PLoS ONE (2011) 6(5): e19563

DOI:10.1371/journal.pone.0019563

Selection for earlier flowering crop associated with climatic variations in the Sahel

Yves Vigouroux1,2, Cédric Mariac1,2, Stéphane De Mita1, Jean-Louis Pham1, Bruno Gérard3, Issoufou Kapran4, Fabrice Sagnard5, Monique Deu5, Jacques Chantereau5, Abdou Ali6, Jupiter Ndjeunga3, Viviane Luong1, Anne-Céline Thuillet1, Abdoul-Aziz Saïdou1,2,7, Gilles Bezançon2

1Institut de Recherche pour le Développement, Montpellier, France, 2Institut de Recherche pour le Développement, Niamey, Niger, 3International Center of Research for the Semi-Arid Tropics, Niamey, Niger, 4Institut National de la Recherche Agronomique du Niger, Niamey, Niger, 5Centre de Coopération Internationale en Recherche Agronomique pour le Développement, Montpellier, France, 6Centre Régional AGHRYMET, Niamey, Niger, 7Université Abdou Moumouni, Niamey, Niger

Abstract
Climate changes will have an impact on food production and will require costly adaptive responses. Adapting to a changing
environment will be particularly challenging in sub-Saharan Africa where climate change is expected to have a major
impact. However, one important phenomenon that is often overlooked and is poorly documented is the ability of agrosystems
to rapidly adapt to environmental variations. Such an adaptation could proceed by the adoption of new varieties or
by the adaptation of varieties to a changing environment. In this study, we analyzed these two processes in one of the
driest agro-ecosystems in Africa, the Sahel. We performed a detailed study in Niger where pearl millet is the main crop and
covers 65% of the cultivated area. To assess how the agro-system is responding to recent recurrent drought, we analyzed
samples of pearl millet landraces collected in the same villages in 1976 and 2003 throughout the entire cultivated area of
Niger. We studied phenological and morphological differences in the 1976 and 2003 collections by comparing them over
three cropping seasons in a common garden experiment. We found no major changes in the main cultivated varieties or in
their genetic diversity. However, we observed a significant shift in adaptive traits. Compared to the 1976 samples, samples
collected in 2003 displayed a shorter lifecycle, and a reduction in plant and spike size. We also found that an early flowering
allele at the PHYC locus increased in frequency between 1976 and 2003. The increase exceeded the effect of drift and
sampling, suggesting a direct effect of selection for earliness on this gene. We conclude that recurrent drought can lead to
selection for earlier flowering in a major Sahelian crop. Surprisingly, these results suggest that diffusion of crop varieties is
not the main driver of short term adaptation to climatic variation.

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Comptes Rendus Biologies (2011) - Article in Press

DOI:10.1016/j.crvi.2011.03.003

Biodiversity, evolution and adaptation of cultivated crops

Yves Vigouroux, Adeline Barnaud, Nora Scarcelli, Anne-Céline Thuillet
Institut de recherche pour le développement (IRD), Montpellier, France

Abstract
The human diet depends on very few crops. Current diversity in these crops is the result of a long interaction between farmers and cultivated plants, and their environment. Man largely shaped crop biodiversity from the domestication period 12,000 B.P. to the development of improved varieties during the last century. We illustrate this process through a detailed analysis of the domestication and early diffusion of maize. In smallholder agricultural systems, farmers still have a major impact on cropdiversity today. We review several examples of the major impact of man on current diversity. Finally, biodiversity is considered to be an asset for adaptation to current environmental changes. We describe the evolution of pearl millet in West Africa, where average rainfall has decreased over the last forty years. Diversity in cultivated varieties has certainly helped this crop to adapt to climate variation.