Effect of Drought Stress on Water Relative Content of Leaf and Antioxidant Enzymes Activity in Some Hybrid Apple Rootstocks

In order to evaluate the drought tolerance of some hybrid apple rootstocks, a factorial experiment was conducted base on randomized complete block design with 11 rootstock genotypes obtained from the apple rootstock breeding program, including AR1 to AR11, with MM111 rootstock as control in two irrigation treatments (40) and 80 (control) percent of usable water in the soil was applied. The water relative content of leaf and enzymes superoxide dismutase, peroxidase, ascorbate peroxidase, catalase and hydrogen peroxide were measured in leaf samples. The results showed that the water relative content of leaf, the activity of superoxide dismutase, peroxidase and ascorbate peroxidase enzymes and hydrogen peroxide were significantly affected by the rootstock genotype and the interaction effect of stress level and rootstock genotype. Drought stress caused a decrease in the relative water content of leaves in all the genotypes, but AR4, AR8, and AR11 genotypes had less differences compared to control irrigation. Drought stress increased the activity of superoxide dismutase, ascorbate peroxidase and peroxidase and hydrogen peroxide in the leaves of rootstock genotypes. The comparison of the activity of enzymes under drought stress compared to control irrigation treatment showed the activity of antioxidant enzymes increased in genotypes AR3, AR4, AR7, AR8, AR11 and hydrogen peroxide accumulation in genotypes AR3, AR6, AR7, AR10. Therefore, the genotypes of AR4, AR8, and AR11 under drought stress conditions, with high relative leaf water content and higher antioxidant enzyme activity, are evaluated as tolerant to drought stress compared to other genotypes.