**Acknowledgements**

to wild sunflowers may be common [124]. Also, it has been known that there are inter- and intraspecific hybridization between *H. annuus* and its close relatives including its related species [41, 64, 74, 125] or its volunteer plants [65, 69]. In case of gene flow between cultivated sunflower and *Helianthus petiolaris*, the proportion of crop-weed hybrids in the F1 generation varies between 0.3 and 0.5%, depending on flowering period and the presence of common pollinators [68], while in case of gene flow between cultivated and wild sunflower, it was reached

Gene flow from sunflower crops onto their wild relatives mediated by pollen is dependent on different factors. The overlap of flowering periods of cultivated sunflower and its wild relatives, the pollinators which they share, self-incompatibility of the wild species, diploidy, and high levels of cross-fertilization are all factors which contribute to the spontaneous hybridization [66]. However, the hybridization between the sunflower and its relatives can be absent due to the mismatch of the flowering periods, incompatibility, physical distance, differences in the genetic structure between the species and interspecific competition of pollen [89, 125]. Many studies [42, 70, 121] confirmed that the pollen transfer from the resistant crops to their relatives primarily depends on their distance to the pollen source and the plot size. Consequently, some authors [64] have confirmed, when studying gene flow from sunflower imidazolinones-resistant hybrids to their wild relatives, that the HR gene was transported to a distance greater than 30 m from the pollen source, while the percentage of the surviving offspring of wild relatives was reduced with the increase in the distance from the HR hybrid. Also, it has been confirmed that the gene flow from the crop sunflower to its wild form is reduced with an increase in their mutual distance, with it being 27% at a 3 m distance. However, gene flow has also been confirmed at a distance of over 1000 m from the pollen sources [89]. Additionally, it was determined that 42% of the wild offspring sunflower at a 3 m distance from the crop sunflower represented its hybrids, while at a distance of 200 m, this percentage was 10%, and 4% at a distance of 400 m [43]. Several authors [42, 45, 64] indicate that the wind direction affects the gene flow, which is ascribed to its influence on the flight

The main consequence of gene flow between crop and their wild relatives is the increasing of wild relative fitness as a consequence of introgressed genes, which can lead to the development of invasive weeds. Some studies confirmed fitness increase of hybrids between sunflower crop and their relatives [47], while the other [77] confirmed hybrids in the first generation after crossing had lower fitness than wild parent in natural habitats, but in the following generations, fitness of hybrid was recovered. Also, hybrids between crop and wild populations of sunflower express lower fertility than their wild counterparts [75]. Although, crop hybridization can reduce dormancy in a wild species, hybridization IMI-resistant hybrid and wild sunflower in Argentina did not alter seed dormancy [41], while F1 germination was

Strategies for prevention or reduction of gene flow between crop sunflower and its relatives can be developed based on understanding seed and pollen dispersal and influence of different factors on that processes. The biological barriers based on cytoplasmic male sterility, which disable of plants to produce viable pollen, could be good option to reduce gene flow

as high as 33% [69].

52 Herbicide Resistance in Weeds and Crops

of bees.

in sunflower.

greater in wild sunflower populations [126].

This work was supported by Ministry of Educattion, Science and Technological Development of Serbia.
