Salinity sensitivity and mycorrhizal responsiveness of polyphenolics in ‘Siam Queen’ basil grown in soilless substrate

Abstract The effects of salinity on basil (Ocimum basilicum L. ‘Siam Queen’) phenolic composition was evaluated by exposing plants to either no (Control), low, or moderate levels of salinity induced by NaCl or CaCl2 i n a soilless substrate. Plants in the control and moderate salinity treatments were also inoculated or not with the arbuscular mycorrhizal fungus (AMF), Rhizophagus irregularis (Blaszk., Wubet, Renker, & Buscot) C. Walker & A. Schler. Salinity had no influence on fresh weight (FW) of non-inoculated plants at 41 d, but by 75 d plants treated with salt had lower FW than non-salinized controls. Salinity altered the polyphenolic profile of basil plants by reducing accumulation of several polyphenolics and increasing accumulation of two polyphenolics. In general, the effect of salinity on reducing phenolic accumulation was similar between the two salt types. Non-inoculated plants treated with salt had lower concentrations of caffeic acid (P5), chicoric acid (P7), caffeic acid derivative (P8), and rosmarinic acid (P11) than non-salinized controls at both harvests and lower concentrations of caffeic acid derivative (P1), caftaric acid derivative (P2), cinnamyl malic acid (P3), and feruloyl tartaric acid (P4) at 75 d. Salinity from both salts enhanced accumulation of quercetin-rutinoside (P9) in leaves and stems and CaCl2 also enhanced accumulation of cinnamic acid derivative (P10) in stems. Salinity had a greater influence on minor polyphenolics, particularly at 75 d, when these polyphenolics were more prevalent in non-salinized controls than in plants treated with salt. Inoculation with AMF had no influence on FW at 41 d, but by 75 d increased FW in non-salinized controls and salt-treated plants by ∼10 %. The influence of AMF on specific phenolic concentrations and phenolic profiles varied among harvest dates and salt treatments. In general, AMF inoculation had a greater influence on phenolic concentrations in non-salinized controls at 41 d than at 75 d and in salt-treated plants at 75 d than at 41 d. In salt-treated plants, AMF increased FW and accumulation of several polyphenolics, but did not completely mitigate the negative effects of salinity on FW or phenolic composition. Our results indicate that salinity can alter polyphenolic composition of ‘Siam Queen’ basil even when it has no influence on productivity (FW). While basil productivity may be more sensitive to NaCl than CaCl2 as plants age, the effects of these two salts on polyphenolics were similar. This highlights the importance of considering the effects of salinity and plant age on both crop productivity and quality.