Pathogen resistant advantage of endophyte-infected over endophyte-free Leymus chinensis is strengthened by pre-drought treatment

Symbiotic relationships with beneficial microbes often increase the resistance of the host grass to abiotic and biotic stresses. In this study, the resistance of endophyte-infected (E+) and endophyte-free (E-) Leymus chinensis to two species of pathogen fungi, Curvularia lunata and Bipolaris sorokiniana, were compared under normal water and pre-drought treatments. The results showed that endophyte infection significantly reduced leaf lesion area of the host grass on one hand, and on the other hand the maximum quantum efficiency of PSII (Fv/Fm) of E+ plants was higher than E- plants, and these advantages of E+ over E- plants were strengthened by pre-drought stress. Pre-drought treatment led to significantly higher salicylic acid (SA) and lignin accumulation in E+ plants in comparison with E- when exposed to both C. lunata and B. sorokiniana. Additionally, glutamine and phenylalanine concentrations were significantly affected by the interaction between endophyte infection and pathogen inoculation. Overall, endophytes could enhance the pathogen resistance of host by activating a rapid defense reaction of the plant, and this advantage of E+ over E- plants could be strengthened by pre-drought treatment.