Effects Of Plant Growth Retardants On Growth And Drought Tolerance Of Lolium Perenne

Perennial ryegrass（Lolium perenne L.）is one of high-quality cool-season turfgrass,it plays an important role in protecting and beautifying the ecological environment.However,perennial ryegrass grows so fast,frequent mowing was needed,and the management cost is continuously raised;In addition,its root system is shallower and its drought tolerance is relatively poorer.Studies have shown that plant growth retardants could reduce the mowing frequency of Kentucky bluegrass（Poa pratensis L.）,Tall fescue（Festuca arundinacea Schreb.）,and Bermudagrass（Cynodon dactylon L.）while improving their drought tolerance,but there are fewer studies related on perennial ryegrass there to now.Cultivar“Gentleman”of perennial ryegrass was used as the tested material in this study,three experiments dovetail each other were carried out:（1）Pot experiment:The effects of different concentrations of ethephon,paclobutrazol and chlormequat chloride on the growth characteristics of perennial ryegrass were studied;（2）Hydroponics experiment:Different concentrations of plant growth retardants were used to foliar spraying on perennial ryegrass seedlings under mild,moderate,and heavy drought stress simulated by PEG-6000 to study the response of perennial ryegrass on drought stress.The concentrations of plant growth retardants used which can improve the drought tolerance of perennial ryegrass were screened out by membership function method;（3）Pot experiment:The perennial ryegrass under the natural water control treatment was oversprayed with the top five plant growth retardants screened in the second experiment to explor the effect of overspraying treatment on improving drought tolerance of perennial ryegrass.The main results were as follows:（1）Ethephon,paclobutrazol and chlormequat chloride reduced the total leaf length and the total leaf surface area of perennial ryegrass,thereby reducing the plant height and delaying the growth rate of perennial ryegrass.The total leaf length decreased with the increase of ethephon concentrations and paclobutrazol consistence,the total leaf length decreased significantly by 24.50%and 44.49%compared with the water spraying treatment,respectively under the treatments of 1500 mg·L^-1 ethephon and 800mg·L^-1 paclobutrazol（P<0.05）.（2）Under normal water conditions,the plant growth retardants spraying treatments decreased the total root surface area,total root length,total leaf surface area and total leaf length of perennial ryegrass compared with water spraying.Under drought stress,the total leaf surface area and total leaf length of plants treated with paclobutrazol and chlormequat chloride also decreased compared with those treated with water spraying,but the total root surface area and total root length increased,which could further enhance drought tolerance of perennial ryegrass.（3）The effects of paclobutrazol and chlormequat chloride on the aboveground growth retardation of perennial ryegrass was stronger than that of ethephon,and the effect of improving their drought tolerance was also stronger than that of ethephon.Therefore,when choosing plant growth retardants for regulating the moving frequency of perennial ryegrass,or improving its drought tolerance,the recommended spray concentrations were 500,750,and 1000-fold dilution of chlormequat chloride,100mg·L^-1 and 250 mg·L^-1 of paclobutrazol.（4）Paclobutrazol and chlormequat chloride over-spraying treatments delayed the growth of aboveground part of the perennial ryegrass and promoted the development of the underground roots system under drought stress.The total leaf surface area and total leaf length of perennial ryegrass under over-spraying treatments were significantly lower than those under the single spraying treatments,while the total root surface area and total root length were greater than those under the single spraying treatment disposes.It can be seen that the effect of over-spraying treatments on the growth retardation while promoting the underground root development for perennial ryegrass under drought stress is stronger than that of single spray treatments.（5）Plant growth retardants improved the cellular water physiological state of the perennial ryegrass,increased the content of osmotic regulators in its leaves,and maintained the stability and integrity of plant cell membrane.The effect of paclobutrazol and chlormequat chloride on improving drought tolerance of perennial ryegrass was stronger than that of single sprays,moreover,paclobutrazol and chlormequat chloride played a synergistic role in plant drought tolerance.In the process of maintenance of perennial ryegrass,the recommended over-spring treatments is 750-fold dilution of chlormequat chloride and overs-pray with 250 mg·L^-1paclobutrazol.