The role of introgression in plant evolution has been the subject of intense interest and speculation for over fifty years. Introgression is the transfer of genes from one species to another through hybridization and repeated backcrossing. The classic examples of introgression have used morphological features as evidence of this process. Because of difficulties interpreting morphological data in terms of specific genes, these studies have provided only tentative estimates of the significance of introgression as an evolutionary mechanism in plants. Dr. Loren Rieseberg will apply powerful new molecular methods of protein and DNA analyses to measure gene flow among populations and species of presumptively hybridizing plants. The annual species of sunflower, Helianthus, are an ideal group for studying introgression because of the extensive morphological and cytological data base already available for these plants. Furthermore, evolutionists frequently cite members of this group as outstanding examples of introgression. The objectives of Dr. Rieseberg's project are: 1) to determine the significance of introgression among the annual sunflowers using protein (allozyme) and DNA evidence; 2) to construct a DNA-based phylogeny for the 11 species of section Helianthus; and 3) to establish a general methodology for the molecular analysis of introgression in plants.
