management strategies are necessary to improve tolerance to water deficit and reduce water consumption in turfgrass. Biside use of tolerant cultivars, we can mention the use of plant growth regulators and the endophytic fungi, which help the plant in adjusting the drought stress. Growth regulators such as trinexapac-ethyl (TE) play an effective role in reducing growth in turfgrass management. Furthermore, the presence of the endophyte fungus (Epichloe), in grass cultivars can effectively improve the host plant's tolerance to adverse environmental conditions. Therefore, the present study was conducted to investigate the single and combined effect of the growth retarder of trinexapac-ethyl and the presence of endophytic fungi in increasing the tolerance to drought stress of the native species of tall fescue.The experiment was carried out as a factorial (2×2×2) in four repelication in greenhouse conditions. The treatments included the presence of endophyte in the turfgrass (endophyte-free (E−) and endophyte-infected (E+) clones), TE at two levels (control and 1.95 ml/L) and drought stress including two levels (full irrigation and withholding irrigation). During the experiment, various growth parameters, quality of turfgrass, physiological and biochemical traits of turfgrass were eva‎luated in response to drought stress. The results showed that drought stress caused morphological, biochemical and grass quality changes in tall fescue under stress condition. However, the response of turfgrass containing and free of endophyte and turfgrass treated with trinexapac-ethyl was different to drought stress.The application of trinexapac-etyl, while reducing growth rate of shoot in non-stressed conditions, improved the growth of roots and reduced the leaf firing, ion leakage, malondialdehyde and hydrogen peroxide levels at withholding irrigation compared to the control. Treatment with trinexapac-ethyl increased the activity of antioxidant enzymes in both endophyte-free and endophyte-infected plants under drought stress. However, the reduction of malondialdehyde and hydrogen peroxide, as well as the improvement of antioxidant enzyme activity under drought stress, in the endophyte-infected turf treated with TE was higher compared to endophyte-free plants. The presence of endophytic fungi also increased the biomass of the host plant in normal irrigation and also decreased the amount of stress indicators such as ion leakage and malondialdehyde in the host plant. In addition, the positive effect of the presence of endophyte fungi accompanied by TE application increased the root growth parameters and days to 90% leaf firing under drought stress conditions. Based on the results of PCA analysis, visual quality of the turfgass, the turf color and the relative water content had a negative relationship with the ion leakage, the amount of malondialdehyde, hydrogen peroxide and the percentage of leaf firing, and un-treated endophyte-free tall fescue were in the vicinity of these vectors, indicating less tolerance to drought stress in these grasses. Furthermore, E− and E+ clones treated with TE exhibited high antioxidant enzymes activites, better visual quality and root growth compared to untreated plants under drought stress conditions. Based on the obtained results, the application of TE and the presence of endophytic fungi can effectively improved drought tolerance and recovery in tall fescue by improving root growth activity of antioxidant enzymes and mitigated the harmful effects of drought on the quality and physiology of turfgrass. Finally, according to the results of this experiment, the use of TE had a synergistic effect with the endophyte fungi to alluviating drought stress on tall fescue, resulted in more tolerance of endophyte-infected clone to drought stress

نعمت اله اعتمادي شلمزاري

رحيم اميري خواه , محمدرضا سبزعليان دستجردي

مهديه غلامي , پرويز احسان زاده