| Astragalus root rot is one of the key factors that seriously restrict the sustainable development of Astragalus production.At present,among the prevention and control measures against Astragalus root rot,the cultivation and utilization of disease resistant varieties is the most economical and effective.This paper,regarding the interaction between Astragalus and root rot pathogens as the research system,mainly studied the production of cell wall degrading enzymes(CWDEs),the activation of plant defense enzyme systems and the dynamic change of metabolite types and their contents based on the~1H NMR,aiming to provide a new basis and research direction for the disease resistance breeding against Astragalus root rot and the discovery of new interaction mechanisms.(1)The activities of CWDEs produced by F.acuminatum,F.solani and F.oxysporum,the dominant pathogens in Shanxi province,were detected in vitro and in vivo by spectrophotometric methods in different periods.It was found that three Fusarium spp.can produce Polygalacturonase(PG),Pectin methyl-galacturonase(PMG),Carboxymethyl cellulose enzyme(Cx),β-Glucosidase(βG),Polygalacturonic acid traneliminase(PGTE)and Pectin methyltraneliminase(PMTE).Among them,the ability of F.acuminatum to produce PG,PMG,βG and PMTE was the strongest;the ability of F.solani to generate PGTE was significantly higher than that of other pathogens;and the abilities of F.solani and F.oxysporum to produce Cx were stronger than that of F.acuminatum.Based on the above results,the activities of PG,PMG,Cx andβG,the most important enzymes produced by the three pathogens,were detected in vivo.The results indicated that the ability of F.solani to produce PMG was stronger than that of other pathogens;F.acuminatum had a stronger ability to produce PG and Cx;the ability of F.oxysporum to produceβG was better than that of F.solani and F.acuminatum.It was concluded that the abilities of the three Fusarium spp.to produce CWDEs were different in vitro and in vivo,and their pathogenic mechanism were therefore different.(2)F.solani and F.acuminatum,which had strong pathogenicity,wide distribution and high frequency of separation in Shanxi province,were selected as the objects of further research.Astragalus roots were inoculated by soaking root method,and the activities of plant defense enzymes were determined by spectrophotometry methods.In the process of Astragalus roots being infected by F.solani,the activity of Phenylalanine amrnonia-lyase(PAL)decreased gradually with the increase of the disease index,and was significantly lower than that of the control.The activity of Peroxidase(PPO)in the inoculation group had no obvious changes at the early stage of infection compared with the control,and was significantly lower than the control in the later stage.Although the activity of Polyphenol oxidase(POD)was slightly higher than that of the control,there was no significant change in different stages.However,the activity of Superoxide dismutase(SOD)was increased significantly with the increase of the disease index,and was higher than that of the control.These results showed that the activities of PAL,PPO and POD were not activated,while significant increase of the SOD activity may predict the activation of active oxygen scavenging system.After the Astragalus roots were infected by F.acuminatum,the activities of PAL,POD,PPO and SOD first increased and then reduced with the severity of disease,and the activities of defense enzymes were obviously higher than those of control.Among them,SOD activity reached its peak at 7 d;POD,at 14 d;PAL and PPO,at 21 d.The results showed that the defense enzyme activities were activated,but the peak of activities appeared at different times in the process of Astragalus roots’infection by F.acuminatum.It is conjectured that the different mechanisms of plant disease resistance were induced by the different pathogenic mechanisms of the two pathogens.(3)Finally,F.solani,the most important pathogen,was selected as the research object.Astragalus roots were inoculated by pouring root method,taking uninoculated Astragalus as control and collecting samples at different time points.The dynamic changes of the metabolite types and contents were detected by~1H NMR technology.Thirteen differential metabolites were found by combining PCA with OPLS-DA in multivariate statistical analysis.Among them,amino acids included valine,arginine,threonine,GABA,alanine,glutamine,aspartic acid and phenylalanine;organic acids,citric acid,taurine and malic acid;and the sugars,fructose and sucrose.Correlation analysis between the compound contents and incidence of Astragalus found that there were eight metabolites closely related to root rot disease.A verification test of the disease related metabolites was then carried out,and it is confirmed that the resistance indicators were aspartic acid,phenylalanine,sucrose and fructose;and the disease indicator was glutamine. |
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