Alleviation Of Drought Stress During The Germination And Seedling Stages Of Hemp(Cannabis Sativa L.) By Using Exogenous Substances

Hemp（Cannabis sativa L.）,an annual herbaceous plant belonging to genus Cannabis,family Cannabaceae,has extremely high values of comprehensive utilization.As a kind of abiotic stress,drought affected the growth of hemp.Exogenous substances may alleviate the drought damage to hemp and improve the ability to drought resistance of hemp.In this study,two hemp varieties（Yunma 1 and Bamahuoma）were chosen as the research materials.At the germination stage,we used the filter paper culture method to study the alleviating effect of soaking with different exogenous substances on hemp seeds under drought stress（simulating by 20%PEG-6000）.In the pot experiment by the weighing water controlling method,the alleviating effects of spraying different exogenous substances on hemp seedling under drought stress was studied at seedling stage.The related morphological and physiological indicators were determined to study exogenous substances for the drought resistance of hemp and its comprehensive evaluation was using membership functions.The main results are as follows:1.Soaking seeds with gibberellin,Vc,glucose,glycine betaine and CaCl₂ at a certain concentration can alleviate the seed germination of Yunma 1 and Bamahuoma under drought stress in different degrees.For Yunma 1,the appropriate concentrations are 400-600mg/L,800mg/L,600mg/L,800mg/L,and 400mg/L;The suitable treatment concentration of Bama hemp is 400-600 mg/L,800 mg/L,400-600 mg/L,800 mg/L and400 mg/L.Gibberellin and Vc treatments were better in the relieving effects of five exogenous substances on the drought stress.2.Drought stress（20%PEG-6000）has a significant inhibitory effect on the physiology of hemp seedlings in the early stages of germination.Soaking seeds with appropriate concentrations of gibberellin and Vc can increase the drought tolerance of germination seedling of hemp under drought stress.The soluble protein and soluble sugar content increased in the germination seedlings of hemp fter soaking seeds with gibberellin and Vc,and the peroxidase（POD）activity and superoxide dismutase（SOD）activity were also significantly increased.Evaluated by the membership function,Yunma 1 had the best physiological performance when seeds were soaked with 600mg/L gibberellin and 400 mg/L Vc under drought stress respectively.While,seeds were soaked with 600 mg/L gibberellin and 600 mg/L Vc respectively,the drought resistance of Bamahuoma was stronger.And the gibberellin treatment was better than Vc.3.Drought stress severely inhibits the growth of hemp seedlings.As a short growth time after treatment,the effect of different exogenous substances on the growth indicators of Yunma 1 and Bamahuoma were not obvious.For different hemp varieties,the appropriate concentration of exogenous substances was different.The suitable spraying concentration for Yunma 1 is Vc 500mg/L,CaCl₂ 500mg/L,glycine betaine200mg/L and gibberellin 200mg/L respectively.The suitable concentration for Bamahuoma is Vc 800mg/L,CaCl₂ 800mg/L,glycine betaine 1200mg/L and gibberellin1200mg/L.At these concentration treatments,the values of whole plant weight on the ground,seedling height and stem diameter are all good.4.After spraying suitable concentrations of Vc,glycine betaine,CaCl₂ and gibberellin respectively under drought stress,the osmotic adjustment substances of hemp accumulated significantly,and antioxidant enzyme activity also increased significantly.It can be known from the membership function evaluation,the drought resistance is good when Yunma 1 was sprayed with 500 mg/L Vc and CaCl₂,and 200mg/L glycine betaine and gibberellin respectively,the mitigation effects of the four exogenous substances were Vc>CaCl₂>gibberellin>glycine betaine.Spraying 800mg/L Vc and CaCl₂,and 1200mg/L glycine betaine and gibberellin respectively,it can relieve the drought damage to the seedlings of Bamahuoma effectively,the alleviating performance were CaCl₂>glycine betaine>gibberellin>Vc.