| In recent years,the cultivation of muskmelon（Cucumis melo L.）has gradually become a facility,and the production has become large-scale,which has aggravated the occurrence of continuous cropping obstacles of muskmelon.Grafting muskmelon with disease-resistant rootstocks can improve the tolerance of plants in adverse environments and overcome the obstacles of continuous cropping,but its mechanism remains to be studied.In this paper,the effects of disease-resistant pumpkin rootstock grafting on the growth and development of melon plants and the disease resistance to melon Fusarium wilt were studied;the allelopathic effects of root exudates of each treatment were analyzed,on this basis,the allelopathy of key active substances were explored by simulation;the effect of grafting on the rhizosphere microbial community of melon plants was clarified.The purpose of this study is to provide theoretical support and reference value for further revealing the physiological mechanism of grafting and root changing to improve the growth vigor and resistance to Fusarium wilt of melon,and the mechanism of grafting to alleviate the continuous cropping obstacle of melon.The results of the study are as follows:1.Grafting promoted the growth and development of melon plants and significantly reduced the incidence of melon Fusarium wiltTwo disease-resistant pumpkin rootstocks were selected to graft muskmelon to study the effect of grafting on the growth vigor of muskmelon plants,and to identify the resistance of muskmelon plants to Fusarium wilt under artificial inoculation with Fusarium oxysporum and simulated muskmelon continuous crop soil natural cultivation conditions.The results showed that grafting significantly increased the plant height,stem diameter,number of leaves,and the content of chlorophyll and lignin in leaves during the growing period of melon.Both stock and ear grafting combinations Shengzhen No.1/Chaotianmibao（SJ）and J-type cantaloupe rootstock/Chaotianmibao（JJ）showed high resistance（HR）,while melon self-rooted seedlings（TZ）showed susceptible（HS）,with an incidence rate of more than 80%.Grafting of disease-resistant pumpkin rootstocks significantly improved the resistance of melon plants to Fusarium wilt.2.Allelopathic effects of root exudates from self-root and grafted plantsThe root exudates of self-rooted and grafted plants were used to treat Fusarium oxysporum and melon.The results showed that the root exudates of melon self-rooted seedlings（TZ）promoted the mycelial growth of Fusarium oxysporum,while the root exudates of root stock grafting combinations（SJ,JJ）and pumpkin rootstock seedlings（SZ,JZ）inhibited their growth,and the antibacterial effect of root exudates from JZ and JJ was significantly better than that of SZ and SJ.The root exudates of SZ and JZ had the best promotion effect on melon seed germination,radicle length and melon plant growth vigor,followed by SJ and JJ,while TZ showed the inhibitory effect.There were active substances in the root exudates of disease-resistant pumpkin rootstocks and grafted muskmelon plants that can inhibit the mycelial growth of Fusarium oxysporum,promote plant growth and improve the disease resistance of muskmelon plants.3.The composition and content changes of the main allelopathic substances in the root exudates of the grafted muskmelonThe composition and content of root exudates of self-root and grafted plants were determined by HPLC.The results showed that there were 7 kinds of phenolic acids（ferulic acid,gentisic acid,cinnamic acid,vanillic acid,protogermic acid,phthalic acid,p-hydroxybenzoic acid）and 3 kinds of organic acids（oxalic acid,malic acid,fumaric acid）in root exudates,of which oxalic acid only existed in root exudates of stock and ear grafting combinations（SJ,JJ）,and the relative content of gentisic acid was the highest in root exudates of each treatment.Grafting significantly increased the total content of phenolic and organic acids in root exudates of melon.4.The allelopathic effects of simulated root exudates on Fusarium oxysporum,seed germination and plant growthThe allelopathic effects of five active substances in root exudates of ferulic acid,gentisic acid,malic acid,fumaric acid and oxalic acid were studied by exogenous addition method.The results showed that when the concentration of fumaric acid was 0.05 mmol·l-1,the antibacterial effect was the most significant;malic acid inhibited the growth of mycelium at all concentrations;ferulic acid has the strongest inhibitory effect on melon seed germination and plant growth;when the concentration of oxalic acid was 0.5-2 mmol·l-1,and the concentration of malic acid and fumaric acid was 0.05-1 mmol·l-1,seed germination could be promoted,all three organic acids could increase the biomass of melon seedlings,and malic acid and fumaric acid had the most significant promoting effects on radicle length and plant growth,respectively.Grafting changed the relative content of phenolic acid and organic acid in root exudates of melon plants,the content of organic acid was significantly increased,the growth of pathogens was inhibited,and the plant growth vigor was enhanced.5.Grafting could change the rhizosphere soil microbial community structure and diversity of melon plants under continuous cropping conditionsIllumina Mi Seq high-throughput sequencing technology was used to analyze the effect of grafting on the microbial community structure of the rhizosphere soil of melon plants.The results showed that grafting significantly increased the diversity and abundance of bacteria and fungi in the rhizosphere soil of melon plants under continuous cropping conditions.At the fungal genus level,Fusarium was the dominant genus in the rhizosphere soil of self-rooted and grafted plants.Under continuous cropping conditions,its relative abundance in the rhizosphere soil of self-rooted melon plants increased significantly,while its relative abundance in the rhizosphere soil of grafted melon plants decreased significantly.Grafting changed the community structure of the melon plant soil microorganisms,the beneficial bacteria in the soil proliferated,and the number of Fusarium spp.decreased,which could reduce the incidence of melon Fusarium wilt under continuous cropping conditions. |
