Biochemical, physiological and antioxidant enzymatic activity responses of pistachio seedlings treated with plant growth promoting rhizobacteria and Zn to salinity stress

Soil salinity and Zn deficiency are among the major limiting factors for growth and improvement of pistachio trees in central Iran. Using plant growth promoting rhizobacteria (PGPR) is new strategy to reduce the destructive effects of salinity and improvement of nutrient availability. This study investigated the individual and the interactive effects of the PGPR and Zn treatments on some physiological and biochemical parameters, antioxidant enzymes activities and alleviation of salinity stress in pistachio seedlings. The treatments include isolates of fluorescent pseudomonads as PGPR [control (non-inoculated), pf1, pf2 and pf3], Zn (0 and 5 mg kg−1 soil) and salinity (0, 1000 and 2000 mg NaCl kg−1 soil). The results indicated that salinity increased the proline, soluble sugars and H2O2 concentrations in the seedling leaves and roots. Inoculation with PGPR efficiently enhanced the concentrations of proline (35 and 16 %) and the soluble sugars (25 and 22 %), whereas, reduced the H2O2 levels (16 and 18 %) in the leaves and roots. Increasing the concentration of NaCl to 2000 mg kg−1 significantly decreased the dry weight, Zn concentration, and chlorophyll and carotenoids contents. At the same salinity level, the PGPR and Zn alone increased these parameters compared to the untreated soil, but furthest by the combined PGPR and Zn treatments. Also, the combined application of PGPR and Zn significantly increased the antioxidant enzyme activities and protein concentration relative to their sole usage in the pistachio seedling leaves and roots, especially at the higher salinity levels. The isolates containing ACC-deaminase activity were more efficient to alleviate salt stress and develop seedling improvement.