Submitted to: Genetics
Publication Type: Peer reviewed journal
Publication Acceptance Date: 9/8/1995
Publication Date: N/A
Citation: Interpretive Summary: Cultivated sunflower had its origin from the wild annual species of sunflower. Through evolutionary time and agronomic selection, the well recognized sunflower plant has evolved. The use of classical breeding has resulted in the intercrossing of wild and cultivated sunflower. Since may desirable agronomic and economic traits have been identified in the wild species, especially genes for disease resistance, the movement of these genes into cultivated sunflower has been by interspecific hybridization. Following classical genetics, it has been assumed that the controlled crosses of wild and cultivated sunflower resulted in a mixture of the genomes from the two parents. New molecular techniques now allow us to follow the genomes in these crosses and much to our surprise these interspecific crosses are not following the strict genetic rules. There appears to be much less mixing of the two species than previously though, and less chromosomal rearrangements. It has been hypothesize that the lack of rearrangement is a mechanism to preserve the species and a prevention mechanism from cross-breeding of the different species of wild sunflowers. Armed with this knowledge and the development of newer techniques, in the future we should be able to pinpoint the desirable genes and trace their transfer from the wild species to the cultivated sunflower more efficiently.
Technical Abstract: The biological species definition of a plant is that they are reproductively isolated. Chromosomal structural differences are often viewed as important reproductive barriers, but their actual effectiveness in resisting introgression is unclear. A study was setup to trace the introgression of wild sunflower Helianthus petiolaris into cultivated sunflower Helianthus annuus. We employed 197 mapped molecular markers to study the effects of chromosomal structural differences on introgression in backcrossed progeny between karyotypically divergent species of sunflower. Forty percent of the co- linear portion of the genome introgressed, whereas only 2.4% of the genome from rearranged linkages was transferred. Thus, rather than protecting the integrity of the entire genome, chromosomal structural differences appear to resist introgression selectively, theoretically allowing maintenance of species differences in the presence of interspecific gene flow. The low frequency of introgression for many markers in the co-linear region of the genome suggests that genic factors or small undetected structural charges, as well as major chromosomal rearrangements may affect rates of introgression in Helianthus.