Mechanism Analysis Of Inoculation With Mortierella Alpina On Defense Against Root Rot Of Cultivated Ginseng

Ginseng is a precious traditional Chinese medicine with multiple functions,such as enhancing organ functioning,inhibiting inflammation,preventing tumor and antiviral.As the first country to develop ginseng cultivation in the world,the cultivated area and yield of ginseng in China now ranks first.Therefore,ginseng’s role and economic status cannot be ignored.Because of the destruction of forest vegetation system and hazards forest ecological security,planted ginseng by deforestation has been strictly prohibited.Planting ginseng in farmland has been an irresistible trend.Many factors,such as serious soil-borne diseases,few beneficial microorganisms and nutrient imbalance etc.,restrict the further development of ginseng production.It is an urgent scientific problem to be solved that how to regulate soil microecosystem,promote the positive succession of microbial community and effectively control soil-borne diseases.In this study,the physicochemical and microbiological characteristics of different cultivated soil of ginseng were analyzed.And the distribution of Mortierella in soil and its correlation with soil health were clarified.Furthermore,to clarify the control potential of Mortierella against soil-borne diseases,the interaction between Mortierella,Fusarium oxysporum and ginseng was analyzed by plate culture and pot experiments.The results obtained are as follows:（1）By analyzing the soil nutrients in forestland,farmland and 4-year ginseng-cultivated soil,we found that the contents of available nitrogen（NO₃^--N and NH₄⁺-N）,available phosphorus,total nitrogen,total phosphorus and organic matter were significantly different in different types of soil.High-throughput sequencing showed that Alpha diversity index indicated that the richness and diversity of bacteria and fungi in forest soil were significantly higher than that in 4-year ginseng-cultivated soil.There was high relative abundance of Mortierella in all different types of soil.And the relative abundance of Mortierella in forest soil was significantly higher than that in farmland and 4-year ginseng-cultivated soil.It is suggested that the abundance of Mortierella may be a biotic indicators of soil health.（2）An Mortierella strain was isolated from the rhizosphere of ginseng and its interaction with soil microorganisms and growth promoting potential were analyzed.The results showed that the mycelial growth of M.alpina was inhibited by probiotics such as Bacillus,Streptomyces,Brevibacterium,Trichoderma,Penicillium and potential pathogens such as Cladosporium and Aspergillus.However,there was no obvious interaction with F.oxysporum,the pathogen of ginseng root rot.M.alpina had a high indoleacetic acid production capacity,and the maximum yield was 141.37 mg/L at 4 days.And the protease activity was 5.5 U/mL at 5 days.However,M.alpina did not have the ability to produce siderophores,dissolubilize phosphorus and the activities of amylase,cellulase,pectinase and xylanase.（3）To investigate the effects of inoculation with M.alpina on the disease resistance of ginseng,pot experiment was conducted by inoculation with M.alpina（MA）,F.oxysporum（FO）and both of them（MA＿FO）.The results showed that inoculation of M.alpina in ginseng rhizosphere could significantly alleviate the symptoms of root rot.Co-inoculation of M.alpina and F.oxysporum could reduce the relative abundance of potential pathogens and increase the relative abundance of beneficial microorganisms in ginseng plants,and help the root of ginseng to build a more stable microbial network to promote the growth of ginseng plants.（4）Results of the physicochemical and microbial communities in the rhizosphere soil of ginseng inoculated with M.alpina and/or F.oxysporum showed that inoculation of M.alpina could significantly increase the contents of ammonium nitrogen,available phosphorus and available potassium and the activities of urease,sucrase and acid phosphatase.The results based on db-RDA analysis showed that ammonium nitrogen and available phosphorus content were the most important factors affecting rhizosphere bacterial and fungal communities,respectively.Linear regression analysis showed that M.alpina could resist F.oxysporum invasion by increasing the activity of soil sucrase.Combined with the analysis of soil microbial composition and the differences between groups,it was found that inoculation of M.alpina could significantly reduce the relative abundance of F.oxysporum in soil,and contribute to the positive succession of soil physicochemical and microbial communities.