Gene flow among seed plant populations.

Gene flow is a critical determinant of population genetic structure, playing an important role in both evolutionary and applied plant population genetics. Four methods have been used to estimate rates of gene flow among plant populations. I review and reconcile the data collected by these methods. The following generalization emerges: although gene flow varies substantially among species, populations, seasons, and even individual plants, at physical isolation distances of hundreds to thousands of meters, gene flow levels are frequently sufficient to counteract genetic drift and moderate levels of directional selection. This pattern suggests the genetic structure of natural plant populations is more dynamic than generally supposed. Furthermore, substantial and variable gene flow has implications for plant breeding, conservation genetics, and the potential for the escape of engineered genes. [ABSTRACT FROM AUTHOR]