Evaluation of some Vegetative and Physiological Traits of Domestic Pistachio Seedlings in Controlled Crosses with Integerrima Pollen Grains in Order to Access Drought Tolerant Genotypes

Introduction: Agriculture of Iran is known worldwide for its pistachio (Pistacia vera L.) and is one of the most important non-oil exports. Therefore, attempts to improve the yield can be one of the primary goals in the pistachio industry in Iran. Due to the drought problem in Iran, increasing the cultivation area to increase production may not be a good option. Therefore, the purpose of this study was to compare the drought tolerance of different pistachio seedlings from open pollination and pollinated with domestic species pollen and controlled crosses using integerrima pollen in order to find the most tolerant genotypes.Materials and Methods:The first step: Controlled pollination and hybrid seed production In order to produce hybrid seeds, a controlled pollination using integerrima pollen grains at Razavi Pistachio Research Institute was conducted for five cultivars; Ahmad Aghaei, Akbari, Sorkheh Hosseini, Garmeh and Fandoghi. Each replication had a tree and from each tree, seven branches were selected that had at least three to four flower buds and four branches from it for controlled pollination, two branches for open pollination and a branch was considered for negative control. Before the flower clusters were fully opened, 70% alcohol was sprayed on the branches to prevent the possibility of unwanted pollen. In order to ensure controlled pollination, in the bud swelling stage, the branches were isolated by double-layered bags measuring 30 × 45 cm. Pollen was collected from the Arzooieh area of Kerman province to select the male parent of integerrima. Then, a combination of flour and integerrima pollen (1:1 ratio) was injected into the insulating bags and pollination was performed. In late summer, hybrid seeds were harvested.The second stage: Drought resistance test of hybrids obtained from first step The experiment was conducted as factorial based on a Completely Randomized Design with four replications at the research greenhouse located in Gorgan University of Agricultural Sciences and Natural Resources during 2019-2020. The treatments were consisted of ten pistachio genotypes; Ahmad Aghaei, Akbari, Sorkheh Hosseini, Garmeh, Fandoghi and (hybrids between integerrima as the pollinizer and genotypes of Ahmad Aghaie, Akbari, Sorkheh Hosseini, Garmeh and Fandoghi were applied as the maternal parent 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 seedlings for 84 days. Seeds obtained from free and controlled pollination were planted in pots with a diameter of 33 cm and a height of 35 cm on April 6, 2017. Three seeds were planted in each experimental unit, and after planting and ensuring establishment, the number of plants in the pot was reduced to the final level of one in each pot. Each replication was consisted of four experimental units or four pots, and each pot was contained a plant. At the end of the experiment, growth and physiological parameters were measured. Statistical analysis of the results was performed using SAS 9.1 software.Results and Discussion: Results of statistical analysis showed drought stress had a significant effect on leaf number, stem length, root length, leaf relative water content, electrolyte leakage, chlorophyll a, chlorophyll b, total chlorophyll, carotenoid, and leaf and root proline content. With increasing drought levels, all traits except root length, electrolyte leakage and proline content were reduced in comparison with control.  Sorkheh Hosseini × integerrima, Ahmad Aghaei × integerrima, Akbari × integerrima interactions and genotypes of fandoghi and fandoghi × integerrima interaction were superior in the most of traits by drought, respectively. Based on the results it seems hybrids of Sorkhe Hosseini × integerrima, Ahmad Aghaei × integerrima and Akbari× integerrima crosses will be used as genotypes with dry-tolerant genes to modify cultivars in arid regions.