Document Type : Research paper


Research Institute of Forests and Rangelands, Agricultural Research, Education and Extension Organization (AREEO), Tehran, Iran



Besides plant strategies to mitigate drought stress effects, the application of beneficial rhizobacteria may enhance plant tolerance. This study aimed to assess the ability of phosphate-solubilizing bacteria (PSB) to improve the growth and physiology of Achillea santolina (Santalin yarrow) under drought stress. The interaction effects of PSB (Pseudomonas fluorescens isolates FRPF4, FRPF6, and FRPF12) (at 107 CFU/ml) and drought stress (30, 50, and 80% field capacity) were studied as a factorial test based on a completely randomized design under greenhouse conditions (n=3; P<0.05). Several vegetative and physiological parameters were measured at the full flowering stage. The growth factors included plant shoot height, canopy diameter, root length, and wet and dry weights. The results revealed a significant decrease in all the growth parameters under drought stress. However, PSB isolates, especially FRPF4, significantly moderated the stress negative effects on vegetative factors. Drought stress also significantly increased the total soluble sugars (TSS), free proline, total flavonoids (TF), and DPPH contents of the Santalin yarrow leaves. Drought-stressed plants inoculated with the PSB isolates showed a significant reduction in free proline and DPPH concentrations. However, the TSS and TF contents elevated in the stressed plants treated with PSB isolates. Carotenoid, chlorophyll a, b, and total chlorophyll contents also decreased in the stressed plants. However, the levels of these factors increased in the plants treated with PSB isolates in response to water deficit stress. Thus, PSB isolates may mitigate the adverse effects of drought stress on Santalin yarrow plants through several direct and indirect mechanisms.