Fifty-eight mature Persian walnut (Juglans regia) seedlings growing at six sites in the mountainous regions of Taft, in central Iran, were evaluated to determine their morphological variation and to identify promising individuals. The traits investigated included phenological characteristics, such as budbreak and nut maturity time, and nut characteristics, such as nut and kernel weight, kernel ratio, and shell thickness. Yield efficiency and fruitbearing habit were also investigated. The average fruit characteristics: nut weight, kernel weight, kernel ratio, and shell thickness were in the range of 6.0-15.2 g, 2.6-9.1 g, 38.4-79.6%, and 0.4-1.4 mm, respectively. The promising genotypes were AA 33 thickness (0.67), kernel weight (0.75), and shell thickness (0.32); whereas a negative correlation was detected between shell thickness and kernel ratio (-0.34). The data correlation matrix was subjected to principal component analysis, a technique that reduced the dimensionality of the data set and revealed the dominating variables. Cluster analysis of the selected genotypes detected three cluster groups. However, no significant relationship was found between morphological diversity and site geography. The promising selected genotypes identified in central Iran will be further exploited by walnut breeding programmes for their tree and nut characteristics.

The production and consumption of nuts are increasing in the world due to strong economic returns and the nutritional value of their products. With the increasing role and importance given to nuts (i.e., walnuts, hazelnut, pistachio, pecan, almond) in a balanced and healthy diet and their benefits to human health, breeding of the nuts species has also been stepped up. Most recent fruit breeding programs have focused on scion genetic improvement. However, the use of locally adapted grafted rootstocks also enhanced the productivity and quality of tree fruit crops. Grafting is an ancient horticultural practice used in nut crops to manipulate scion phenotype and productivity and overcome biotic and abiotic stresses. There are complex rootstock breeding objectives and physiological and molecular aspects of rootstock–scion interactions in nut crops. In this review, we provide an overview of these, considering the mechanisms involved in nutrient and water uptake, regulation of phytohormones, and rootstock influences on the scion molecular processes, including long-distance gene silencing and trans-grafting. Understanding the mechanisms resulting from rootstock × scion × environmental interactions will contribute to developing new rootstocks with resilience in the face of climate change, but also of the multitude of diseases and pests.

Selecting salt tolerant rootstocks is a sustainable approach for developing fruit trees in salinity prone areas. 60-day-old seedlings of <em>Pistacia vera </em>‘Akbari’ and ‘Ghazvini’, and <em>P. vera</em> ‘Ghazvini’ × <em>P. atlantica </em>(G×A) were subjected to 0, 50, 100 and 150 mM NaCl in half strength Hoagland’s nutrient solution. After 45 days, the growth, water relations, and oxidative damage parameters were investigated. Salt stress reduced plant biomass, height, crown diameter and leaf number, but increased specific leaf area (SLA) of the seedlings. Under salt stress, the growth of ‘Akbari’ seedlings was higher than the other genotypes. Accumulation of malondialdehyde (MDA) and proline was observed in the leaves of salt affected seedlings. ‘Ghazvini’ seedlings had the highest MDA concentration and the lowest cell membrane stability in their leaves. Degredation of photosynthetic pigments under salt stress was lower in the leaves of ‘Akbari’ seedlings than that in other genotypes. Increase in leaf succulence was observed in ‘Akbari’ and G×A seedlings in response to salt stress. Relative water content and concentration of anthocyanins in the leaves of pistachio genotypes remained unchanged under salt stress. The results revealed that monitoring leaf abscission, SLA, leaf succulence, MDA concentration, and photosynthetic pigments provide suitable contrast for screening salt tolerance in pistachio. Furthuremore, ‘Akbari’ was found to be the most salt tolerant genotype.

Physio-biochemical responses of pistachio varieties including Pistacia vera L. ‘Ghazvini’ (GH), P. vera ‘Ghermez-Pesteh’ (GP) and P. atlantica subsp. mutica (M) were assessed under salt stress to understand the common mechanisms of salt tolerance in two popular Pistacia species. In the experiment, half-sib seedlings of the varieties were subjected to high (100 mM) and severe (200 mM) levels of NaCl-induced salinity for 90 days. Growth, physiological, biochemical and ionic parameters in the roots and shoots of plants were measured in the experiment. Salinity markedly declined plant growth, and increased the number of necrotic leaves (NL) and leaf abscission. In terms of physiological responses, salinity reduced the relative water content (RWC), membrane stability index (MSI) and the concentrations of photosynthetic pigments, but increased carbohydrates and proline content in the leaves. MSI of the leaves was positively correlated with the concentrations of anthocyanins and carotenoids. Salinity increased sodium content in root and shoot tissues of the plants, and decreased potassium concentration and K/Na ratio. Among the rootstocks, GH had better performance on all parameters. Despite the high concentration of Na+ and low K/Na ratio in the shoots, the lowest number of NL was found in GH under both salinity levels. The results indicated that salt tolerance in GH was most likely related to compartmentation of Na+ ions. Finally, accumulation of osmolytes and sodium compartmentation were considered to be the most important mechanisms in the salt tolerance of pistachio rootstocks.

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