Two introduced wild species Helianthus annuus L. and H. petiolaris Nutt. have become widespread in central Argentina and overlap the sunflower crop region. Intermediate off-type plants between the wild and cultivated species are often found, which is of concern because of the recent release of imidazolinone resistant varieties and the likely use of genetically modified sunflower cultivars. The progeny of 33 off-type plants obtained from 14 representative sites of the diffusion area were studied to confirm hybrid origin. Germination, survival, morphological traits and days to flowering confirmed hybridization between crop and both wild species, when compared to eight accessions of typical wild plants. Some progenies were presumably crop-wild H. annuus hybrids, some originated from the cross of cultivated plants and H. petiolaris, and two were the advanced generation of a cultivated hybrid. Hence, morphological traits are a good clue for the identification of spontaneous hybrid plants at field. The results indicate that crop-wild hybridization and introgression occur at various places in central Argentina. This fact may represent a way to herbicide resistance escape and future transgene escape if GM sunflower cultivars are released for commercial use.

Disc flowers of Helianthus petiolaris (Asteraceae) are usually purple red due to anthocyanin pigments in corolla lobes, style and stigma. However, yellow-flowered plants are occasionally found. The inheritance of this trait was studied through crosses between different phenotypes and the results indicated that flower color is controlled by two genes with complementary action, both loci being dominant and independently inherited. This agrees with results obtained in cultivated sunflower, H. annuus, where one to three dominant genes have been proposed for anthocyanin expression in different organs.