Geographic diversity cline of R gene homologs in wild populations of Solanum pimpinellifolium (Solanaceae)

Plant resistance (R) genes tend to be highly variable within plant species and are thought to be under natural selection; however, little is known about the geographic distribution of R gene diversity within and among plant populations. To determine the possible roles of demography and selection on R gene evolution, patterns of diversity at the multigenic Cf-2 R gene family were studied in Solanum pimpinellifolium populations along the northern coast of Peru. Population diversity levels of Cf-2 homologs follow a latitudinal cline, consistent with the species's history of gradual colonization of the Peruvian coast and population variation in out-crossing levels. Although previous evidence suggests that selection has shaped the DNA sequence content of the Cf-2 genes, current results imply that the geographic distribution of Cf-2 homolog diversity has been shaped primarily by demographic factors or by selective pressures with a clinal distribution.