Grafting commercial cultivars of almonds on accurate rootstocks mitigates adverse effects of drought stress

Abstract Tolerance to drought can be improved by grafting commercial varieties onto drought tolerant rootstocks. The interaction of rootstock and scion might be a mechanism for resistance to the environmental stresses such as drought in almonds. The aim of this research was to study if short-term exposure to drought in grafted plants using diferent rootstocks would show tolerance to drought now. To fulfill this objective, some parameters (proline content, soluble carbohydrates, malondialdehyde (MDA), electrolyte leakage (EL) and antioxidant enzymes activity such as ascorbate peroxidase (ASC) and peroxidase (POD), relative water content (RWC), stem water potential (ΨSWP or SWP) and water use efficiency (WUE)) of scions (5 commercial almonds) grafted on 3 rootstocks were analyzed. Factorial study based on randomized complete block design with three replications was carried out to determine the most tolerance compound. The factors included cultivars in 5 levels (‘Supernova’, ‘Texas’, ‘Marcona’ ‘Shokoufeh’ and ‘K13–40′), rootstocks in 3 levels [(peach × almond hybrids: ‘GF677’, ‘GN22’ and ‘seedling bitter almond ‘No.32′] and drought stress in 4 levels (No: -0.1 MPa (NS), Moderate: -0.7 MPa (MS), Severe: -1.1 MPa (SS) and very severe: ΨSWP ≤ -2.8 MPa (VSS). The results revealed that increasing drought stress leads to a decrease in the proline content, soluble carbohydrates, MDA, EL, and the activity of ASC and POD enzymes in various rootstock-scion grafted were increased. In the VSS, the highest content of proline in comparison with control (+ 73.43%) was related to the ‘K13–40′ on ‘GF677’. The highest MDA (46.50 and 45.29 nmol/gfw) was in ‘Supernova’ and ‘K13–40′ cultivars on the ‘No.32′ rootstock, which increased 76.47% and 75.43%, in the compared to the control, respectively. Drought stress in sensitive rootstock and scion grafted (‘K13–40′ on ‘No.32′), reduced RWC by 44%, also ΨSWP in resistant rootstock and scion grafted (‘Shokoufeh’ on ‘GF677’), WUE increased up to 9 times. In essence, all cultivars, especially ‘Shokoufeh’ grafted on ‘GF677’ rootstock, were more resistant to the VSS in comparison with the grafts of the same cultivars on the ‘No.32′ and ‘GN22’ rootstocks in this study.