Zymoseptoria tritici development induces local senescence in wheat leaves, without affecting their monocarpic senescence under two contrasted nitrogen nutrition

•Regardless of nitrogen availability, septoria did not modify leaf apical senescence.•Pycnidia density decreased over time at low nitrogen availability.•Relative loss in green area was unaffected by nitrogen availability.•The relative yield loss by septoria would be unaffected by nitrogen.•Nitrogen residual in healthy part of infected leaves was that of control.

Zymoseptoria tritici causes large losses in wheat yield usually related to the losses of green area. However, the issue of whether green area losses result from the local necrosis or from acceleration in the monocarpic apical senescence remains open.The present study examined whether leaf inoculation with Zymoseptoria tritici modifies apical senescence of flag leaf in wheat cultivar Soissons grown under two contrasted nitrogen nutritions.The dynamics of local and apical senescences and the pycnidia number were measured repeatedly throughout the grain filling. Local and apical senescence were adjusted to functions, the parameters of which were analyzed according to nitrogen and inoculation treatments. The intra-leaf gradient of residual nitrogen concentration was measured at plant maturity.The relative rate of apical senescence increased twofold when fertilization was withheld. Both treatments, inoculation and nitrogen, generated a large range of disease that developed to different extents, resulting from different rates and timing. Local necrosis and pycnidia number strongly varied with nitrogen nutrition but necrosis varied in the same extent as apical senescence, thus green area relative loss was unaffected by nitrogen nutrition. By opposition, apical senescence was never affected at any time by the inoculation. Residual nitrogen increased in the inoculated portions of the infected leaves, in correlation with local necrosis, whereas the residual nitrogen in the non-inoculated part of infected leaves stayed at the level of control leaves.Apical senescence was managed at the leaf tissue level, according to nitrogen availability but regardless of disease, a useful output for modelling.

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