title: Geographic differences in patterns of genetic differentiation among bitter and sweet manioc (Manihot esculenta subsp. esculenta; Euphorbiaceae).
abstract: OBJECTIVE
  Manioc (Manihot esculenta subsp. esculenta), one of the most important tropical food crops, is commonly divided according to cyanide content into two use-categories, "sweet" and "bitter." While bitter and sweet varieties are genetically differentiated at the local scale, whether this differentiation is consistent across continents is yet unknown. •
  
  
  METHODS
  Using eight microsatellite loci, we genotyped 522 manioc samples (135 bitter and 387 sweet) from Ecuador, French Guiana, Cameroon, Gabon, Ghana, and Vanuatu. Genetic differentiation between use-categories was assessed using double principal coordinate analyses (DPCoA) with multivariate analysis of variance (MANOVA) and Jost's measure of estimated differentiation (D(est)). Genetic structure was analyzed using Bayesian clustering analysis. •
  
  
  RESULTS
  Manioc neutral genetic diversity was high in all sampled regions. Sweet and bitter manioc landraces are differentiated in South America but not in Africa. Correspondingly, bitter and sweet manioc samples share a higher proportion of neutral alleles in Africa than in South America. We also found seven clones classified by some farmers as sweet and by others as bitter. •
  
  
  CONCLUSIONS
  Lack of differentiation in Africa is most likely due to postintroduction hybridization between bitter and sweet manioc. Inconsistent transfer from South America to Africa of ethnobotanical knowledge surrounding use-category management may contribute to increased hybridization in Africa. Investigating this issue requires more data on the variation in cyanogenesis in roots within and among manioc populations and how manioc diversity is managed on the farm.
authors.affiliation: University of Wisconsin-Madison, Botany Department/Birge Hall, 430 Lincoln Drive, Madison, WI 53706-1381, USA. ebradbury@wisc.edu
authors.forename: E Jane
authors.initials: EJ
authors.lastname: Bradbury
authors.forename: Anne
authors.initials: A
authors.lastname: Duputié
authors.forename: Marc
authors.initials: M
authors.lastname: Delêtre
authors.forename: Caroline
authors.initials: C
authors.lastname: Roullier
authors.forename: Alexandra
authors.initials: A
authors.lastname: Narváez-Trujillo
authors.forename: Joseph A
authors.initials: JA
authors.lastname: Manu-Aduening
authors.forename: Eve
authors.initials: E
authors.lastname: Emshwiller
authors.forename: Doyle
authors.initials: D
authors.lastname: McKey
mesh_terms: D000349:Africa; D003710:Demography; D014644:Genetic Variation; D002365:Manihot / Q000235:genetics*; D058974:Phylogeography; D013020:South America
keywords: Euphorbiaceae; cassava; crop management; crop migration; cyanogenesis; domestication; microsatellite loci; population structure; small-holder agriculture