Submitted to: Helia
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/2/2009
Publication Date: 7/1/2009
Citation: Presotto, A., Cantamutto, M., Poverene, M., Seiler, G. 2009. Phenotypic Diversity in Wild Helianthus annuus from Argentina. Helia. 32(50):37-50.
Interpretive Summary: Wild annual sunflower is native to North America, where it is widely distributed. This species has become naturalized in central Argentina being distributed over an area of about 12 million acres. Since its establishment 60 years ago, it has continuously increased in area, behaving as an invasive species, providing evidence that it will continue to spread. This species is a potentially valuable germplasm resource for cultivated sunflower. No studies have been done to characterize the naturalized wild annual sunflower populations in Argentina and to assess the genetic diversity of these populations compared to the populations from the center of origin in North America. The wild annual sunflowers used in the study were from nine representative populations from different geographic regions of Argentina and 17 populations from 17 states of the USA, grown in a common garden in Argentina. Populations of wild annual sunflower naturalized in Argentina showed a profound phenotypic similarity with the 17 wild populations from the center of origin in North America. The populations naturalized in Argentina presented a high degree of phenotypic variability. However, variability was lower than that in populations examined from North America, but was sufficient to differentiate among populations from both continents. The phenotypic descriptors were useful to differentiate the Argentine populations and to confirm their wild origin from the North America populations. The wild annual populations from Argentina and North America showed the presence of some characteristics that would indicate introgression with the cultivated sunflower. At present, it is not possible to clearly differentiate the North American introgressed populations from the Argentine ones. The Argentine populations would not have introgressed traits from cultivated sunflower to the extent of those from the center of origin in North America due to the shorter period of time that they have been in contact with the cultivated crop. The naturalized wild Helianthus annuus populations established in Argentina represent new biodiversity and a potentially useful genetic resource for broadening the narrow genetic base of cultivated sunflower.
Technical Abstract: Wild Helianthus annuus populations naturalized in central Argentina have spread since their introduction from the center of origin in North America. Phenotypic characterization based on 45 morphological and phenological descriptors of nine populations from different geographic regions of Argentina and 17 populations from the USA provided by the U.S. Department of Agriculture, Agricultural Research Service wild sunflower germplasm bank at Ames, Iowa, USA was obtained by growing populations in a common garden. Wild populations from Argentina reflected part of the phenotypic variability of populations from the center of origin, but showed adaptation to local conditions that allowed differentiation between populations from each continent. All traits showed a continuous range with the majority of extreme values in populations from North America. The populations that showed similarities for one group of descriptors differed by other traits, revealing the existence of different phenotypes. Helianthus annuus populations established in Argentina could be considered a differentiated genetic resource, containing new combinations and traits absent in North American populations, such as life cycle length in the Diamante population of 180 days and longer, the longest of any population studied.