Effects Of Exogenous Substances On Seed Germination And Chilling Resistance Of Pepper Under Low Temperature Stress

Pepper（Capsicum annuum L.）,originated from the tropical regions of Central and South America,is akind of thermophile vegetable crop,also an important vegetables of autumn and winter cultivation ingreenhouse,so the cultivated area was expanding in China in recent years.Anti-season vegetable cultivationin North China were not heated in solar greenhouses and plastic greenhouses,often facing long suboptimaltemperature or short critical low temperature,seriously affected the pepper production,low temperature wasa major limiting factor during pepper cultivation,therefore,improving cold resistance of pepper has becomea urgency in theoretical research and practical production.Study on plant stress resistance induced byexogenous substances had achieved considerable success,providing a solid theoretical foundation for plantsresistant to chemical control technologies.Pepper(Xinjiao NO.3and Zhudachang) seeds and seedlings werechose as experimental material and the low temperature conditions were smulated with illuminatingincubator,different concentration of spermidine,chitosan,salicylic acid,CaCl2,betaine,trehalose solutionwere soaked and sprayed respectively,this reseash made a comparison to the effects of those exogenoussubstances on cold resistance of pepper seed and seedling,providing theoretical basis and technicalguidance for culture of pepper seedling under low temperature in winter and spring in Xinjiang.The mainresults of this study were as follows:1. In a certain range of concentrations,exogenous spermidine,chitosan, salicylic acid,CaCl2,glycinebetaine,trehalose solution could variously promote seed germination by increasing seeds germinationpotential,germination rate,germination index,and vitality index of pepper seeds under low temperaturestress.The optimal concentration of these six kinds of substances to promote seeds germination of pepperwere0.1mmol/L,100㎎/L,0.5mmol/L,10mmol/L,5mmol/L,0.5mmol/L.Spermidine and chitosan treatmentare more effective than CaCl2,trehalose,salicylic acid and glycine betaine treatment.2. The optimal concentration of exogenous spermidine,chitosan,salicylic acid,glycinebetaine,CaCl2,trehalose to promote pepper seedling growth under low temperature stress as same as seedgermination,but they had different mechanism.Among them,spermidine and glycine betaine mainlypromote the root growth by affecting root length,root fresh weight,root dry weight;CaCl2mainly promotethe shoot growth by affecting seedlings height,shoot fresh weight,shoot dry weight;chitosan,salicylic acidand trehalose had positive effects on whole-plant growth.3. Different concentration of spermidine,chitosan,salicylic acid,CaCl2,glycine betaine,trehalose couldproduce positive influence on improving cold resistance of pepper seedlings by reducing relativeconductivity,chilling injury index,accumulation of MDA and increasing the soluble sugar content andproline content under low temperature stress.The optimal concentration of six kinds of substances toimprove chilling resistance of pepper were0.5mmol/L,50㎎/L,2mmol/L,10mmol/L,10mmol/L,10mmol/L,having differences with the induced concentration of seed germination and seedlinggrowth.Spermidine,chitosan,salicylic acid and glycine betaine treatment were more effective than CaCl2and trehalose treatment.4.0.5mmol/L spermidine,50㎎/L chitosan,2mmol/L salicylic acid,10mmol/L betaine could producepositive influence on improving pepper seedlings growth and enhancing the cold resistance of pepperseedlings by increasing seedling height,stem diameter,root fresh weight,root dry weight,shoot freshweight,shoot dry weight under low temperature stress.The accumulation of fresh material and dry matterfrom the roots of pepper seedlings plays an important role on accelerating the seedling growth and promoting the breeding healthy under low temperature stress.5. With the increase of stress time,the content of soluble sugar,soluble proteins,proline and MDA inpepper seedlings leaves increased,SOD and POD activity increased at first and then decreased,chlorophyllcontent declined.During the low temperature recovery process,osmotic substance and MDA content weredecreased,SOD and POD activity,chlorophyll content staged a recovery.0.5mmol/L spermidine,50㎎/Lchitosan,2mmol/L salicylic acid,10mmol/L glycine betaine could significantly reduce MDA content andlower the speed of MDA increasing,and improve the soluble sugar,soluble protein,proline and chlorophyllcontent,enhance SOD and POD activity under low temperature,improve cold resistance of pepperseedlings.The effect of four kinds of substances were spermidine>chitosan>glycine betaine>salicylic acid.6. The soluble sugar content,soluble protein content,SOD activity,POD activity and chlorophyllcontent of pepper seedlings leaves were very significantly positive correlated with the chilling resistanceindex,proline content was significantly positive correlated with the chilling resistance index,it wasindicated that there has a close relationship between cold resistance of pepper seedlings treated byexogenous substances and chlorophyll content,protection enzyme activity,osmotic substance content,so wecould determin the effect of exogenous substances on chilling resistance of pepper seedlings byidentificating these indicators.7. The result indicated that six kinds of exogenous substances had positive effect on enhancing chillingresistance of pepper through analyzing morphological indexex and physiological indexes in germinationstage and seedling stage under low temperature stress synthetically,the effect of spermidine and chitosanwere more significant than other substances.