The herbicide imazamox may provoke temporary yellowing and growth retardation in IMI-R sunflower hybrids, more often under stressful environmental conditions. Although, photosynthetic processes are not the primary sites of imazamox action, they might be influenced; therefore, more information about the photosynthetic performance of the herbicide-treated plants could be valuable for a further improvement of the Clearfield technology. Plant biostimulants have been shown to ameliorate damages caused by different stress factors on plants, but very limited information exists about their effects on herbicide-stressed plants. In order to characterize photosynthetic performance of imazamox-treated sunflower IMI-R plants, we carried out experiments including both single and combined treatments by imazamox and a plant biostimulants containing amino acid extract. We found that imazamox application in a rate of 132 μg per plant (equivalent of 40 g active ingredient ha−1) induced negative effects on both light-light dependent photosynthetic redox reactions and leaf gas exchange processes, which was much less pronounced after the combined application of imazamox and amino acid extract.

The resistance of crops to herbicides can be due to target site based resistance or non-target site based resistance mechanisms or a combination of both. In non-target site resistance, the detoxification efficiency plays a major role by involvement of enzymes such as P450s, GTs, GSTs and ABC transporters. The resistance of the first commercial Clearfield sunflower hybrids (Imisun trait) to herbicides of imidazolinone group is based on a combination of both types of resistance. The target site resistance consists of a mutation in Ahasl1 gene, encoding the synthesis of the AHAS enzyme. The non-target site resistance is supposed to be due to intensified herbicide disposal and is not fully understood. The objective of this study was to detect the fast response of the glutathione-mediated detoxification system in IMI-R and IMI-S sunflower hybrids to the herbicide imazamox and to study the possible participation of GSTs in the enhancement of the hybrids' tolerance. The obtained results allow to presume that GSTs are involved in imazamox detoxification in the sunflower Imisun trait and thus contributing to its non-target site resistance.

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