| Fusarium oxyporum f.Sp.Niveum(E.F.Smith)Snyder & Hansen(FON)is one of the main soil-bore diseases which threatened the production of watermelon(Citrullus lanatus(Thunb.)Matsum & Nakai).Continuous watermelon cropping can lead to serious problems,such as decreasing fruit quality,yield decline seriously,which has become the bottleneck probolem in watermelon production.In order to prevent the occurrence of diseases,application of large quantities of pesticides resulted in excessive pesticide residues,which seriously threatened people’s health and soil ecological environment.Exploring reasonable cultivate measure was regard as the more effective method to alleviate the incidence of watermelon wilt.Previous study showed that companion cropped with wheat could alleviate the incidence of watermelon wilt and improve the disease resistance of watermelon.However,the mechanism was not clear yet.Based on the screened materials with Fusarium wilt-suppressing characters in wheat root exudates,isolated and identified the antifugal substances in wheat root exudates by using extraction and column chromatography combined with TLC plate UPLC-Q-TOF-MS technology.Meanwhile determined the antifugal materials concentration in wheat rhizosphere soil and the half-life in the soil using HPLC chromatography.Tissue culture was used to study the effect of wheat root exudates on disease resistance of watermelon.A plant-soil feedback was conducted to examine the effects of changed microbs in the rhizosphere on disease resistance of watermelon.Likewise,explored the infulence of altered microbes and wheat root exudates on the expressions of defence-related genes,secondary metabolism substance content,and activities of pathogenesis-related in watermelon via q RT-PCR.In vitro,we anylazed the effect of root exudates on the pathogenicity of FON.Overall this study will facilitate plant disease control through a sustainable approach,which will reduce chemical application and benefit human health.It can also provide theoretical foundation and technical support for the application of the wheat companion cropping with watermelon.Main results of this study were as follows:(1)wheat root exudates from monoculture wheat and companion cropping wheat inhibited the mycelia growth of FON significantly(p<0.05),and the difference between the wheat monoculture and companion was not significant.The root exudates from monoculture wheat exhibit inhibitory effect on spore germinate of FON,but wheat root exudates from companion crooping wheat was not.The results indicated that wheat root exudates alleviated the incidence of watermelon wilt though inhibiting the growth of mycelia.Either watermelon root exudates in watermelon monoculture or watermelon root exudates in companion crooping with wheat has no significance difference compaison to the control.The watermelon root exudates from companion system inhibited the spore germination.The results suggested that comanion with wheat alted the composition of watermelon root exudates.(2)Extraction of wheat root exudates freeze-dried powder with different polar organic solvents,the material in ether phase exhibited inhibitory effect on the FON significantly;From the results of screen development solvent we obtained,we found that n-hexane: ethyl acetate =3:1 was the best.D0 point in the TLC exhibited inhibitory effect on the FON significantly,which isolated from TLC plate in the ether phase.15 compounds was isolated and identified using UPLC-Q-TOF-MS including 2 amides,1 sugar,2 phenolic acids and 10 alcohols.In vitro,the results indicated that the inhibitory effect was increased as the concentration of Phytosphingosine increasing,while the concentration reached 8μm,the effect reached its maximum.(3)The results of tissue culture experiment indicated that: the expression level of Cl PDF2.1 and Cl PDF2.4 genes were up-regulated significantly in wateremlon roots treatment with companion cropping with wheat,but the expression of PAL and CHI genes was no significance between the treatments.The content of lignin and total phonels was increased in the roots of companion with wheat treatments and the β-1,3-glucanase activities also increased after inoculated with FON 12 h.The results of exogenous addition of wheat root exudates experiment were similar to those of companion with wheat experiment.The expression of Cl PDF2.1,Cl PDF2.4,PAL and CHI genes were up-regulated in the treatment of addtion with wheat root exudates.Mean while,the content of lignin and total phenols increased significantly in watermelon roots of treated with root exudates before and after inoculation for 24 h,and the β-1,3-glucanase activities also increased significantly.Thses results suggested that wheat root exudates enhanced the resistance of watermelon though upregulation the expression of genes related to lignin and phytoalexin,increasing the content of total phenols and lignin and the activity of β-1,3-glucanase.(4)The results of plant-soil feedback experiment showed that the disease index and incidence of watermelon wilt were significantly reduced treatment of inoculated with companion with wheat soils in comparsion with the treatment of inoculated with watermelon monoculture soil.There was no significant difference between the treatment of inoculated with sterilized companion with wheat soil and the treatment of inoculated with sterilized watermelon monoculture soil.In the treatment of inoculated with companion wheat soil,the expression level of Cl PDF2.1 and Cl PDF2.4 genes was improved significantly,and also significantly improved the expression of CCOMT,CCR,POD and DAHPS genes related to lignin synthesis.Mean while,the content of lignin and total phenols in watermelon root was increased and the activity of β-1,3-glucanase in watermelon root was also increased.These results suggested that companionn cropping with wheat alleviates the incidence of watermelon wilt was related to the soil micoorganism.(5)The ability of FON to produce FA was inhibited as the concentration of exogenously addtion of wheat root exudate increased.And intracellular enzyme activity contaning pectinase,cellulase,β-glycosidase was reduced significantly after treated with wheat root exudates.With regards to extracellular enzymes,only protease activity was decreased after treated with wheat root exudates,which slows down the speed of protein decomposition.Addition of wheat root exudates induced decrease in the expression of those associated with cell wall biosynthesis CHI and six6,and up-regulated the expression of genes associated with autophagy.These results suggested that wheat root exudates could influence the pathogenicity in FON by inducing pathogen autophagy.In conclusion,companion cropping with wheat enhaced the resistance of watermelon to FON through wheat root exudates and soil microorganism.Companion cropped with wheat inhibited the growth and decreased the pathogenicity of FON through secreting inhibitory compounds,hence enhancing the defense ability of watermelon to FON.Companion cropping with wheat enhaceed the resistance of watermelon by secreting sencondary metabolites and changing the community of soil microorganism to regulate the expressions of genes related to secondary metabolites biosynthesis.The genes involved in lignin biosynthesis,phytolexin were all up-regulated in watermelon companioned cropping with wheat.Additionally,the content of lignin,total soluble phenolics,as well as defense enzyme(such as β-1,3gluance)activities all increased in watermelon companioned by wheat,thus hencing resistance of watermelon to FON and alleviating the incidence of watermelon wilt. |
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