aleyrodidae) was directly linked to serious damage to cassava crops resulting from spread of whitefly-borne cassava mosaic geminiviruses (CMGs). There is currently very little information describing whitefly populations on cassava and associated crops in Central African Republic. The current study aimed to address this gap, and to determine whether the increasing damage associated with B. tabaci whiteflies was the consequence of a new invasion, or an upsurge of a local population. The molecular genetic identification and phylogenetic relationships of 898 B. tabaci adult individuals collected from representative locations (54) throughout CAR were determined based on their mitochondrial cytochrome oxidase I sequences (mtCOI). Field and ecological data were also collected from each site, including whitefly abundance, CMD incidence, host plants colonized by B. tabaci and agro-ecological zone. Phylogenetic analysis of the whitefly mtCOI sequences indicated that SSA1 (-SG1, -SG2), SSA3, MED, MEAM1 and Indian Ocean (IO) putative species occur in CAR. One specific haplotype of SSA1-SG1 (SSA1-SG1-P18F5) predominated on most cassava plants and at the majority of sites. This haplotype was identical to the SSA1-SG1 Mukono8-4 (KM377961) haplotype that was recorded from Uganda but that also occurs widely in CMD pandemic-affected areas of East Africa. These results suggest that the SSA1-SG1-P18F5 haplotype occurring in CAR represents a recent invasive population, and that it is the likely cause of the increased spread and severity of CMD in CAR. Furthermore, the high mtDNA sequence diversity observed for SSA1 and its broad presence on all sites and host plants sampled suggest that this genetic group was the dominant resident species even before the arrival of this new invasive haplotype. (Résumé d'auteur

Effet De Fumures Minérales Sur Le Rendement Et La Qualité Organoleptique Du Manioc (Manihot Esculenta Crantz) Dans La Zone De Savane Au Centre-Sud De Centrafrique

Aims - The farming intensification in Sub-Saharan Africa induced soil fertility and crop yields depletion such as cassava, a main food and an important source of income of farmers in Central Africa Republic. To transcend the soil fertility depletion and improve cassava yield, LaSBAD has initiate a study focused on the mineral fertilizers of cassava crops. Methods - Four types of fertilizer were tested: the urea (Co(NH2)2), the potassium sulfate (K2SO4), the potassium chloride (KCl) and the triple superphosphate (TSP). The methodology consisted in the physical and chemical analysis of soil, the cultivation, the application of mineral fertilizers and the harvest of cassava after 12 months. Additionally, the evaluation of the organoleptic propriety of raw tubers and cassava balls after the use of fertlizers were achieved throughout semi-strucrured interviews. Results - The contribution of nitrogen and phosphorus has increased very significantly cassava yield from 18.70 to 40.20 t/ha respectively for the control treatment (T0) and the best treatment obtained (T10). A significant interaction was observed between nitrogen (N) and potassium (K) inputs on yields. The increasing doses of potassium as potassium chloride (KCl) had reduced cassava plant growth and yield. According to respondents, the organoleptic proprieties of cassava were remain quite unchangeable by mineral fertilizers. Conclusion - The application of mineral fertilizer improved cassava yield and did not affected the organoleptic quality of the raw tubers and cassava ball. Nevertheless, further studies are needed to prevent soil degradation, namely the potential use of termite nest as natural fertilizers and legumes in association or rotation with other crops

Amélioration des rendements de la culture du manioc (Manihot esculenta Crantz, Euphorbiales, Euphorbiaceae) par les terres de termitières dans la zone de savane de Damara en République Centrafricaine

The effect of termitary soil on the cassava (Manihot esculenta Crantz) crop was assessed in order to improve soil fertility and productivity of cassava in Central Africa Republic. The study focused on soil samplings and laboratory analysis of ground termitary, followed by agronomic field experiments through 12 months of cultivation using termite mounds and mineral fertilizers. Results showed that termite mounds are rich in minerals. The contribution of ground termitary and mineral fertilizer significantly increased the yield of cassava with 40.3 T.ha-1 for the treatment cassava + termite + NKP (T5) and 18.7 T.ha-1 for the control (T0). The use of mineral fertilizer combined with termitary soil (T5) generated an income of 510,000 F CFA and 630,000 F CFA higher than the control treatment (T0) evaluated at 433,000 F CFA and 490,000 F CFA, respectively after the sale of tubers/basin and bags of dried cassava by the villagers self-help group. The use of ground termitary would be a feasible method to reduce production expenses, increase yield and income of cassava producers in Central Africa Republic. Keywords: Termite mounds, Mineral fertilizer, Cassava yield, Income, Central Africa RepublicLes effets des termitières sur la culture de manioc (Manihot esculenta Crantz) ont été évalués afin d’améliorer la fertilité des sols et la productivité du manioc en Centrafrique. L’étude a porté sur l’échantillonnage des terres de termitières et de leurs analyses au laboratoire et la mise en place d’un essai agronomique pendant 12 mois de culture en utilisant les termitières et les engrais minéraux. Les résultats montrent que les termitières sont riches en éléments minéraux. L’apport des terres de termitières et des engrais minéraux, ont augmenté significativement le rendement du manioc avec 40,3 T. ha-1 pour le traitement manioc + termitière + NKP (T5) et de 18,7 T.ha-1 pour le témoin (T0). L’utilisation des engrais minéraux combinée avec la terre des termitières (T5) a généré un bénéfice de 510.000 F CFA et 630.000 F CFA supérieurs au traitement témoin (T0) qui est de 433.000 F CFA et 490.000 F CFA, respectivement après la vente des tubercules/cuvette et des sacs de cossettes du manioc, par le groupe d’entraide villageois. L’application de terre des termitières serait une méthode envisageable pour réduire les charges de production, d’augmenter le rendement et les revenus des producteurs du manioc en Centrafrique. Mots clés: Termitière, Fumures minérales, Productivité manioc, Revenu, République Centrafricain

