The Differences In Tolerance Of Hemp Varieties To Neutral And Alkaline Salt Stress

The soil salinization restricts the development of agriculture and economy,which has become a global problem.How to ameliorate and utilize the saline soils is a very important scientific matter to be solved urgently.Hemp(Cannabis sativa L.)is an annual dioecious herb with strong abiotic resistance,wide environmental adaptability and other biological characteristics so could be a potential candidate crop grown in saline-alkali soils.Five hemp varieties,Yunma 1,Yunma 5,Yunma 7,Wanna 1 and Bama Huoma,were used as materials in this study.Salt stress was simulated by neutral salt NaCl and alkaline salt Na2CO3.The germination stage and seedling stage of these five varieties were treated with salt stress under different culture conditions.The aims of this study were to explore the semi lethal concentration of salt tolerance in the germination stage and seedling stage,and evaluate five varieties of hemps' salt tolerance evaluation in germination and seedling stages base on growth indexs and physiological indexs such as seed germination rate,germination potential,radicle length,hypocotyl length,plant height,stem diameter,SOD activity,MDA,proline,soluble sugar content and so on.To explore the effects of different concentrations of salicylic acid,glucose and ascorbic acid on the seed germination of Yunma 1 under semi lethal concentration of salt tolerance,and to determine the optimal concentration and the best combination of the three kinds of exogenous compounds.The results were as follows:1.Alkaline salt inhibited the seed germination evidently more than neutral salt.Under NaCl(0,85,170,255,340mM)and Na2CO3(0,50,100,150,200 mM)stress,the relative germination rate,germination potential,germination index,vigor index,radicle and hypocotyl growth of hemp seeds were inhibited,and decreased with the increase of salt concentration,but under 85mM NaCl treatment the hypocotyls growth of Yunma 5 and Wanma 1 were promoted.The seed salt injury indexs of hemp varieties were increased with the increase of salt concentration for the both salts.Under Na2CO3 stress,radicle and hypocotyls of seed became soft and rotten,the inhibition of seed radicle and hypocotyl growth was greater than that of NaCl stress.2.There was an association between the semi lethal concentration of salt and salt tolerance at germination stage.The NaCl salt tolerance of five varieties at germination stage was sorted from high to low according to the ruembership function values as Yunma 7>Yunma 1>Yunma 5>Wamna 1>Bama Huoma,sorted according to the semi lethal concentration of NaCl as Yunma 1(232mM)>Yunma 7(220 mM)>Yunma 5(215mM)>Wanma 1(208mM)>Bama Huoma(203mM).Under Na2CO3 stress,the order of salt tolerance from high to low was Yunma 5>Yunma 1>Yunma 7>Bama Huoma>Wanma 1,while the semi lethal concentration of Na2CO3 was Yunma 5(161mM)>Yunma 7(132mM)>Yunma 1(130mM)>Wanma 1(120mM)>Bama Huoma(113mM).3.Under NaCl(0,130,260,390,520mM)and Na2CO3(0,80,160,240,320mM)stress growth of hemp seedlings were inhibited evidently.The plant height,stem diameter,leaf area and root shoot ratio of hemp seedling showed a downward trend with the increase of salt concentration,significantly different from the control.The salt-injury index and salt-injury rate of hemp seddlings rose with the increase of salt concentration.Only a small number of plants showed salt injury symptoms under treatment of low concentration salt,but almost all hemp seedlings showed salt injury symptoms under stress of high concentration salt with over 80%of salt-injury rate.The semi lethal concentration of NaCl to hemp seedlings of the tested varieties was estimated as 520mM or more,and that of Na2CO3 was 260mM?320mM.4.NaCl and Na2CO3 stress differently influenced the physiological indexes of hemp seedlings.Leaf relative conductivity,SOD activity,proline and soluble sugar content increased gradually with the increase of salt concentration,while the soluble protein decreased,although MDA changed irregularly under stress of the two salts.The NaCl salt toleranee of five varieties at seedling stage was sorted from high to low according to the membership function values as Yunma 1>Yunma 7>Wanma 1>Bama Huoma>Yunma 5,while the tolerance to Na2CO3 stress in order as Yunma 7>Bama Huoma>Wanma 1>Yunma 1>Yunma 5.5.Separately use of salicylic acid,glucose or ascorbic acid promoted seed germination parameters such as germination rate,germination potential,germination index,vigor index,hypocotyl length and radicle length of Yulma 1 under salt stress of semi lethal concentration(NaCl 232mM,Na2CO3 130mM).The optimal concentrations of salicylic acid,glucose ascorbic acid for alleviating NaCl stress were 1.45mM,1.67mM and 1.70mM,while for alleviating Na2CO3 stress were 2.17mM,1.67mM and 2.27mM.For pairwise uses,the germination percentage,germination index and vigor index,radicle length and hypocotyl length were improved best under stress of NaCl when salicylic acid and ascorbic acid combined.Under stress of Na2CO3,germination percentage,germination index and vigor index were the highest when glucose and ascorbic acid combined.But all of pairwise uses inhibited the radicle growth of hemp Yunma 1.