Abstract: This greenhouse experiment studied the effects of different concentrations of salicylic acid (SA) on endophyte-infected (E+) and endophyte-free (E-) perennial ryegrass (Lolium perenne), under continuous drought stress for 15 days or well watered (Control). Measurements included leaf relative leaf water content, chlorophyll content, peroxidase (POD) activity, superoxide dismutase (SOD) activity, malondialdehyde (MDA) content, proline (Pro) and soluble sugar (SS) of the perennial ryegrass. Changes in physiological indices such as SS content were examined to determine the effects of SA and endophytic fungi on perennial ryegrass under drought stress. It was found that the relative water content, chlorophyll content, POD activity and SS content of E+ were significantly higher (P<0.05) than those of E- L. perenne plants under drought stress. The addition of exogenous SA increased the relative water content, chlorophyll content, POD and SOD activities, and Pro and SS contents, while decreasing MDA content. The present study showed that exogenous SA solutions of 0.25 and 0.50 mmol·L^-1 were best for enhancement of the drought tolerance of L. perenne. There was a significant (P<0.05) interaction effect between Epichloё endophyte and SA together on SOD activity, POD activity and chlorophyll content of perennial ryegrass. In summary, Epichloё endophyte and SA both improved the drought resistance of perennial ryegrass. Specifically, Epichloё endophyte and SA promoted osmotic adjustment and activity of oxygen radical scavenging system, and thereby increased the drought resistance of the host plant.

Key words: perennial ryegrass, Epichloё, salicylic acid, drought stress