6533b850fe1ef96bd12a8157

RESEARCH PRODUCT

Les ambroisies annuelles (Ambrosia artemisiifolia et Ambrosia trifida) : réponse adaptative au désherbage chimique et connectivité des populations dans les paysages agricoles

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The primary aim of this work was to study the risk of resistance evolution to acetolactate synthase (ALS) inhibiting herbicides in mugwort (Ambrosia artemisiifolia L.) through four points: (i) selection pressure (study of the efficacy of a range of ALS-inhibiting herbicides), (ii) the adaptive response capacity of the weed (determination of the variation in sensitivity to ALS inhibitors between plants and implementation of a recurrent selection programme), (iii) a field study (search for resistance to ALS inhibitors in the field in France), (iv) the study of resistance mechanisms (target-linked - TLR - and non-target-linked - NLR - by a transcriptomics approach). The second objective was to study the connectivity of A. artemisiifolia populations in agricultural landscapes using microsatellite markers developed during this work in order to determine the factors that could facilitate the dispersal of this species and of resistance at the agricultural landscape scale.With regard to herbicide resistance:The response of A. artemisiifolia to ALS inhibiting herbicides is highly variable between substances.Plants surviving the maximum permitted dose and higher doses of metsulfuron were selected to start a recurrent selection programme. After two cycles of selection, there was an intensification of metsulfuron resistance and an emergence of imazamox and tribenuron resistance.Three cases of imazamox resistance were identified in the field, including two cases of pure RNLC and one case of RLC - RNLC coexistence.A transcriptome of A. artemisiifolia was generated using the PacBio sequencing technique to search for genes involved in RNLC mechanisms (RNAseq approach). 62 candidate genes were identified, including ABC transporters, cytochromes P450 and glutathione-S-transferases known to be involved in herbicide degradation.For the study of population connectivity :26 microsatellite markers were developed and revealed high genetic variability. Genetic structuring was studied on a large scale for A. artemisiifolia populations in Europe (invasion area) and North America (area of origin). At a finer scale (agricultural landscape), the genetic structure of populations is still influenced by colonisation events. The migration events that have been identified between areas of ragweed presence suggest moderate gene flow (pollen/seed) and connectivity at the scale of an agricultural territory. In agricultural environments, dispersal of herbicide resistance alleles could easily occur from close to home via pollen flows, and also at longer distances via seed dispersal. Anthropogenic activities play a major role in seed dispersal (agricultural machinery, contaminated seed lots...).Analysis of the reproductive system confirmed that this species is allogamous, which leads to significant intra- and inter-population gene flow.The knowledge acquired in the course of this work could help to develop better adapted control strategies to efficiently fight against A. artemisiifolia in order to limit its expansion, such asDiversified weed control strategies: combination of mechanical (including false seeding) and chemical control (diversification of herbicide modes of action).Extending and diversifying crop rotations by favouring winter crops and/or covering and competitive crops. This knowledge could also be used to combat another weed of the Ambrosia genus, Ambrosia trifida.