|Di Bernardo, N|
|Della Casa, S|
Submitted to: Helia
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/15/2004
Publication Date: 8/14/2004
Citation: Vischi, M., Di Bernardo, N., Scotti, I., Della Casa, S., Seiler, G., Olivieri, A.M. 2004. Comparison of populations of Helianthus argophyllus and H. debilis spp. cucumerifolius and their hybrids from the african coast of the Indian Ocean and the USA using molecular markers. Helia. 27(40):123-132. Interpretive Summary: Sunflower is a plant of the North American continent, but now many wild species have spread to different parts of the world and become naturalized in the native floras. Two wild sunflower species, Helianthus argophyllus (silver leaf sunflower) and Helianthus debilis (cucumber-leaf sunflower) are found growing along the southeastern coast of Africa. We hypothesise that seeds of the two species were accidentally introduced in Africa by man from the area of origin of the two species, the coastal area of Texas. To investigate the origin of the populations, we compared African populations with a set of American populations of the two species from Texas using 20 nuclear microsattlite (SSR) markers and ten universal chloroplast SSRs. Six chloroplast SSRs and 13 nuclear SSRs were found to be useful, with six nuclear and four chloroplast markers showing polymorphism. The populations of the two species from the two continents appear to share the same alleles indicating a very recent divergence and/or a sustained gene flow. Whatever the way of colonization of the wild sunflowers in Africa, they appear to a sub-populations of the native North American species. This would suggest that the American populations served as the origin of the African populations, but to further confirm this, additional analysis using other markers will need to be done.
Technical Abstract: A comparison of Helianthus argophyllus and Helianthus debilis subspecies, cucumerifolius populations from the coast of Mozambique and Eastern South Africa and Texas, USA was carried out at Udine University (Italy). American populations were supplied by the USDA Northern Crop Science Lab, Fargo, ND (USA) while the populations from Africa were collected over several years by Udine researchers. Population comparisons were based on morphological traits and nuclear and chloroplast SSR markers of plants grown in pots in a growth chamber. All populations are of potential interest to breeding programs, as well as, for evolutionary studies. Hybrid populations involved both species and for some African swarms possibly H. annuus. For H. argophyllus, there is evidence of a bottleneck effect. Material coming from Texas showed a lower number of alleles in nuclear SSRs compared to the African material.