Evolution under domestication: contrasting functional morphology of seedlings in domesticated cassava and its closest wild relatives

Authors

  • Benoît Pujol,

    Corresponding author
    1. Department of Population Biology, Centre for Functional and Evolutionary Ecology (CEFE, UMR 5175 CNRS), 1919, route de Mende, 34293 Montpellier Cedex 05, France;
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  • Gilda Mühlen,

    1. Federal University of Rondônia, Department of Agronomy, Avenue Norte-Sul, 7300, CEP 78 987–000 Rolim de Moura, Rondônia, Brazil;
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  • Nancy Garwood,

    1. Department of Botany, the Natural History Museum, Cromwell Road, London SW7 5BD, UK;
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  • Yael Horoszowski,

    1. Department of Population Biology, Centre for Functional and Evolutionary Ecology (CEFE, UMR 5175 CNRS), 1919, route de Mende, 34293 Montpellier Cedex 05, France;
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  • Emmanuel J. P. Douzery,

    1. Institute of Evolution Sciences of Montpellier, UMR 5554 CNRS, University Montpellier II, Place Eugène Bataillon 34090 Montpellier, France
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  • Doyle McKey

    1. Department of Population Biology, Centre for Functional and Evolutionary Ecology (CEFE, UMR 5175 CNRS), 1919, route de Mende, 34293 Montpellier Cedex 05, France;
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Author for correspondence: Benoît Pujol Tel: +33 (0)4 67613299 Fax: +33 (0)4 67412138 Email: benoit.pujol@cefe.cnrs.fr

Summary

  • • Although cassava (Manihot esculenta ssp. esculenta) is asexually propagated, farmers incorporate plants from seedlings into planting stocks. These products of sex are exposed to selection, which in agricultural environments should favour rapid growth.
  • • To examine whether seedling morphology has evolved under domestication, we compared domesticated cassava, its wild progenitor (M. esculenta ssp. flabellifolia) and their sister species (M. pruinosa) under controlled conditions. Field observations complemented laboratory study.
  • • In both wild taxa, the hypocotyl did not elongate (hypogeal germination) and cotyledons remained enclosed in the testa. In domesticated cassava, the hypocotyl elongated (epigeal germination), and cotyledons emerged and became foliaceous. The difference in hypocotyl elongation was fixed, whereas cotyledon morphology varied with environmental conditions in M. pruinosa.
  • • Comparative analysis suggests that epigeal germination is primitive in Manihot, that the lineage including wild ancestors of cassava evolved hypogeal germination – which confers greater tolerance to risks in their savanna environment – and that with domestication, there was a reversion to epigeal germination and photosynthetic cotyledons, traits conferring high initial growth rates in agricultural habitats.

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