Abstract Background Rosa damascena is a widely cultivated plant in many parts of Iran, due to its ornamental aspects, medicinal properties and essential oil. The efficiency of Ascophyllum nodosum extract (AnE) (0, 2, and 3 g L-1) and Nano-silicon (nSiO2) (0, 50, and 100 mg L-1) in modulating the salinity of two Damask rose genotypes (Chaharfasl and Kashan) was performed under in vitro culture, and some physico-chemical traits of R. damascena explants were measured. Results The results showed that at 100 mM NaCl, the content of relative water content (RWC), membrane stability index (MSI), leaf pigments (Chl b, Chl a, total Chl, and carotenoids), chlorophyll fluorescence parameters, and protein amount were significantly decreased in both genotypes compared to the control conditions. Salinity caused a significant increase in F0 and decrease in Fv/Fm compared to the control conditions in both genotypes. However, the maximum Fm value with a significant difference compared to other treatments was observed in ‘Kashanʼ treated with 3g L-1 AnE + 100 mg L-1 nSiO2 under control conditions. In addition, salinity caused a significant decrease in Fm in ʻKashanʼ and ʻChaharfaslʼ by 22% and 17%, respectively compared to the control condition. ʻKashanʼ had the maximum Fv/Fm compared to the other genotype. The maximum amount of MAD and H2O2 were also demonstrated in saline affected explants. The positive effect of 3 g L-1 AnE + 100 mg L-1 nSiO2 followed by 2g L-1 AnE + 100mg L-1 nSiO2 were considerable. Salinity also increased proline content and the activity of peroxidase (POD), superoxide dismutase (SOD), guaiacol peroxidase (GPX), and catalase (CAT) in both genotypes. AnE at 2 and 3 g L-1 concentration in combination with 100 mg L-1 nSiO2 caused to increase more the activity of the mentioned enzymes. Conclusions The ʻKashanʼ may be more tolerant to salinity by improving water balance, membrane integrity and antioxidant enzyme activity compared to the ʻChaharfaslʼ. The use of nSiO2
