Water scarcity is a major constraint that adversely affects plant development and growth. Abscisic acid (ABA) is a plant stress hormone that is rapidly synthesized and can induce stomatal closure to conserve water, thereby alleviating the drought stress of plants. The Epichloë endophyte enhances the drought tolerance of Achnatherum inebrians (drunken horse grass, DHG). To better understand how the Epichloë endophyte enhances drought tolerance, DHG plants without (EF) and with (EI), an Epichloë endophyte, were grown under 20% and 60% soil water conditions (SWC), and the leaves of the three treatments of EF and EI plants were sprayed with ABA solution (1 mg/L); fluridone (FLU), the ABA biosynthesis inhibitor solution (1 mg/L); and distilled water, respectively. Four-weeks later, the results indicated that the exogenous ABA application promoted plant growth, stomatal conductance, and photosynthetic rate, while the opposite effect occurred with plants sprayed with FLU. The differences between EI and EF plants in tiller number, height, chlorophyll content, stomata conductance, and photosynthetic rate were highest when sprayed with ABA. Thus, it is concluded that ABA might be involved in the moderating effect of Epichloë endophytes on DHG plants exposed to drought by maintaining growth and improving photosynthetic efficiency.

The present study explored the effects of an Epichloë endophyte on growth and physiology parameters of drunken horse grass (DHG, Achnatherum inebrians) under four different soil water content. The possible transgenerational effects (TGE) on the above-mentioned indicators were examined. DHG plants with (EI) and without (EF) this Epichloë endophyte, grown from seed of plants from the same seed line, were used. The seeds had originated in the relatively dry site at Yuzhong [YZ(D)], and also used were seed of plants from this original seed-line grown at the relatively wet site Xiahe [XH(W)]. The growth, photosynthesis, phytohormones, and elements were measured. This study showed that the endophyte increased the aboveground biomass and chlorophyll content, with the increasing of photosynthetic parameters. The presence of endophyte also significantly promoted abscisic acid and indolE−3-acetic acid content but decreased the cytokinin content. The nitrogen and phosphorus content of EI plants was significantly higher than that of EF plants, but the endophyte decreased ratios of C:N and C:P at drought condition. In addition, TGE were present, affecting host growth and the above-mentioned parameters, and which indicated that the plants grown from the seeds in YZ(D) site are more competitive than those in the XH(W) site under water deficiency conditions.