Study On The Mechanism Of Grafting Improving Disease Resistant Of Root Rot And Bacterial Wilt In Pepper

Pepper(Capsicum annuum L.)is one of the important vegetables grown in solargreenhouse.Now,the soil-borne diseases,such as root rot,bacterial wilt etc.are considered to be an important limitation in pepper cultivation.In this paper,we investigated the changes of rhizosphere soil environment of grafted pepper and its relationship with the rot root and bacterial wilt resistant,using ?Weishi‘(WS)and ?Buyeding‘(BYD)as rootstocks and the cultivar pepper ?Xinfeng 2‘(XF)as scion.Meanwhile,we studied the disease resistant mechanism of grafted pepper by a manual inoculation method.The main results are as follows.1.Grafted pepper Xinfeng / Weishi(XF/WS)and Xinfeng / Buyeding(XF/BYD)slightly increased the conductivity(EC)in rhizosphere soil compared the control.XF/WS rhizosphere soil showed higher pH than the control,but no differences were observed in pH between XF/BYD and the control rhizosphere soil.XF/WS and XF/BYD significantly decreased the contents of nitrogen phosphorus and potassium,while increased fungus and actinomyces,the ratio of actinomyces,activities of soil phosphatase,invertase,urease catalase and peroxidase and hydrocarbon compounds in leach lipuor of rhizosphere soil,in comparison with the control.These data indicated that grafting can optimize the rhizosphere soil environment of pepper,and enhance the resistance of soil-borne diseases.The yields of XF/WS and XF/BYD were increased by 40.8% and 28.7% than the control respectively.2.Before inoculation of Fusarium solani(F.solani)and Ralstonia solanacearum(R.solanacearum),The roots of grafted pepper exhibited greater biomass and root activity than the control roots,no significant differences were observed in root absorption area and activity absorption area between grafted and non-grafted plants.After inoculation,less pathogenic F.solani and R.solanacearum invaded grafted pepper roots and consequently caused less serious injury to the root cell ultra-structure,compared with the control.Therefore,the roots of grafted pepper were less seriously injured,the cellular structure remained intact,and showed lower disease incidence and disease indexes and higher biomass,root activity and absorption area.This suggested that stronger roots of grafted pepper can prevent the F.solani and R.solanacearum invasion effectively.This is one of the important reasons of disease incidence improvement.3.After inoculation of F.solani and R.solanacearum,grafted pepper revealed lower hydrogen peroxide(H2O2),malondialdehyde(MDA)and electrolytic leakage(EL),while higher activities of catalase(CAT),ascorbate peroxidase(APX)and glutathione reductase(GR),compared with the control.Grafting also increased the contents of ascorbic acid(AsA),recuced glutathione(GSH)and ?-tocopheryl(?-TOC).This illustrated that grafting can alleviate the lipid peroxidation caused by F.solani and R.solanacearum invasion,through enhanced the antioxidant system activity in peppers.4.Grafted pepper root infected with F.solani and R.solanacearum exhibited higher contents of salicylic acid(SA),vanilline,lignin,polyamine,as well as the activities of phenylalanine ammonia-lyase(PAL),polyphenol oxidase,and POD compared with the control roots.These data suggested that grafting increased the secondary metabolism by enhanced the related enzymes activity of secondary metabolism,and consequently produced more phenolic acids and lignin,reinforced the mechanical barrier,strengthened the defense capacity and finally relieved the injury from pathogens to root cell.5.Rootstock,grafted and non-grafted pepper differ greatly in root exudate components.The root exudates of rootstocks and grafted pepper can inhibit the growth of F.solani and R.solanacearum,promote the seed germination and root growth of cucumber,and alleviate the negative effect of allelopathy on seed germination and root growth of tomato.This indicates that the changes of root exudate components in grafted plants is the one of the important mechanism of inhibition to growth and reproduction of pathogens,and alleviate the soil-borne disease.6.Through analysis to the root exudates components of rootstock and grafted pepper,we speculated that the inhibitory effect of root exudates in rootstocks and grafted peppers to pathogens may be related to diisooctyl phthalate and dibenzofuran.Data from functional analyses showed that 0.2 ml·L-1 diisooctyl phthalate and 0.1 g·L-1 dibenzofuran could decrease the disease incidence of pepper and the yields increased by 31.7% and 38.3% respectively compared with the control.