Effects Of Grafting And Exogenous NO On Chilling Tolerance Of Bitter Gourd Seedlings

Bitter melon(Momordica charantia L.)is an important vegetable in South China.With the recognition of the edible and medicinal value of bitter gourd,the cultivation area has been expanded year by year.Bitter gourd is resistant to heat and light,but it often suffers from continuous low temperature and weak light in winter,which results in lower yield.Grafting and applying exogenous NO are effective and simple ways to overcome the effect of low temperature on the growth of bitter melon.1.In order to improve the cold resistance of bitter melon,and screen the rootstock with good cold resistance,towel gourd and Pumpkin,a total of five varieties,were used as grafting stocks in this experiment.Bitter melon,Cuiliu No.2,was employed as the scion varieties,using scion-root seedling and self-grafted Cuiliu No.2 as the control,under the day/night 8? low-temperature stress to study the effect of cold resistance the grafted on different rootstocks.The main results are as follows in the study:(1)The grafting survival rate of 5 stock varieties was compared.The graft survival rate of bitter rootstock No.2 was highest,followed by Gen Wudi and Zhongyuan Gongrong,and the survival rate of bitter rootstock No.1 was lowest.The results showed that the rootstock stock,bitter rootstock No.2,Gen Wudi and Zhongyuan Gongrong had good affinity with the Cuiliu No.2.The survival rate of nurse grafting is slightly better than that of cuttage grafting,but it has the disadvantages of complicated steps and low efficiency.And cuttage grafting in the environmental humidity requirements for grafting is very high.Therefore,in consideration of this study,nurse grafting is used.(2)Grafted seedlings on the ground and underground part growth,root activity,and growth rate were higher than the control under low temperature stress.Especially Zhongyuan Gongrong,Bitter rootstock No.2,and Root invincible of pumpkin rootstock grafted seedlings performed well,and were significantly higher than the control;Grafted seedlings' chilling injury index were lower than the control,which chilling injury index of Zhongyuan Gongrong,Bitter rootstock No.2,and Root invincible grafting seedlings was significantly lower than that of the control.This showed that grafting can significantly improve chilling tolerance of bitter gourd seedlings,and reduce the effect of low temperature stress.It indicated that the growth vigor and cold resistance of five varieties of rootstock grafted seedlings were superior to the control,the comprehensive features of Zhongyuan Gongrong,Bitter rootstock No.2 and Root invincible were excellent to be taken as the cold resistant rootstocks on bitter melon on production.(3)Balsam pear Seedlings Grafted under low temperature stress,chlorophyll a,carotenoid and total chlorophyll increased significantly than the control,but the chlorophyll b variation of grafted plants under low temperature reduced the chlorophyll a,total chlorophyll,carotenoid pigment degradation,but not influence on chlorophyll b.Grafting could improve photosynthetic index and fluorescence index of balsam pear leaves under low temperature stress,which was beneficial to delaying the decline of photosynthetic capacity caused by chilling at leaves.(4)Grafted seedlings can reduce the relative electrical conductivity;decrease content of MDA,H2O2 and O2-·;raise the content of GSH,ASA,soluble sugar,soluble protein and proline;improve the activities of POD,SOD,PPO,PAL,DHAR,GR,APX and CAT of the bitter melon seedlings under low-temperature stress to reduce the harm of low-temperature.It indicated that grafted seedlings could enhance the bitter melon seedlings'adaptability for low temperature stress through improving the activities of defensive enzymes;increasing the osmotic adjustment substance contents;reducing membrane lipid peroxidation and protecting the stability of cell membrane structure.2.In this experiment,the Bilv bitter melon variety was taken as test material,different concentrations of sodium nitroprusside(SNP)(0.00,0.10,0.50,1.00,1.50 and 2.00 mmol·L-1)was employed as exogenous nitric oxide(NO)donor to process bitter melon seedlings under 8? low-temperature stress to study the internal mechanism of exogenous NO improving the cold resistance of bitter melon.The results showed that the treatment of SNP increased the leaves relative water content,total chlorophyll,chlorophyll a,chlorophyll b and soluble protein content;Plant height,stem diameter,leaf area and root volume increased than control,and the cold resistance of bitter melon seedlings in field was improved.The treatment of SNP could improve plant height/stem diameter and leaf area/root volume;reduce the relative electrical conductivity and content of MDA;raise proline content and the activities of POD,SOD and CAT of the bitter melon seedlings under low-temperature stress to reduce the harm of low-temperature.It was also found that the cold resistance effect of treatment with low concentration of SNP is bitter than the high's,especially the treatment with 0.50 mmol·L-1 SNP is the best.It indicated that the exogenous NO with proper concentration could promote the plant growth,soluble protein content,relative water content and chlorophyll content to enhance the bitter melon seedlings' adaptability for low temperature stress,through improving the activities of defensive enzymes,increasing the osmotic adjustment substance contents,and reducing membrane lipid peroxidation and protecting the stability of cell membrane structure.