Enhancing Growth and Productivity of ‘Anna’ Apple Orchards: Mitigating Abiotic Stresses Through Moringa Leaf Extract and Mannitol Foliar Application at Critical Stages

For improving the resistance of apple trees to abiotic stresses resulting from global climate changes and enhancing their growth, productivity and fruit quality, 'Anna' apple trees were foliar sprayed with Moringa leaf extract (MLE) at concentrations of 0 (control), 2, 4 and 6%, and mannitol (a sugar alcohol) at concentrations of 0 (control), 10, 20 and 30% alone, or in combination during critical phases, the full bloom stage, the fruit setting stage and a month later, in two consecutive seasons in 2020 and 2021. Under hot and dry summer conditions during the two studied seasons, all treatments led to significant increases in vegetative growth, chlorophyll content, macro- and micro-mineral content, fruit set, yield per tree, fruit weight, firmness, soluble solids content (SSC), and total sugars compared to the control. The highest branch length, number of leaves, and leaf area were recorded with the combined treatment of MLE at 4% and mannitol at 30%. While the highest total chlorophyll content was obtained by the combined treatment of 4% MLE and 20% mannitol. The combined treatment of 6% MLE and 30% mannitol recorded the highest leaf content of N, P, K and Fe, while the highest leaf content of Mn was recorded by the combined treatment of 4% MLE and 30% mannitol. The highest content of Zn was recorded by the combined treatment of 2% MLE and 30% mannitol. The highest percentage of fruit set (40.5%) and yield per tree (26.75 kg) were recorded by the combined treatment of 6% MLE and 30% mannitol compared to untreated control, which produced the lowest value for fruit set (21.83%) and yield (13.75 kg/tree). In the same trend, the combined treatment of 6% MLE with 30% mannitol achieved the highest fruit weight, firmness, SSC, total sugars, and lowest acidity, while in contrast it was in untreated control.