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Ethephon‐induced leaf senescence increases the concentration of yeast‐assimilable nitrogen in grape must (
 
 Vitis vinifera
 
 cv. Riesling)

Background and Aims: Leaf senescence induces a massive shift of the nitrogen (N) allocation within plants, but its influence on the storage of yeast-assimilable N (YAN) in grapevine berries is unclear. The aim of this work was to investigate whether the YAN concentration in grape must can be increased by a targeted induction of leaf senescence. Methods and Results: Leaf senescence was induced in two consecutive seasons by an ethephon treatment of grapevines (Vitis vinifera cv. Riesling) before harvest, and its effect on the amino acid and ammonium balance of berries and must, as well as on alcoholic fermentation performance was investigated. The ethephon-induced senescence caused a significant increase in YAN concentration in berries and must, based on a general increase in most amino acids. Compared to natural senescence, the ethephon treatment led to a lower proline : arginine ratio, a lower sugar concentration in the must and a lower grape yield. Conclusions: Ethephon-induced leaf senescence enhances the nutritional value of grapes and improves the fermentability of grape must. Significance of the Study: Our results enable wine producers to improve the nitrogen use efficiency of vines and to ensure a balanced N nutrition of the yeast.