The two main cultivated rice species are African rice (Oryza glaberrima) and Asian rice (Oryza sativa). They diverged genetically about a million years ago, well before their independent domestication in Africa and Asia within the last 10,000 years.

To date, scientific hypotheses have pointed to Western Africa as the place of domestication for the African variety. However, the precise location of that domestication, and how exactly it came to be, have both remained unclear.

SAHARA ARIDIFICATION

As part of France Génomique's IRIGIN program, researchers from the IRD (French National Research Institute for Sustainable Development), CEA-Genoscope (at the François Jacob Institute) and AfricaRice sought to shed light on those mysteries by studying the entire genomes of 163 domesticated and 83 wild varieties of African rice (246 genomes in all) collected in the Sahel and Eastern Africa. In so doing, they created the largest genomics database for African rice currently available and enabled an analysis of the genetic diversity of cultivated species.

With that exceptional body of data, they were able to identify the inland delta of the Niger River in Mali as the birthplace of African rice domestication and date the event to more than 3,000 years ago. Their results were coherent with archeological traces of rice domestication found in that region. 

The researchers also suggested that the domestication of African rice might have been driven by the drying of the Sahara, which would have greatly reduced the population of the wild-type rice theretofore collected by the local populations. The progressive disappearance of that resource would have led to the emergence of the cultivated form and the development of agriculture more than 2,000 years ago. 

A singular recent history

Through the analysis of the genetic data, the researchers were able to document the evolution of the wild and domesticated varieties of African rice. They illustrated the rapid expansion of African rice cultivation in the millennia following its domestication, but also the start of its decline in the 16th century, corresponding to the introduction of Asian rice in Western Africa by the Portuguese. Thereafter, numerous varieties of Asian rice, all offering higher yields, were progressively introduced and cultivated in Africa between 1870 and 1960.

Understand the past to improve the future agriculture

This study is the first to demonstrate that environmental changes have, in the past, provoked societal changes affecting the practice (domestication) and organization of agricultural systems. It also provides brainstorming material for the future of agriculture: in the current setting of global climate change (increases in temperatures, shortening of rainy seasons/overall reduction in rain, etc.) and an increasing human population, the ancestral adaptation of African rice to Sahelian-Saharan climatic conditions could be an advantage for tomorrow's rice cultures.

Indeed, in the future, the development of species less dependent on water and more resistant to high temperatures, like African rice, will be of vital interest for agriculture in Africa and the world over.

These results have been shared through a press release.