Abstract
Wild sunflower (Helianthus annuus L.) is an invasive species widely distributed in several regions of the world, where it shares a large area with domesticated sunflower. The imidazolinone-tolerant sunflower enables the control of problematic weeds (such as Xanthium spp., Brassica spp., wild sunflower) with imidazolinone herbicides (Clearfield® production system) in cultivated sunflower crops, but could facilitate the gene transfer of herbicide resistance, from cultivated sunflower to wild sunflower, generating hard-to-control weed biotypes or herbicide-resistant populations. The development of new practices that involve the selective inhibition of reproduction structures, such as pollen granules, could be an innovative strategy to minimize outcrossing and the origin of weed–crop hybrids in Clearfield® production systems. In this study, the effects of mugwort (Artemisia vulgaris L.) aqueous extract on cytosolic Ca2+ and the germination of pollen grains collected from conventional, wild and IMI-tolerant sunflower were tested. The results showed that mugwort deregulated Ca2+ homeostasis and markedly reduced the germination of conventional and wild sunflower pollen, but not IMI-tolerant pollen. The HPLC analysis revealed the presence of phenolic acids belonging to the hydroxycinnamic and benzoic classes in the mugwort extract. Hydroxycinnamic acids (caffeic and ferulic) deregulated the cytosolic Ca2+ of conventional and wild sunflower pollen, but not those which were IMI-tolerant, similar to mugwort extract. Selective inhibition of wild sunflower pollen in the Clearfield® sunflower crop contributes to a possible new weed management strategy, reducing the wild sunflower reproduction by seed, minimizing the potential risks of outcrossing with the formation of weed–crop hybrids. The Ca2+ selective chelating activity of caffeic or ferulic acids provides elements to be investigated for their possible use as an alternative to mugwort extract.
Highlights
IntroductionIn conventional sunflower varieties, is very difficult and mainly based on non-chemical strategies, such as false seedbed technique and mechanical methods, because pre- and post-emergence herbicides are not effective [4,5]
Wild sunflower (Helianthus annuus L.) is an invasive species widely distributed in several regions of the world, including several main sunflower-producing countries, such as Argentina, France, Italy, Serbia and Spain, where it shares a large area with domesticated sunflower [1]
Imidazolinone herbicides control weeds by inhibiting the enzyme acetohydroxyacid synthase (AHAS), called acetolactate synthase (ALS), which is a critical enzyme for the biosynthesis of branched chain amino acids in plants
Summary
In conventional sunflower varieties, is very difficult and mainly based on non-chemical strategies, such as false seedbed technique and mechanical methods, because pre- and post-emergence herbicides are not effective [4,5] Both pre-emergence herbicides applied when sowing sunflower crops to prevent the germination of weed seeds and post-emergence herbicides applied after sunflower emergence to kill weeds after they have germinated are not selective on cultivated sunflowers, and at the same time, are effective against wild sunflower. Given the existence of wild H. annuus populations established in several regions of the world, and the possibility of breeding fertile hybrids with cultivated sunflowers, the widespread usage of IMI technology could favor the gene transfer of herbicide resistance from crops to wild species, generating noxious weed biotypes difficult to control [6]. If weeds gain the herbicide-tolerance trait from the crops, the herbicide will fail to control the weeds effectively and may result in herbicide-resistant populations
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