The role of leaf senescence in relation to nitrogen uptake and translocation to the reproductive plant organs for genotypic differences in nitrogen efficiency of rapeseed

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Decreasing the high nitrogen (N) balance surpluses in winter oilseed-rape production requires the breeding and cultivation of N-efficient cultivars. The overall objective of the project is the clarification of the role of leaf senescence and N mobilization from leaves in grain yield formation of rapeseed genotypes at limited N supply (N efficiency). The project thus represents the bridge between the projects within the research groups dealing with molecular aspects of N dynamics during leaf senescence and the oilseed-rape breeders aiming at improving the N efficiency of the crop. We hypothesize that (i) genotypic differences in delayed leaf senescence are governed by root growth and activity and/or leaf-inherent factors which can be characterized already at early vegetative stages and (ii) the main effects of delayed leaf senescence on reproductive yield are higher photosynthetic productivity of the leaves and longer duration of N translocation to the reproductive organs. To test these hypotheses we will conduct experiments with genotypes differing in N efficiency and leaf senescence at yield/growth-limiting and unlimiting N supply in the field in cooperation with a rapeseed breeder, under controlled conditions until maturity, and at the seedling stage in cooperation with the molecular working groups.