Evaluation of Response of Growth and Physiological Factors of Barberry (Berberis vulgaris L.) Inoculated With Plant Growth-Promoting Rhizobacteria to Salinity of Irrigation Water

 Barberry is one of the important agricultural products of Iran and has an important role in the economy of farmers, especially in South Khorasan province. Salinity as abiotic stress can cause an ionic or osmotic imbalance in plant cells. Salt stress also restricts plant growth and development by affecting water reducing availability and affecting plant production. Despite the relatively high tolerance of barberry to environmental stresses, increasing soil salinity and irrigation water in barberry growing areas, the growth, and yield of this agricultural product have decreased. The use of plant growth-promoting rhizobacteria (PGPR) is a new method that has been shown to increase the tolerance of various plants to salinity stress.

 Due to the lack of information about the effect of salinity on the growth and establishment of barberry off-shoot and the role of beneficial soil bacteria in increasing the tolerance of this plant to salinity stress, this study aimed to investigate the role of bacteria on growth, physiological and biochemical properties and uptake of nutrients by barberry off-shoot at different levels of irrigation water salinity. For this purpose, a factorial study was conducted in a randomized complete block design with 3 replications. Experimental factors included plant growth-stimulating bacteria at three levels (control (Without inoculation) and inoculation with Pseudomonas sp. P1 and Pseudomonas sp. P2) and salinity of irrigation water at three levels (control, 6 and 12 dS/m from sodium chloride source). The bacteria used in this study were able to produce indole acetic acid, siderophore, ACC deaminase enzyme, and dissolve insoluble phosphate (tricalcium phosphate) in vitro. For inoculation, inoculum containing each bacterium with a population of 108 cells/ml was prepared in the Nutrient Broth medium and added to the root medium. The plants were irrigated with non-saline water for one month and then with saline water for two months based on experimental treatments. Finally, leaf sampling was performed and various characteristics such as leaf dry weight, chlorophyll, proline, total sugar, RWC and phosphorus, potassium, sodium, and chloride concentrations were measured. Analysis of variance of traits was performed using SAS software and the means were compared using the LSD method with a probability level of P≤0.05.

 The results showed that the salinity of irrigation water reduced leaf dry weight, chlorophyll and carotenoid concentration, relative water content, and potassium to sodium ratio of barberry leaves. Decreased photosynthetic pigments under salinity may be due to decreased synthesis of the main chlorophyll pigment complex, oxidative damage to chloroplast lipids, pigments, and proteins, or increased chlorophyllase activity. In contrast, with increasing salinity, the amount of proline and total sugar and the concentration of phosphorus, sodium, and chlorine in leaves increased. Bacterial inoculation also increased leaf dry weight, chlorophyll, carotenoids, potassium concentration, relative water content, and potassium to sodium ratio, especially in saline conditions. Also in saline conditions, the concentrations of sodium, chlorine, phosphorus, proline, and total sugar in the leaves of barberry off-shoot inoculated with bacteria decreased. It seems that PGPR plays a significant role in the regulation of cellular osmolites, including proline and soluble sugars, by producing various metabolites and increasing the absorption of water and nutrients. The highest amount of leaf dry weight (0.70 g), total chlorophyll (0.92 mg g-1 fresh weight), carotenoids (0.51 mg g-1 fresh weight), leaf potassium (0.48 %), and total leaf sugar (43.7 mg g-1 dry weight) was obtained from the application of PGPR in conditions without salinity stress. Also, the use of bacteria in saline conditions decreased the amount of phosphorus and total sugar and in non-saline conditions increased the amount of these parameters. PGPR through various mechanisms such as the production of auxin, organic and mineral acids, and secretion of proton and phosphatase enzymes increase the availability of phosphorus for the plant, root growth, and absorption of water and nutrients. Increased absorption of water and nutrients has led to increased leaf growth and development and therefore reduced phosphorus concentration (dilution effect).

 According to the results, PGPR by increasing the absorption of water and nutrients such as phosphorus and potassium caused osmotic regulation in the plant and thus increased the tolerance of barberry off-shoot to salinity stress of irrigation water. The ability of these bacteria to improve plant growth in saline conditions could be due to the production of auxin, siderophore, dissolution of tricalcium phosphate, and especially the production of the enzyme ACC-deaminase (as observed in vitro). Therefore, these bacteria can be used to improve the nutrition growth and establishment of barberry off-shoot.