Abstract: Achnatherum inebrians is a perennial bunchgrass of the Poaceae family, widely dispersed in the arid and semi-arid grasslands of northwest China. It forms a reciprocal symbiosis with Epichloё endophyte. The presence of the endophyte provides A. inebrians strong resistance to various stresses, making it more competitive. Both seed germination and seedling growth are important stages of plant growth, determining the future competitiveness of plants. In the present study, a gradient of five different abscisic acid (ABA) concentrations was set up to explore how exogenous ABA affects endophyte-infected (E+) and endophyte-free (E-) A. inebrians seed germination and seedling growth. It was found that the germination rate, embryo length and radicle length of both E+ and E- A. inebrians seeds were significantly promoted when treated with 2.0 mg·L^-1 ABA solution. The net photosynthetic rate, root:shoot ratio, root area, root diameter, root volume and number of roots of the seedlings were higher when treated with 1.0 mg·L^-1 ABA than those in the CK group. In contrast, the germination A. inebrians seeds and seedling growth were inhibited when treated with 4.0 mg·L^-1 ABA solution. These results indicate that the interaction between Epichloё endophyte and an appropriate concentration of ABA improves seeds germination and seedling growth, and enhances the photosynthetic capacity of A. inebrians.

Key words: drunken horse grass (Achnatherum inebrians), Epichloё endophyte, abscisic acid, seed germination, seedling growth