Salinity is one of the most important factors causing stress damage to the growth and metabolism of plants. Various biostimulants have been used to increase plant tolerance to salinity stress, which seaweed extract providing promising improvements on plant performance. It is necessary to investigate the effects of salinity stress on agricultural products and especially on rice cultivation. Therefore, in this study, the effects of Nizamuddinia zanardinii brown algae extract on the morphophysiological characteristics of rice plants under salt stress were investigated. Stress conditions were created for rice plants with concentrations of 100 and 150 mM of sodium chloride salt. Then, concentrations of 25, 50 and 100% of the extract of one gram per liter of brown algae were used to evaluate the growth indicators. The results showed that salinity treatment decreased hypocotyl height, radicle length and seedling weight compared to the control, and simultaneous salinity and extract treatment led to improvement of growth parameters. The highest amount of hypocotyl height, radicle length and seedling weight was observed in simultaneous treatment with 50% extract and salt concentrations. The hypocotyl height and seedling weight increased by 28% and 13% in 100 mM salinity which was treated with 50% extract, and 125% and 27% in 150 mM salinity which was treated with 50% extract, respectively. The radicle length also increased by 32% in 150 mM salinity which was treated with 50% extract. The results indicate that Nizamuddinia zanardinii extract can be effective in improving rice plant growth under salt stress.
