Selection Of Excellent Rootstocks For Cucumber To Resist Calcium Nitrate Stress

Currently,the problem of secondary salinization of facility soil is becoming increasingly serious,seriously affecting the yield and quality of crops.This study used salt sensitive cucumber（Cucumis sativus L.）’Jinchun 4’and 9 types of pumpkin rootstocks as test materials to screen salt tolerant rootstocks.Firstly,the germination of different rootstock seeds under Ca（NO₃）₂stress,the differences in rootstock growth potential during seedling cultivation,and the plant growth after grafting with cucumber were compared and analyzed to select excellent rootstocks suitable for grafting cucumber to cultivate strong seedlings;Then,the rootstock was grafted with cucumber and subjected to Ca（NO₃）₂ stress treatment.Based on the changes in plant growth,photosynthetic fluorescence characteristics,antioxidant capacity,and osmotic regulation ability,a salt tolerant rootstock suitable for cucumber grafting under Ca（NO₃）₂ stress was determined using a multi indicator collaborative evaluation method;Finally,the effects of rootstock grafting on cucumber yield and fruit quality under Ca（NO₃）₂ stress were studied through long-term cultivation experiments.The results of this study will provide theoretical and technical basis for explaining the mechanism of improving cucumber salt tolerance through rootstock grafting and achieving efficient production through facility cucumber grafting cultivation.The main research findings are as follows:Nine pumpkin seeds suitable for cucumber grafting were treated with 0 mmol·L^-1 and80 mmol·L^-1 Ca（NO₃）₂,and the germination differences of various seeds were compared.The results showed that the germination of various rootstock seeds could be inhibited bu Ca（NO₃）₂ stress,while the germination of‘Qianglishi’and‘Qingtengtaimu’rootstock seeds were the best under salt stress,and the salt damage index were much lower,indicating that the potential salt tolerance of‘Qianglishi’and‘Qingtengtaimu’rootstock seeds were stronger.Then,the differences in the growth potential of nine different rootstock plants seedlings were compared and analyzed,and it was found that the seedling emergence rate and growth status of‘Qingtengtaimu’and‘Ribenjingtiantaimu’rootstocks were higher.Further the cucumber plants grafted onto the nine rootstocks,and their growth differences of each grafted plant were analyzied.The results showed that the stem diameter and strong seedling index of cucumber plants grafted onto‘Qianglishi’,‘Genlishen’,and‘Qingtengtaimu’rootstock were higher,the biomass accumulation of‘Qianglishi’and‘Genlishen’rootstock grafted plants was higher,and the survival rate of plants grafted onto‘Qianglishi’,‘Figleaf gourd’,and‘Qingtengtaimu’was higher.Combined with the above results,we screened out that‘Qianglishi’and‘Qingtengtaimu’were excellent rootstocks suitable for cucumber grafting.The self-grafted seedlings of cucumber variety‘Jinchun NO.4’and their grafted seedlings with‘Qianglishi’and‘Qingtengtaimu’rootstocks were subjected to 80 m M Ca（NO₃）₂ stress.The results showed that the malondialdehyde（MDA）content in self-grafted cucumber seedlings under Ca（NO₃）₂ stress was significantly increased,and plant growth and physiology were seriously inhibited.However,the rootstock grafting could increase the activities of superoxide dismutase（SOD）and peroxidase activity（POD）,and the proline and soluble sugar contents,so as to improve the antioxidant capacity and osmomodulation capacity of cucumber seedlings,and alleviate the destruction of Ca（NO₃）₂ stress on the net photosynthetic rate（Pn）,stomatal conductance（Gs）,non-photochemical quenching coefficient（NPQ）,and PSII effective photochemical quantum efficiency（Fv’/Fm’）,finally,alleviated the adverse effects of Ca（NO₃）₂ stress on the growth of cucumber seedlings.The results of the comprehensive evaluation of plant salt tolerance showed that the pumpkin variety‘Qianglishi’was an excellent rootstock suitable for improving the salt tolerance of cucumbers.The self-grafted cucumber seedlings and the rootstock-grafted cucumber seedlings with‘Qianglishi’and‘Qingtengtaimu’were used as the experimental materials.The changes of growth,leaf photosynthetic characteristics,element content,yield and fruit quality of the grafted plants under long-term treatment with 80 m M Ca（NO₃）₂ stress were studied,and the results showed that rootstock grafting could effectively alleviate the inhibition of Ca（NO₃）₂ stress on plant growth,leaf photosynthetic characteristics,yield and fruit element content,and promote the accumulation of photosynthetic pigments in leaves and reducing sugar,soluble total sugar,soluble protein,and soluble solids in fruits.At the same time,the mean fruit weight,single plant yield per plant,area yield,and other yield indicators of cucumber plants grafted onto‘Qianglishi’rootstock under salt stress were significantly higher than those of‘Qingtengtaimu’rootstock grafted plants,whereas the fruit shape index was lower,and the content of vitamin C,N、P、and K elements in its fruit were seriously inhibited.The results indicated that under Ca（NO₃）₂ stress,‘Qianglishi’rootstock grafting was conducive to increasing cucumber yield,while‘Qingtengtaimu’rootstock grafting was conducive to improving fruit quality.Thus,the rootstock could be selected according to actual demand in production.Selection of Excellent Rootstocks for Resistance to Calcium Nitrate Stress in Cucumber:This experiment ultimately evaluated the salt tolerance of grafted cucumber seedlings based on multi index collaborative evaluation.At the same time,combined with the fruit yield and quality traits of cucumber during the fruiting period,it was found that the grafted plants with strong strength rootstocks can better improve fruit yield in production,while the grafted seedlings with green vine rootstocks can better improve fruit quality.