Soluble sugars, phenolic acids and antioxidant capacity of grape berries as affected by iron and nitrogen

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anglais. Foliar nutrition is one of the effective cultural practices in vineyards. In this research, the effect of iron chelate (Fe-EDDHA) and urea, each in three levels of 0, 0.5 and 1%, was evaluated with an ANOVA completely randomized block in commercial vineyard (cv “Sultana”) located in Bahareh village of Malayer city (Iran). Vines were sprayed in three stages: a week before bloom (8 June), 2 weeks after bloom (29 June) and 5 weeks after bloom (20 July) during the growth seasons in 2015 and 2016. The grapes harvesting was done in mid-September according to the maturity level of untreated vines. In comparison with the other treatments, moderate levels (0.5%) of fertilizers allow to reach the highest glucose and sucrose concentration at harvest. Foliar spray of high iron chelate doses in combined with 0.5% urea caused a considerable increase in berries putrescine and spermine concentration. However, combination effects of urea and Fe-EDDHA with moderate level (0.5%) were the most efficient for spermidine accumulation of ‘Sultana’ grapevine. For the moderate levels (Fe-EDDHA 0.5%) of fertilizers treatment, most phenolic acids and anthocyanidins reached a peak, and the highest free radical scavenging capacities (DPPH) of grape samples were achieved. The activity superoxide dismutase, guaiacol peroxidase, catalase and ascorbate peroxidase increased with moderate levels of Fe-EDDHA in combination with high levels of urea treatments. However, the maximum glutathione reductase was obtained with 1% urea in combination with Fe-EDDHA at 1% concentrations. Altogether, data showed that iron and nitrogen are highly efficient to manage quality and nutritional potential of grape berries.