The origins and spread of the opium poppy ( <i>Papaver somniferum</i> L.) revealed by genomics and seed morphometrics

The opium poppy (<i>Papaver somniferum</i> L.) is one of the most important plants in human history. It is the main source of opiates used as analgesic medicines or psychotropic drugs, the latter related to addiction problems, illegal trafficking and geopolitical issues. Poppyseed is also used in cooking. The prehistoric origins, domestication and cultivation spread of the opium poppy remain unresolved. Traditionally, <i>Papaver setigerum</i> has been considered the wild ancestor with early cultivation presumed to have occurred in the Western Mediterranean region, where <i>setigerum</i> is autochthonous. Other theories suggest that <i>somniferum</i> may have been introduced by Southwest Asian early farmers as a weed. To investigate these hypotheses, we analysed 190 accessions from 15 <i>Papaver</i> species using genotype-by-sequencing and geometric morphometric (GMM) techniques. Our analysis revealed that <i>setigerum</i> is the only taxa genetically close to <i>somniferum and can be better described as a subspecies</i>. The domesticated plants are, however, distinct from <i>setigerum</i>. Additionally, GMM analysis of seeds also revealed morphological differences between <i>setigerum</i> and <i>somniferum</i>. Some phenotypically wild <i>setigerum</i> accessions exhibited intermediate genetic features, suggesting introgression events. Two major populations were found in <i>somniferum</i> and, to some extent, these correspond to differences in seed form. These two populations may reflect recent attempts to breed varieties rich in opiates, as opposed to varieties used for poppyseed production. This study supports the idea that opium poppy cultivation began in the Western Mediterranean, with <i>setigerum</i> as the wild progenitor, although some wild varieties are likely to be feral forms, which can confound domestication studies.This article is part of the theme issue 'Unravelling domestication: multi-disciplinary perspectives on human and non-human relationships in the past, present and future'.