Assessment of Mating System in Helianthus annuus and H. petiolaris (Asteraceae) Populations

subsp. and are wild North American species that have been naturalized in central Argentina. They have a sporophytic self-incompatibility genetic system that prevent self-fertilization but the occurrence of self-compatible plants in Argentina was observed in both species and could in part explain their highly invasive ability. Their geographical distribution coincides with the major crop area. The domestic sunflower is self-compatible, can hybridize with both species and presents a considerable amount of gene flow. The aim of this study is to understand the self-incompatibility mechanism in both wild species. Reciprocal crossing and seed production were used to identify self-compatible genotypes, the number and distribution of self-incompatibility alleles within populations and the type and extent of allelic interactions in the pollen and pistil. The behaviour of S alleles within each population was explained by five functional S alleles and one non-functional allele in each species, differing in their presence and frequency within accessions. In both species, the allelic interactions were of dominance/recessiveness and codominance in pollen, whereas it was only codominance in the pistil. Inbreeding effects in wild materials appeared in the third generation of self-pollination, with lethal effects in most plants. The number of S alleles is low and they behave in a similar way of other Asteraceae species. The self-compatibility was addressed to non-functional S alleles introgressed in wild plants through gene flow from self-compatible sunflower.