| A root disease was found in the Astragalus plantation of Tuoming Agricultural Development Co.,LTD.,Ningxia.The incidence was mainly in the root crown.The skin was brown to black rot and cracked,it was named Astragalus crown rot.Preliminary investigation showed that the incidence of annual seedlings was about 15%,and the incidence of severe plots after transplantation was up to 40%,which caused great loss to the yield and quality of astragalus.In this paper,in view of the occurrence of Astragalus crown rot,the identification of pathogenic bacteria,quantitative Real-time PCR detection of main pathogenic bacteria,screening of indoor disease control agents and field control tests were carried out.The main research results are as follows:1.Pathogen identification of Astragalus crown rot.Astragalus strains with typical symptoms were selected,and the pure culture was obtained by tissue separation and single sporulation separation.The pathogens determined by Koch’s rule were identified by morphological and molecular biological methods.The results show that:Fifty-two isolates were isolated and sequenced using rDNA-ITS,TEF1α,β-TUB gene sequences for multigene combination phylogenetic analysis.The pathogens causing Astragalus crown rot were identified as Fusarium equiseti,Fusarium acuminatum and Fusarium oxysporum with the isolation frequencies of 57.7%,25%and 17.3%,respectively.F.equiseti was the dominant pathogen of Astragalus crown rot.2.Establishment of fluorescence quantitative PCR assay system for Fusarium equiseti.A quantitative Real-time PCR system for Fusarium equiseti was established.The minimum detection amount of the system was 1.0×10-3ng·μL-1,and its sensitivity was 100 times that of conventional PCR.The system can be used for the quantitative detection of Fusarium equiseti in soil and plants in the field.The quantitative study of Fusarium equiseti in soil under different rotation modes showed that the content of Fusarium equiseti in soil under different rotation modes in Yanchi base was higher than that in Guyuan seedling cultivation base on the whole,and the content of Fusarium equiseti was the lowest in 0-10cm overlying soil layer,and the highest in 10-30cm astragalus planting layer.In production,with a three-year crop rotation cycle,it is recommended to promote the planting of astragalus in the first year,the rotation of other crops in the next year,and the choice of fallow in the third year.This will keep the content of Fusarium equiseti in the soil low,so as to reduce the occurrence of disease.3.Laboratory toxicity determination of different agents to pathogens of Astragalus crown rot.The indoor virulence of 13 fungicides against the pathogens of Astragalus crown rot,Fusarium equiseti,Fusarium acuminatum and Fusarium oxysporum was determined by growth rate method.The results showed that the cyanomycobin and pentazole had the best inhibition effect on the three pathogens,with EC50 values of 0.048 mg/L,0.7764 mg/L,1.8113 mg/L and 0.3175 mg/L,0.8221 mg/L,0.8829 mg/L,respectively.The EC50 values were 16.9005 mg/L,15.4704 mg/L,75.2142 mg/L and 69.2787 mg/L,16.2218 mg/L,60.3949 mg/L,respectively.Trichoderma harzia had the best inhibition effect,and the EC50 values of the three pathogens were 2.5305 mg/L,4.5930 mg/L and 11.5904 mg/L,respectively.Mesocin of agricultural antibiotics showed good virulence to the three pathogens,with EC 50 values of 189.4524 mg/L,69.7108 mg/L and 171.8304 mg/L,respectively.4.Field test of different agents against Astragalus crown rot.According to the results of laboratory toxicity test,eight kinds of drugs were selected to soak the root of annual seedlings of Astragalus membranaceus and plant.After harvest,disease occurrence was investigated and growth index of Astragalus membranaceus was measured.The results showed that pentazole and cyanoconoxystrobin had the lowest incidence and disease index,and the highest average yield.Through correlation analysis,it was found that there was a significant negative correlation between the disease index and the yield,and the two agents had the best preventive efficacy,with 74.01%and 71.66%respectively,which were 37.4%and 35.05%higher than the prevention efficacy of the production drug Jia Oxamyl,and the yield was very different from that of the production drug Fine Methyl Oxa,which was very different.The control efficiency of mesocin was 61.84%and 50.79%,respectively,under the treatment of 500x and 1000x.It was 25.23%and 14.18%higher than methylidene,respectively.The control effect of biological agent Bacillus subtilis was 45.67%,which was 9.06%higher than that of methylidene·oxametrin,so pentazole and cyanomystrobin were recommended for the field control of astragalus crown rot. |
PDF Full Text Request