Impact of Salinity on Growth Rate, Physiology, Elemental Composition, and NHX1 Gene Expression of Almond (Prunus dulcis) Cultivars

In almonds (Prunus dulcis), selecting salt-tolerant rootstocks and genotypes is an appropriate breeding strategy. In the present research, we grafted two commercial almond cultivars (‘Sahand’ and ‘TS3’) on the ‘GF677’ rootstock. Then, we monitored the impact of salinity (0.5, 6.5, and 8.5 dS m^-1) on the morphological, physiological, and molecular characteristics of the Sahand and TS3 cultivars. The photosynthetic rate, chlorophyll (a, b and total) content, and carotenoid content decreased with increasing salinity levels in both cultivars, with the least decrease observed in TS3. Under a salinity level of 8.5 dS/m, Sahand exhibited the lowest growth (8.9 cm), leaf area (5412.5 mm²), Chla, Chlb, Chltotal and carotenoid contents (0.58, 0.15, 0.74 and 0.31 mg g^-1FW, respectively). Additionally, Sahand had a Fm/Fv (0.75), N content (1.33%) and Ca, B, Mg, S, Fe and Zn values of 1654.55, 1.64, 395.28, 168.6, 10.35 and 3.05 mg L^-1, respectively. Furthermore, Sahand exhibited the highest MDA level (25.17 nmol g^-1FW), TFC (2.95 mg GA g^−1FW), Na content (649.84 mg L^-1) and Cl content (3.52%).  the lowest TFC (1.75 mg GA g^−1FW) and the highest NHX1 expression, photosynthesis rate (5.65 μmol m^-2 s^-1), gs (0.1 mol m-1 s-1) transpiration rate (6.08 mmol m^-1 s^-1), Ca, S and B content (1903.63, 196.9 and 2.09 mg L^-1, respectively) were belonged to TS3 under 0.5 dS/m salinity. Higher levels of Mg and Fe in the TS3 cultivar resulted in the stablization of photosynthetic pigments. Compared to Sahand, TS3 had a higher nitrogen content, and its greater NHX1 expression was a molecular confirmation of its salt tolerance.