Reproductive traits and molecular evidence related to the global distribution of cultivated radish (Raphanus sativus L.)

Reproductive characteristics frequently vary geographically, and reproductive success is critical for survival and local adaption in cultivated species. To document such variation in radish (Raphanus sativus L.), we examined reproductive traits and neutral genetic markers in 64 wild and landrace accessions varying in geographic origin. Flowering time tended to increase with latitude of origin, with southeastern Asian accessions (the lowest latitude) flowering earliest. Accessions from eastern Asia, which encompasses the greatest latitudinal range (18° and 54°N) of the regions we examined, exhibited the greatest variation in flowering time, clustering into a single group according to neutral genetic markers. Cluster analysis of genetic data divided the radish accessions into European and Asian groups. These groups were further subdivided into six, and two subgroups of Europe could be distinguished by root skin color. Although the accessions tended to cluster by geographic origin, those from central, southern, and western Asia clustered with both European and Asian accessions. Our results suggest that artificial selection of flowering time as well as root skin color has played important roles in local adaptation and increases in the genetic diversity of radish landraces in different geographic regions.