Cocoa pods, Venezuela. Photo: C.Lanaud ©CIRAD
Arabica coffee, Ethiopia. Photo: ©Jean-Pierre Labouisse
Yams in Benin. Photo: J-L Pham ©IRD
Rice harvest, Guinea. Photo: J-L Pham ©IRD
Maize corn. Photo: ©Brigitte Gouesnard

Main results

Crop studies

Temporal dynamic of Oryza glaberrina varietal diversity in West Africa

Survey results from the Cascades region of Burkina Faso indicate drastic change in the statute of O. glaberrima varieties, from the dominant position in the 1960s to an extremely marginal position nowadays. Survey results from Maritime Guinea, indicate contrasted dynamics. In general O. glaberrima is perceived as the «economical rice for large (and somehow poor) families» whereas O. sativa is «the sweet and sugared rice that people prefer».

Maize diversity in Burkina Faso

The impact of modern varieties: Nuclear and cytoplasmic DNA analyzes showed a weak structure between maize landraces. Comparison between landraces and modern varieties suggested gene flow between the two types. The most anciently released modern varieties were likely creolized. Despite the influence of modern varieties, allelic richness of landraces was still high. Genetic erosion will become a risk if farmers start to grow, near their local populations, a limited number of modern varieties with a narrow genetic base. It is time to collect the landraces in order to preserve their diversity as guaranty of genetic progress.

Durum wheat diversity in Morocco

The genetic differentiation between the two regions was high. The adoption of modern varieties differs in the Pre-Rif region and in the High Atlas, where they may have been “creolized”. Inside a region, a given name most often included different genotypes, and reciprocally, a given genotype could correspond to different names. We found some primitive domesticated wheat (ssp. dicoccum) phenotypes in the populations; however, their genetic diversity indicates that they are a part of the cultivated compartment.  

Uneven distribution of the crop species and sorghum varieties among neighborhood groups

No significant relation was found between the household species richness and the clan or age class of the household head, whereas a significant relation was found with the ntora (neighborhood-groups).

Uneven distribution sorghum varieties and their genetic diversity among ethnic groups:

14 different varieties were respectively inventoried in the Chuka and Tharaka groups, and 10 in the Mbeere group. The results showed that sorghum variety assemblages differed significantly between ethnic groups, even though the ethnic partition explained a limited part of variability. The genetic diversity of sorghum in the area of study, as assessed with molecular markers, is organized in four major groups. These groups reflected the influence of improved variety dissemination and a differentiation in terms of cycle duration and phenology. As a result of the unbalanced frequency of the different genetic clusters across ethnic groups, the genetic differentiation of their sorghum populations was significant.

Transversal approach combining social and biological sciences

A common protocol was implemented in Burkina Faso, Guinea, Kenya and Morocco, in order to characterize trends in the crop and varietal dynamics of cropping systems reflecting various agroecological and economic conditions. For a total of 1412 farmers, 932 men and 480 women, were interviewed in Burkina Faso (100), Guinea (840), Kenya (208) and Morocco (264). Across the countries, 208 villages were visited. Farmers belong to 56 different ethnic groups. The number of crops cultivated per farmer is 4.8 in Morocco, 5.2 in Kenya, 6.6 in Burkina Faso and 6.9 in Guinea. Each study site has its specific crops. Fonio is mainly cultivated in Guinea and durum wheat in Morocco, while groundnut is cultivated by less than 20% of farmers. Sorghum is usual in all countries, except Morocco. Considering all surveyed sites, farmers have cultivated 6.8 crops along their life on average.  The average number of crops still cultivated today is 6.4 crops per farmer. The number of abandoned species increases from 2000, but this result must be weighted by the number of farmers to be interpretable.

Integration with worldwide and regional data

Pearl Millet: Genetic diversity and domestication process in Central and West Africa

 Diversity hotspots were found in the southern limit of wild population distribution. As expected, lower genetic diversity was observed in the cultivated varieties as compared to the wild populations. However, an unexpected result is that wild population diversity was positively correlated with cultivated introgression. The discovery that wild diversity is enhanced by cultivated gene flow calls into question the widely held assumption that cultivated gene flow is only detrimental to wild populations.

Sorghum: Genetic diversity and domestication process in West Africa

A preliminary analysis combining all the cultivated accessions collected in Burkina Faso, Guinea, Mali and Niger (1605 accessions) and genotyped with 28 SSRs indicated a contrasted pattern of genetic diversity among countries. Sorghums from Burkina Faso and Guinea are the least diverse in terms of both unbiased gene diversity and allelic richness compared to Mali and Niger in which greater racial sorghum diversity was observed. Our analyses confirm that sorghum genetic diversity seems to be associated with the botanical diversity. In Guinea, the distribution of genetic diversity within the “guinea margariferum” types appeared to be associated with both environmental and ethnical factors at the country scale. At a finer scale, the Malinké people cultivate two types of “guinea margaritiferum”, which were suspected to be associated with different climatic patterns.
The Neighbour joining tree indicated that sorghum from Burkina Faso clustered in one major group composed by accessions classified as “guinea” types (not margaritiferum), based on their panicle and spikelet morphology., Accessions from Niger and Mali were dispersed all over the tree as expected. The “guinea margaritiferum” collected in Mali seemed to represent only a part of the diversity detected in Guinea for this group of sorghum. The Malian “guinea margaritiferum” types were closely associated with one cluster detected in Guinea: the cluster of “guinea margariferum” specific of the Malinke people. Our results probably indicate a common origin for these types.

Rice: Transcriptomic and genomic sequencing to develop new resources

A reference set of 300 O. glaberrima and 100 O. barthii accessions representative of the geographical diversity was selected and genotyped. The O. barthii populations are structured on a geographical origin basis. The main diversity observed in this survey was lying in the Lake Chad area.The O. glaberrima accessions showed a much lower diversity with no clear geographically structured distribution of the genetic diversity. The results suggest a strict maintenance of the genetic isolation between the two species since the O. sativa introduction in West Africa.

Maize: origin of Burkinabe landraces based on nuclear SSR

The admixture rate of Burkinabe landraces was high. A few landraces were grouped with the Italian cluster, the other derived from Mexican and Caribbean clusters and to a lesser extent from Andean and Corn Belt Dent clusters. Litterature suggest two ways of introduction ways (Mediterranean, Egypt and the Nile; the Guinean gulf), and that two main clusters contributed to West African landraces: middle South-America, Northern South-America.Because the Nile origin does not seem to be retained in the recent publications, we will reanalyze our data by comparison with the American continent only

  • Maize: contribution of cytoplasmic analysis to the structuration of American, European and African maize landraces: Our study on cytoplasmic markers confirms the multiple ways of introduction of maize in Africa and the low structuration of the diversity. 
  • Transferring methodologies to underutilized crops to assess crop genetic diversity and adaptation:

Fonio remains largely under-studied compared to other African cereals such as sorghum, millet and rice. During the frame of Arcad SP3 project, 38 nSSR markers, chloroplast sequences and 12 cpSSR markers were released and new genetic resources are developed. We have genotyped the largest collection available for fonio. We have also conducted genetic diversity studies at the country scale in Guinea, Senegal and Niger. Finally we are documenting fonio domestication process through phylogenetic and phylogeographic approaches of African Digitarias.Preliminary results show that reproductive system is most probably autogamous and that genetic diversity observed in Guinea is large compared to other countries, confirming the common idea that Guinea could be a/the white fonio center or origin.

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