Divergent evolutionary and epidemiological dynamics of cassava mosaic geminiviruses in Madagascar

Abstract Background Cassava mosaic disease (CMD) in Madagascar is caused by a complex of at least six African cassava mosaic geminivirus (CMG) species. This provides a rare opportunity for a comparative study of the evolutionary and epidemiological dynamics of distinct pathogenic crop-infecting viral species that coexist within the same environment. The genetic and spatial structure of CMG populations in Madagascar was studied and Bayesian phylogeographic modelling was applied to infer the origins of Madagascan CMG populations within the epidemiological context of related populations situated on mainland Africa and other south western Indian Ocean (SWIO) islands. Results The isolation and analysis of 279 DNA-A and 117 DNA-B sequences revealed the presence in Madagascar of four prevalent CMG species (South African cassava mosaic virus, SACMV; African cassava mosaic virus, ACMV; East African cassava mosaic Kenya virus, EACMKV; and East African cassava mosaic Cameroon virus, EACMCV), and of numerous CMG recombinants that have, to date, only ever been detected on this island. SACMV and ACMV, the two most prevalent viruses, displayed low degrees of genetic diversity and have most likely been introduced to the island only once. By contrast, EACMV-like CMG populations (consisting of East African cassava mosaic virus, EAMCKV, EACMCV and complex recombinants of these) were more diverse, more spatially structured, and displayed evidence of at least three independent introductions from mainland Africa. Although there were no statistically supported virus movement events between Madagascar and the other SWIO islands, at least one mainland African ACMV variant likely originated in Madagascar. Conclusions Our study highlights both the complexity of CMD in Madagascar, and the distinct evolutionary and spatial dynamics of the different viral species that collectively are associated with this disease. Given that more distinct CMG species and recombinants have been found in Madagascar than any other similarly sized region of the world, the risks of recombinant CMG variants emerging on this island are likely to be higher than elsewhere. Evidence of an epidemiological link between Madagascan and mainland African CMGs suggests that the consequences of such emergence events could reach far beyond the shores of this island

Comparative analysis of Panicum streak virus and Maize streak virus diversity, recombination patterns and phylogeography

Background: Panicum streak virus (PanSV; Family Geminiviridae; Genus Mastrevirus) is a close relative of Maize streak virus (MSV), the most serious viral threat to maize production in Africa. PanSV and MSV have the same leafhopper vector species, largely overlapping natural host ranges and similar geographical distributions across Africa and its associated Indian Ocean Islands. Unlike MSV, however, PanSV has no known economic relevance. Results: Here we report on 16 new PanSV full genome sequences sampled throughout Africa and use these together with others in public databases to reveal that PanSV and MSV populations in general share very similar patterns of genetic exchange and geographically structured diversity. A potentially important difference between the species, however, is that the movement of MSV strains throughout Africa is apparently less constrained than that of PanSV strains. Interestingly the MSV-A strain which causes maize streak disease is apparently the most mobile of all the PanSV and MSV strains investigated. Conclusion: We therefore hypothesize that the generally increased mobility of MSV relative to other closely related species such as PanSV, may have been an important evolutionary step in the eventual emergence of MSV-A as a serious agricultural pathogen. The GenBank accession numbers for the sequences reported in this paper are GQ415386-GQ415401. © 2009 Varsani et al; licensee BioMed Central Ltd

DIVERSITÉ AGROMORPHOLOGIQUE DE MANIHOT ESCULENTA CRANTZ. (EUPHORBIACEAE) CULTIVÉE DANS TROIS ZONES AGROCLIMATIQUES EN RÉPUBLIQUE CENTRAFRICAINE (RCA)

Methods.- In the goal to study agro-morphological diversity of cassavas produced by agriculturists of the Central African Republic, 179 accessions had been collected in different agro-climatic zones of the country and grew in a wood park within the forest zone (village Pissa II). 27 describers served to the analysis of the morphological diversity with the help of Community Analysis Package Version 2.15 and Canoco software. Results.- The dendrogram revealed 4 pools relatively little differentiated in relation to the extent of the morphological space between pools. There is not a real structuring between indigenous and introduced accessions. Agromorphological diversity revealed by describers doesn't correlate with the number of varieties characterized according to their vernacular names. 21 varieties high farm yield (≥ 10 Kg) were identified. There is not an interrelationship between the mean number and the middleweight of tubers harvested. Morphological features examination showed less differentiation between pools. The morphological variation range represented in a pool given of varieties is very important. Every pool preserves a big proportion of a potential morphological common. Conclusion.- Therefore, the collection is constituted with shapes and yields diversity which can constitute a good basis of selection for producers and transformers of cassava

第768回千葉医学会例会・第3回磯野外科例会 83.

List of the sequences used in the analyses. (XLSX 67 kb