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.

Drought stress is one of the main constraints limiting worldwide crop production. Arbuscular mycorrhizae (AM) and plant growth-promoting bacteria (PGPB) such as Azotobacter chroococcum and Azospirillium lipofrum have been shown to alleviate drought stress effects. Therefore, the interaction effect of AM fungi [ Glomus mosseae , G. etunicatum , and a mix of these (G. mix), and PGPB bacteria ( Azotobacter chroococcum + Azospirillium lipofrum )] was investigated in 1-year-old walnut seedlings (cv. Chandler) under normal and drought stress conditions. Drought stress reduced growth (plant height, root length, number of leaves, and fresh weight) and leaf nutrient content (N, P, and Zn) significantly of walnut plants. In contrast, proline, total soluble sugar, starch peroxidase enzyme activity, and total phenolic content of walnut leaves increased under this stress. Application of fungi or bacteria, and especially their simultaneous use, alleviated the negative effects of drought stress on walnut seedlings. AM fungi and PGPB increased significantly the content of some metabolites, including total phenolic content, proline level, peroxidase activity, total soluble sugar, and starch content as well as peroxidase enzyme activity. This led to an increase in walnut plant growth under the drought stress condition. Among AM fungi, G. etunicatum was more effective in reducing drought stress symptoms than either G. mosseae or the G. mix of fungi. In conclusion, use of G. etunicatum , along with PGPB, can reduce negative effects of drought stress on walnut seedlings.

The main aim of the present investigation is modeling and optimization of a new culture medium for in vitro rooting of G×N15 rootstock using an artificial neural network-genetic algorithm (ANN-GA). Six experiments for assessing different media culture, various concentrations of Indole – 3- butyric acid, different concentrations of Thiamine and Fe-EDDHA were designed. The effects of five ionic macronutrients (NH₄⁺, NO₃⁻, Ca²⁺, K⁺ and Cl⁻) on five growth parameters [root number (RN), root length (RL), root percentage (R%), fresh (FW) and dry weight (DW)] were evaluated using the ANN-GA method. The R² correlation values of 0.88, 0.88, 0.98, 0.94 and 0.87 between observed and predicted values were acquired for all five growth parameters, respectively. The ANN-GA results indicated that among the input variables, K⁺ (7.6) and NH4⁺ (4.4), K⁺ (7.7) and Ca²⁺ (2.8), K⁺ (36.7) and NH₄⁺ (4.3), K⁺ (14.7) and NH₄⁺ (4.4) and K⁺ (7.6) and NH₄⁺ (4.3) had the highest values of variable sensitivity ratio (VSR) in the data set, for RN, RL, R%, FW and DW, respectively. ANN-GA optimized LS medium for G×N15 rooting contained optimized amounts of 1 mg L⁻¹ IBA, 100, 150, or 200 mg L⁻¹ Fe-EDDHA and 1.6 mg L⁻¹ Thiamine. The efficiency of the optimized culture media was compared to other standard media for Prunus rooting and the results indicated that the optimized medium is more efficient than the others.

Due to short shelf-life of ber fruits, developing postharvest protocols incorporating nonchemical compounds with the aim of extending its shelf life and maintaining quality is one of the major issues regarding ber fruit industry. The quality of ber fruits is greatly affected by postharvest factors especially temperature and fruit treatment. In the present study, the effect of chitosan coating and storage temperature on the physicochemical characteristics of ber fruits was investigated as a factorial experiment based on randomized complete block design with three factors (chitosan coating, storage temperature, and storage time). The ber fruits were soaked in 0%, 0.5%, and 1% chitosan solution and stored at 5 and 25°C for 28 days. Changes in fruit weight loss, shriveling, fruit firmness, total soluble solid (TSS), titratable acidity (TA), ascorbic acid as well as decay rate were periodically recorded. The results indicated that the chitosan coating significantly prevented from reducing of fruit weight, firmness, TSS, TA, and ascorbic acid content. Also, the chitosan coating controlled fruit decay. Chitosan at low temperature (5°C) had a greater positive effect on fruit shelf life and weight maintenance than 25°C. In the other words, storage temperature had influence on fruit quality and shelf life, so that the best temperature for storing of ber fruit was 5°C and fruits stored at 25°C were destroyed after two weeks. In general, the results showed that chitosan coating (1%) with low-temperature storage (5°C) is the most effective strategy for improving the physiological quality and prolong the shelf life of ber fruits.

Background: Flower development and sufficient fruit set are important parameters with respect to walnut yield. Knowledge about flowering genes of fruit trees can help to conduct better molecular breeding programs. Therefore, this study was carried out to investigate the expression pattern of some flowering genes (FT,SOC1,CAL,LFYandTFL1) in Persian walnut (cv. Chandler) during the growing season and winter dormancy.Results: The results showed that walnut flower induction and initiation in Shahmirzad, Iran occurred in early June and late September, respectively. After meeting chilling and heat requirement, flower differentiation and anthesis occurred in late-March and mid-April to early-May, respectively. Study of flowering gene expression showed that the expression of theFTgene increased in three stages including before breaking of bud dormancy, from late March to late April (coincided with flower differentiation and anthesis) and from late May to mid-June (coincided with flower induction). LikeFT, the expression ofSOC1gene increased during flower induction and initiation (mid-May to early-August) as well as flower anthesis (mid-April to early-May).LFYandCALgenes as floral meristem identity genes are activated byFTandSOC1genes. In contrast with flowering stimulus genes,TFL1showed overexpression during winter dormancy which prevented flowering.Conclusion: The expression ofFTgene activated downstream floral meristem identity genes includingSOC1,CALandLFYwhich consequently led to release bud dormancy as well as flower anthesis and induction. Also,TFL1as a flowering inhibitor gene in walnut showed overexpression during the bud dormancy. Chilling accumulation reducedTFL1gene expression and increased the expression of flowering genes which ultimately led to overcome dormancy.