| The Zherong County,administered by the Ningde City,is facing the problems of soil degradation,increasing severity of the leaf spot disease,and a serious decline in the quality and yield of Pseudostellaria heterophylla owing to long-term monoculture of the plant.To reduce the local incidence of leaf spot disease,this study combined traditional morphological identification methods and molecular methods to isolate and identify the pathogenic bacteria of Pseudostellaria heterophylla.The identified bacteria were used as the targets to isolate,screen,and identify potential antimicrobial actinomycetes.Finally,the selected actinomycetes were applied in the field experiments.This study also investigated the effect of spraying an actinomycetes fermentation solution on the soil environment and the prince ginseng root system,including soil microorganisms,soil enzyme activity,and soil physicochemical properties,to elucidate the effect of actinomycetes on the soil environment and in the field.The results of this study were as follows:(1)Five strains were initially isolated from the leaves of Pseudostellaria heterophylla affected with leaf spot diseased collected from Fengyang located in Zherong County,Ningde City,Fujian Province.Using Koch’s law,fungus A was found to be the source of the local leaf spot disease.Morphological observation indicated that A strain did not produce conidia when cultured on the potato dextrose agar.The conidiophores were globular with orifices and contained a large number of conidia.Microscopic observation of A strain indicated that spore morphology and other characteristics were similar to those of the previously isolated and identified Ascomycota.The sequence of A strain was amplified using ITS-PCR and was found to have 97% similarity to that of KP899427 present in the NCBI database.Finally,A strain was identified as belonging to Ascomycota.(2)A total of 213 strains of actinomycetes were isolated and screened from the soil of the Pseudostellaria heterophylla root system from Zherong county in Ningde City.Using fungus A as the target,48 strains of actinomycetes with antimicrobial effects were identified.Based on the inhibition activity,B-26,A-26,and N-1 strains were finally selected for field experiments on Pseudostellaria heterophylla.Using a combination of morphological evidence,physiological and biochemical activity assays,and molecular methods,B-26,A-26,and N-1 were identified as Streptomyces albulus,S.xanthocidicus,and S.tsukiyonensis,respectively.(3)Spraying the actinomycete solution increased the population of most soil microorganisms and decreased the number of soil fungi.Results of 16 Sr DNA high-throughput sequencing showed that the proportion of soil actinomycetes increased after spraying the actinomycete solution,suggesting that the strain was well adapted.However,the diversity of soil bacteria decreased upon spraying the solution,and the number of bacterial populations increased in the plate counting method,suggesting that the actinomycetes solution not only suppressed soil fungi but also other microbial species in the soil.The A-26 and N-1 actinomycetes were able to suppress the soil fungi well compared with the control and B-26 actinomycetes.Spraying the actinomycete solution increased the activity of most of the soil enzymes but had no significant effect on peroxidase activity and reduced soil FDA hydrolase activity.Spraying the three actinomycete solutions was observed to enhance nutrient content of the soil but had no significant effect on p H.Spraying the B-26 solution did not increase the yield and increased disease incidence in the field experiment,whereas spraying with A-26 and N-1 solutions,increased the yield and decreased disease incidence.In conclusion,as compared with B-26,actinomycetes A-26 and N-1 could improve soil fertility,enhance resistance to leaf spot disease,and increase yield by suppressing the soil fungal population and increasing the populations of most functional microbes. |
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