| Drought stress caused by water resources lacking day by day has been becoming an important limiting factor for turf establishment in arid and semi-arid regions of China.Exogenous plant growth regulators have been reported to alleviate drought stress during the period of seed germination and seedling growth.Therefore,using exogenous plant growth regulators to improve the tolerance of seedling turfgrass under drought stress and exploring the mechanism of responses of drought resistance improvement in turfgrass to plant growth regulators foliar spraying are of great significance.In this study,10 Festuca arundinacea cultivars was used as tested materials.Polyethylene glycol(PEG-6000)was used to simulate the mild(10 %),moderate(15 %)and severe(20 %)drought stress by determining the seed germination and seedling growth related indexes of F.arundinacea cultivars,the comprehensive evaluation method was used to evaluate the stronger drought resistance cultivars with component methods.Hydroponics method was used 1/2 Hoagland nutrient solution inoculation with "Red elephant" cultivar which has the strongest drought resistance among 10 tested tall fescue cultivars.Different concentrations of gibberellin(GA),melatonin(MT)and salicylic acid(SA)were foliar sprayed on the 15 % PEG-6000 treated red elephant.Effects of different exogenous hormones’ combination on drought resistance of turfgrass were studied by measuring their morphological and physiological indexes.Finally,the optimal concentration and combination of exogenous hormones were screened to alleviate drought stress.The main results are as follows:(1)Comprehensive evaluation analysis showed that the strongest drought resistance cultivar was "Red elephant",but "Tahuo Ⅵ" appeared the strongest drought resistance under severe drought stress;cultivars with poorer drought resistance were "Barvado","Arid Ⅲ" and "Watchdog",among which "Watchdog" had the largest amplitudes in root indexes variation and appeared the most susceptible to drought stress.(2)Under lighter drought stress,germination potential,germination rate,length of radicle/length of plumule,and root system index of "Red elephant" were significantly higher than those of other cultivars,.Under moderate and severe drought stresses,the root surface area,root length and average root diameter in each cultivar were significantly decreased to a certain extent,indicating that lighter drought stress can promote the seed germination and root growth of F.arundinacea,but effects varied amongst cultivars,while moderate and severe drought stress could inhibit the root growth of plants.(3)Foliar spraying of 0.3 mmol/L GA to F.arundinacea under moderate drought stress,the relative conductivity and MDA content reached the lowest,while the relative water content and proline content of leaves increased significantly;The leaf relative water content,proline content and root system activity increased significantly when 50 μmol/L MT spraying on F.arundinacea leaves;50 μmol/L MT spraying significantly reduced leaf relative electrical conductivity,promoted plant growth and enhanced the drought resistance of seedlings.The proline content and root system activity of F.arundinacea were increased considerably when foliar spraying of 0.5mmol/L SA compared with other concentrations,and the MDA content decreased significantly,all of them were the best spraying concentration.(4)Effect of GA foliar spring on the relative water content of F.arundinacea was more obvious than that of MT and SA.Effect of foliar spring of MT on leaf MDA content and root system activity in F.arundinacea was more clearer than those of GA and SA.Under foliar spring of 50 μmol/L MT,leaf MDA content of F.arundinacea decreased greatly whilst root activity increased the biggest amplitudes;SA foliar spring had a greater effect on the relative conductivity and proline content in F.arundinacea leaves.Compared with drought stress alone,the proline content in F.arundinacea leaves under 0.5 mmol/L SA foliar spring increased the highest amplitude while relative conductivity decreased in the greatest margin.(5)The drought resistance of F.arundinacea can be enhanced by foliar spraying of different combinations of exogenous plant growth regulators.Application of 0.3mmol/L GA first and 50 μmol/L MT following can significantly increase the root surface area,average root diameter,root length and lateral root numbers,improve the ratio of root to shoot and the ratio of dry to fresh biomass,significantly reduce the relative conductivity and MDA content in F.arundinacea,increase the proline content.Comprehensive evaluation results also showed that GA(0.3 mmol/L)+MT(50μmol/L)was the best combination,could effectively alleviate drought stress on F.arundinacea.The results showed that: exogenous plant growth regulators have a good prospect in improving drought resistance of tall fescue in seedling stage,applying a certain concentration of exogenous plant growth regulators can alleviate the damage degree of plants under drought stress and improve the drought resistance of turf grasses;at the same time,the combination of different exogenous plant growth regulators can more effectively alleviate the drought stress of F.arundinacea than singular application of them. |
