Molecular Identification And Screening On Fungicides Of Cylindrocarpon (Ilyonectria) Species Associated With Ginseng Root Rust Rot In Northeastern China

Panax ginseng C.A.May is a perennial medicinal plant of the Araliaceae Panax,which has a very high medicinal and economic value.The Ginseng root rust rot(GRRR)caused by Cylindrocarpon destructans(Zinns.Scholten)is one of the most common and serious soil-borne diseases in ginseng cultivation,which seriously restricts the development of ginseng industry.In this study,forty-five strains were isolated from samples collecting,which were identified by combining morphological characters and ITS sequence analysis.The biological characteristics of different species were compared by mycelial growth rate method.The pathogenic mechanism was revealed by comparing the activity of CWDEs of different species fungi in vivo and in vitro.Different fungicides were selected to determine the virulence of Cylindrocarpon destructans indoors and in pots.The results were as follows.In order to clarify the classification of 45 strains in the main producing areas of northeastern China,morphological characters and ITS sequence analysis were used integrately in this study.The results showed that there were three species causing GRRR in Northeast China,among which Cylindrocarpon destructans was the most prevalent species representing 62.22%(28 of 45)of the isolates,mainly distributed in Liaoning Province and Jilin Province;followed by Ilyonectria robusta,representing 31.11%(14 of 45)of the isolates,which was widely distributed in Northeast China;Cylindrocarpon destructans var.destructans representing 6.67%(3 of 45)of the isolates and only appeared in Liaoning Province.Pathogenicity tests results showed that the pathogenicity of C.destructans var.destructans was strong,followed by C.destructans and I.robusta was relatively weak.In order to clarify the differences in the biological characteristics of the three kind of pathogens,the effects of different environment conditions on mycelial growth and sporulation of the three representative strains were studied.The results showed that the optimum carbon source for mycelial growth and sporulation of strain R7 was fructose,peptone was the optimum nitrogen source for mycelial growth and KNO3 was the optimum nitrogen source for sporulation;the optimum p H for mycelial growth was 6,and the optimum p H for sporulation was 7;the optimum temperature for mycelial growth and sporulation was 20℃;PDA medium was the optimum medium for mycelial growth and sporulation;and sporulation was suitable in dark condition.The optimum carbon source for mycelial growth and sporulation of strain X25-5 was lactose and fructose;the optimum nitrogen source for mycelial growth was peptone and the optimum nitrogen source for sporulation was NH4Cl;the optimum p H for mycelial growth and sporulation was 6;the optimum temperature for mycelial growth and sporulation was 20℃;the optimum medium for mycelial growth and sporulation was PDA;and dark condition was suitable for sporulation.The optimum carbon source for mycelial growth and sporulation of strain YL026 was lactose and glucose;the optimum nitrogen source for mycelial growth and sporulation was peptone;the optimum p H for mycelial growth and sporulation was 8;the optimum temperature for mycelial growth and sporulation was 25℃;the optimum medium for mycelial growth was Czapek;the optimum medium for sporulation was MEA;dark condition was favorable for pathogenic bacteria growth and sporulation.In order to identify the main pathogenic factors of three species,the CWDEs of Cylindrocarpon destructans var.destructans strain R7,Cylindrocarpon destructans strain X25-5 and Ilyonectria robusta strain YL026 were systematically studied in vitro and in vivo.The results showed that PG,PMG,Cx and β-glucosidase could be produced by three kinds of fungi in vitro and in vivo.In vitro,mixed culture medium had the best induction effect on PMG and PG,while cellulose culture medium had the best induction effect on Cx and β-glucosidase.Strain R7 had the strongest ability to produce enzymes in different culture media,which was consistent with its pathogenicity.In vivo,Cx enzyme was the first one that played an important role after strain R7 infected ginseng roots.With the increase of infection time,cellulase and pectinase reached their peak value on the 12 th day,and there was obvious synergistic effect in the process of ginseng infection.The Cx and β-glucosidase played an important role in the infection of Ginseng by strain X25-5.When strain YL026 infected ginseng,PG activity played a major role in the interaction between pathogen and ginseng.Three fungicides with good control effect were screened out,namely 10%Difenoconazole WG,400 g/L Fluorosilazole SC and 100 g/L Cyanofrozole EC.Ten fungicides were screened through indoor virulence test and pot experiment.Indoor virulence test showed that 10% Difenoconazole WG,400 g/L Fluorosilazole SC and 100g/L Cyanofrost zole EC had better effect on ginseng rust rot fungus,followed by 50%Pyloridine WG and 50% Tacrolim WG.The results of pot experiment showed that 10%Difenoconazole WG and 400 g/L Fluorosilazole SC had the best control effect on ginseng rust rot.The emergence rate was 82.77% and 80.73% respectively.The control effect could reach 63.88% and 59.25% respectively,followed by 100 g/L Cyanofrost EC.The emergence rate was 75.67% and the control effect reached 54.61%.The results of pot experiment were consistent with those of indoor virulence test.