Effect of grape pomace powder on nutrients content, phytochemicals and tolerance to bicarbonate-induced iron chlorosis in Thompson Seedless grapes

The present experiment was carried out as a factorial (4 × 2) based on a completely randomized design on grapevine cultivar ‘Thompson Seedless’ hydroponically in greenhouse conditions. The first factor was four levels of dried grape pomace (GP; 0, 2.5, 5 and 10 g/kg of culture medium) and the second factor included two bicarbonate concentrations (0 and 10 mmol/L sodium bicarbonate; SB). Based on the results, significant differences were observed between the used treatments. The highest levels of leaf proline and soluble sugar were observed in vines treated with 10 mmol SB and 5 g of GP. These treatments also increased total leaf flavonoid and phenol content in the vines. The highest greenness and nitrogen, potassium, phosphorus, iron, zinc, and manganese content were observed in the leaves of vines treated with 10 g of GP without SB application. Also, the highest ion leakage and malondialdehyde content were recorded in vines treated with 10 mmol of SB and without GP. Also, adding 10 mmol SB increased hydrogen peroxide (H2O2) content, while using 2.5, 5, and 10 g of GP decreased this indicator. The highest catalase enzyme activity was observed in vines treated with 10 mmol SB and 10 g of GP. In addition, increasing the SB concentration from zero to 10 mmol increased guaiacol peroxidase and ascorbate peroxidase enzymes activities in all treatments. In general, GP powder, by affecting acidity and water relations in the rhizosphere while reducing chlorosis, increased plant tolerance to SB- induced stress.