Effect of Growth Promoting Bacteria and Salicylic Acid on Melon (Cucumis melo) Seed Germination and Seedling Growth under Salt Stress

Introduction: Using plant growth regulators is one of the methods which can improve plant growth against environmental stresses such as salinity. Salicylic acid plays an important role in the regulation of physiological processes, including germination. Nowadays, the use of growth promoting bacteria is on the rise as it promotes seed vigor, uniformity, germination percentage and brings about better seedling establishment. Growth promoting bacteria can be effective in increasing plant resistance to adverse environmental conditions, which is due to the fact that these bacteria facilitate production of plant hormones such as auxin, GA and cytokinins, and bring about the stabilization of nitrogen or phosphorus availability and other nutrients Materials and Methods: This experiment was conducted as factorial in a completely randomized design with three replications. Salicylic acid factor (SA) was selected at two levels (0 and 1 mM). The bacterial treatments included Azotobacter (AZ), Azospirilum (AZP), complex of Azotobacter and Azospirillum (AZ + AZP), and without inoculation (C) and salinity treatment (S) was considered at five levels (0, 50, 100, 150 and 200 mM). Results: The results showed that none of the treatments had a significant effect on germination percentage. Radicle and plumule length, seed vigor index and seedling fresh weight significantly increased at 50 mM NaCl. Generally speaking, the elongation of plant organs when treated with low concentrations of salts may induce osmotic adjustment activity in plants, which may improve growth. Salicylic acid treatment significantly increased germination rate, Radicle and plumule length and seed vigor index. AZ and AZ+AZP increased germination parameters significantly, compared with the control. Generally speaking, the combination of salicylic acid with AZ better improved germination factors, in comparison to AZP and AZ+AZP. These results are indicative of the synergistic relationship between growth promoting bacteria and salicylic acid. Conclusion: Based on the results, pre-treatment of melon seeds with 1 mM salicylic acid and Azotobacter is suggested to improve seed germination and seedling establishment under salinity stress.