Root-promoting Biostimulant Enhances Salinity Tolerance in Wild and Cultivated Rocket Salads

Rocket salads (Diplotaxis spp. and Eruca spp.) are leafy vegetables appreciated for their typical taste and nutritional value. When exposed to salt stress, these plants undergo morpho-physiological and metabolic changes. The aim of the study was to investigate the efficacy of a “root-promoting biostimulant” (Radifarm^®) applied during germination (Experiment 1) and during the growth cycle (Experiment 2) on two rocket species under salt stress. Experiment 1 explored if Radifarm^® can protect seed from salt stress in early-stage development. Different salt levels (0, 150 and 200 mM NaCl) were combined with different Radifarm^® concentrations (0, 0.5, 1, 2.5, 5 mL L^− 1). Experiment 2 investigated how Radifarm^® can promote plant growth after transplantation when irrigated with saline water (0, 150, and 200 mM NaCl) until harvest. Experiment 1 showed that salt stress significantly affected the germination of rocket salads. The addition of Radifarm^® did not improve the germination of D. tenuifolia grown under any salt conditions, but it was beneficial for E. sativa when the highest level of Radifarm^® was applied. In Experiment 2, the application of Radifarm^® significantly reduced the symptoms of salt stress in both species. In E. sativa, salt stress affected all growth parameters (plant height, leaf number and area). However, under 200 mM NaCl, plants fully recovered when Radifarm^® was applied. The same recovery was observed for chlorophyll content in both species. Radifarm^® also contributed to increase protein and lipid content compared to plants under salt stress. This study showed that Radifarm^® was able to protect both species from salt stress.