Effet d'un rapport de Sillicium sur la senescence foliaire et les performances agronomiques du colza

Abstract : Rapeseed (Brassica napus L.) is a crop that requires high nitrogen inputs and has a low Nitrogen Utilization Efficiency (NUE) mainly due to a low remobilization efficiency during leaf senescence. Currently, an improvement of the agro-environmental balance of rapeseed, requires the development of new cultural practices to maintain (or even improve) its yield in response to low nitrogen inputs. In this context, the use of beneficial element such as silicon (Si) with previously demonstrated effects on tolerance to some nutritional stress (phosphorus and potassium), constitutes an interesting alternative. The objectives of this study are to investigate the effect of Si on the progression of leaf senescence, nitrogen uptake and remobilization but also on agronomic performances of rapeseed grown in hydroponics or in field conditions and submitted or not to a limitation or deprivation of nitrogen inputs. Our work shows that despite being considered as a low Si accumulator, rapeseed takes up and stores Si mainly in its roots. In addition, a Si supply for a short time (7 days; 1.7 mM) to young plants deprived of nitrogen leads to a delay of senescence of mature leaves associated with a maintenance of their chlorophyll content and their photosynthetic activity. In addition, in field conditions, a supply of Si (12 kg ha-1) to plants grown with 160 kg N ha-1 leads to an increase of yield (+4.2 quintals ha-1). Furthermore, calculation of the "Agronomic Nitrogen Recovery (ANR)" combined with the expression of genes encoding nitrogen transporters (BnaNRT1.1, BnaNRT2.1, and BnaAMT1.1) shows that Si increases the nitrogen uptake. Finally, a differential analysis by RNAseq of roots transcriptomes from young plants treated or not with Si for a short time (7 days; 1.7 mM), shows that Si modulates the expression of 1079 genes, 334 being induced and 745 repressed. This result indicates that in addition to its mechanical role, Si acts also a signal, a role very poorly demonstrated in the literature.
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Cylia Haddad. Effet d'un rapport de Sillicium sur la senescence foliaire et les performances agronomiques du colza. Sciences agricoles. Normandie Université, 2018. Français. ⟨NNT : 2018NORMC270⟩. ⟨tel-02159553⟩

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