effects of drought stress on some morphological, physiological and biochemical parameters of persian walnut seedling (juglans regia l.)

iran is among the world's arid and semi-arid countries. drought stress is one of the most important environmental stresses affecting fruit trees and considerably can cause yield reduction. persian walnut (juglans regia l.) with significant area harvest is one the most important nuts in iran which require sufficient amounts of water for optimal growth and efficiency. in order to study the effect of different levels of water stress on some morphological and physiological parameters of persian walnut and to determinate the tolerance of the seedlings to drought stress, the experiment has been carried out as factorial based on completely randomized design in a controlled greenhouse with nine treatments and 20 replications. in this study, stress levels including control (80% of field capacity), moderate drought stress (50% field capacity) and severe drought stress (20% field capacity) were applied and measurements were carried out through three stages. the results of morphological, physiological and biochemical parameters showed that these parameters have been affected by the stress levels. it was found that the walnut seedlings could not able to tolerate the moderate drought stress even at 50% of field capacity. therefore, the intolerance of walnut seedlings to moderate and severe levels of drought stress was accounted to the increased ion leakage, reduced leaf relative water content, chlorophyll degradation, decreasing the amount of reduced sugars, proteins and increase in proline and hydrogen peroxide as well as an inefficient antioxidant enzymes for stress tolerance.