HARTER, A.V.*, ALLEN HWANG, and LOREN H. RIESEBERG. Department of Biology, Indiana University, Bloomington IN 47405. - A microsatellite investigation into the origin(s) of cultivated sunflowers.
Although the Helianthus species most closely related to the
cultivated sunflower is known to be the widespread Helianthus annuus,
the geographic origin(s) of the cultivated sunflower is still unresolved.
We have used nine microsatellite loci to investigate the relationships
among 12 geographically diverse populations of H. annuus and 11
strains of cultivated sunflowers including both commercial lines and Native
American-developed strains from Mexico and the United States. Our analyses
of wild populations of H. annuus have revealed high levels of gene
flow among populations throughout its geographic range and high levels of
genetic diversity in all populations. In contrast, the cultivars exhibit a
range of genetic diversity from almost monotypic at all loci examined to
diversity indices nearly comparable to wild populations. A global Analysis
of Molecular Variance (AMOVA) of all wild and cultivated populations
revealed 72% of the variance was accounted for by differences within
populations. Conversely, only 10% of the variance was explained by the
differences between cultivated and wild H. annuus. There was
considerably greater variance among individual cultivated populations than
between cultivated and wild populations. This observation suggests multiple
origins for the cultivated sunflower. Among the cultivars, only three
strains showed strong genetic relatedness to each other: two Native
American strains and the Mammoth commercial line. The latter of these was
re-introduced to the United States from Russia in the late 19th century.
Thus, it appears to have originated from cultivars developed by Native
Americans in the east-central United States. Although some relationships
were observed between cultivated strains and geographic regions, the exact
genetic relationships between specific wild populations and specific
cultivated strains were difficult to determine due to the high level of
gene flow and genetic diversity in the wild populations.
Key words: domestication, gene flow, Helianthus annuus, microsatellite, sunflower