CONICET | Buscador de Institutos y Recursos Humanos

Wild species exploration and collection Two wild annual sunflower species, Helianthus annuus and H. petiolaris, were introduced in Argentina about 50 years ago and became naturalized. At present, they are widespread over seven provinces of the central part of the country, between 31.3º and 38.7º S latitude, 60.6º and 68.3º W longitude. H. annuus grows in different habitats and soils, from eastern Entre Ríos to western Mendoza and San Juan provinces, being in Córdoba the largest populations. H. petiolaris is more restricted to sandy soils of central La Pampa and their bordering Buenos Aires and San Luis provinces. Gene flow between both species and the cultivated sunflower is evidenced by intermediate forms seldom found in wild populations and tilled lands. At present, our collection has 135 H. petiolaris, 90 H. annuus accessions and samples from over 20 localities where hybrid forms are common. Besides, there are wild entries from the centre of origin in North America at germplasm banks, comprising annual and perennial species, at two experimental stations of the National Institute of Agricultural Research, INTA. Phenotypic diversity Both naturalized species display phenotypic diversity, though not representing the extreme variability found in North America. Highly significant differences among populations were found for a number of morphological traits in both species. Principal component analysis did not show definite clusters, or correlation with geographical distribution for H. petiolaris, but the amount of variation was higher in regions of traditionally sunflower crop production. Plant cycle was correlated with geographic position and bract (phyllary) width, a trait influenced by gene flow from the crop. A founder effect was not evident and we did not find hints about the species spreading over the country. Multivariate analysis in H. annuus did reveal population clusters that allow infer about dispersion processes. Successive explorations indicate that both species continue to spread. Naturalized wild H. annuus populations display some promising traits for breeding. Variation in oil fatty acid composition, life cycle (phenology), resistance to diseases, presence of male sterility and tolerance to imazapyr are currently investigated. H. petiolaris also shows resistance to fungus diseases and tolerance to the parasitic plant Cuscuta indecora var. longisepala. Molecular diversity Isozymes and SSR analysis revealed high genetic variability in local populations of wild H. annuus. The presence of different unique alleles over the whole range of distribution points to multiple introduction events. Allelic composition of wild and crop was similar and we were not able to find specific markers for the crop. It should also be considered that the local populations might have been under crop genetic flow in the native range, before their introduction. Genetic differentiation among H. petiolaris populations based on RAPD data showed a highly significant variation among populations, but also within them (Fst=0,395). Hybridization and gene flow Presumable F1 hybrid plants were detected in the wild because of intermediate morphology, and analysis of their families in a common garden confirmed the hybrid status. However, backcrosses or advanced hybrid generations are not easily recognized based on morphological traits. Gene flow from the crop to both wild species was estimated in progenies of sampled heads, either by morphological traits or molecular markers. Gene flow from the wild species to the crop was also confirmed. RAPD markers allowed identification of crop bands in H. petiolaris hybrids, which showed a combination of parental bands, although a petiolaris-like molecular phenotype was also frequent among hybrids. Unique bands in cultivated sunflower constitute potential useful markers to estimate gene flow.

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