Introduction
Cross breeding processes including targeted crossings to increase drought tolerance, can be considered as a safe and permanent solution to reduce the harmful effects of drought stress on plants. Therefore, two issues of pistachio as a strategic crop in the country and location of Iran in arid and semi-arid region necessitated research in order to achieve rootstocks drought-tolerant hybrids are necessary.
 
Materials and methods
The experiment was conducted as factorial based on a Completely Randomized Design with four replications in the research greenhouse of Gorgan University of Agricultural Sciences and Natural Resources during 2018-2019. The treatments were consisted of 10 pistachio genotypes Ahmad Aghaei, Akbari, Sorkheh Hosseini, Garmeh, Fandoghi and interspecific hybrids (Ahmad Aghaei­×Integerrima, Akbari­×Integerrima, Sorkheh­ Hosseini­× Integerrima, Garmeh­×­Iintegerrima and Fandoghi­×­Integerrima) and three levels of drought including control (field capacity), mild stress (65% of field capacity) and Severe stress (30% of field capacity) were applied on 3 months old the seedlings for 84 days.
 
Results and Discussion
According to the results, fandoghi genotype showed a higher malondialdehyde concentration in leaves (280.23 %), while the hybrid genotypes of Sorkheh Hosseini­×­Integerrima, Ahmad Aghaei­×Integerrima and Akbari­× Integerrima showed a lower malondialdehyde concentration in leaves by 70.18, 76.70, 81.03 % respectively compared to the control. Several osmotic mechanisms are carried out by plants, especially pistachios, in stressful conditions to reduce the effects of drought stress. In fact, these mechanisms have enabled plants to withstand the damages caused by drought and have made plants able to recover their biochemical and physiological functions faster after removing the stress factor. For example, a general physiological mechanism adopted by plants to cope with abiotic stresses is the production of large amounts of low molecular weight, water-soluble, non-toxic organic compounds even in high amounts called osmolytes. One of the most important of them is proline. Therefore, the genotypes with higher amount of proline can be more tolerant to drought conditions. The next osmolyte is glycine betaine, which has a significant protective role in the stability of enzymes and the structure of plasma membranes when faced with drought stress. Therefore, glycine betaine plays a significant role in the resistance of plants to stress through the protection of enzymes, the photosynthetic apparatus, the elimination of free radicals, the preservation of membrane integrity, the protection of large molecules, and as a non-toxic compatible osmolyte. It has an environment. Carbohydrates also increase membrane stability in response to drought stress. Therefore, the accumulation of carbohydrates in the osmotic responses of plants is one of the factors that can prevent disorders in the cell membrane. In addition, phenols are also one of the antioxidant mechanisms of plants in drought stress conditions, because such compounds act as scavengers of reactive oxygen species and thus stabilize membrane, cells and prevent lipid peroxidation. Malondialdehyde is also a decomposition product of unsaturated fatty acids and hydroxides and is used as a suitable marker for lipid peroxide. Therefore, the amount of malondialdehyde obtained from the peroxidation of membrane lipids is used as an indicator for oxidative damage in most cases.
Conclusion
Based on the results of the present research, it seems that it is possible to use the hybrids of Sorkhe Hosseini × Integerrima, Ahmad Aghaei­ ×­ Integerrima, and Akbari­× ­Integerrima as drought-tolerant genotypes in dry areas. Therefore, based on the results of the present research, it seems that the plants in question can be used as drought tolerant genotypes in arid regions.