Pollen Dispersal of Cultivated Soybean into Wild Soybean under Natural Conditions

Gene flow composed of successful seed migration and pollen dispersal strongly influences geographical population genetic structure in the self-pollinating wild soybean (Glycine soja Siebold & Zucc.). Pollen outcrossing is important in this species because it is involved in the recombination, spread, and fixation of introgressive genes and also includes the threat of introgression from genetically modified cultivated soybeans [Glycine max (L.) Merr.]. We investigated pollen dispersal in four wild soybean populations situated near farmlands using microsatellite variation. Results showed that interspecies outcrossing occurred in all four study populations. Evidence showed that some soybean individuals in wild soybean natural populations contained cultivated genes, but their genetic backgrounds tended towards wild soybean owing to many generations of gene background selection under the natural environments. A pollen dispersal distance of 40 m was found and a pollen dispersal distance of 50 m was inferred based on the morphological behaviors and geographical and population genetic structures. All the semiwild plants (Glycine gracilis Skvortsov [syn. Glycine max (L.) Merr.]) were genetically close to their mother populations, indicating that they originated in these populations through pollen flow from nearby soybeans into wild plants.