Study On The Interaction Of Fusarium And Trichoderma With Panax Ginseng And Their Effects On Its Growth And Development

Objective:Continuous cropping obstacles seriously restricted the sustainable development of ginseng industry in China.More and more evidences showed that the imbalance of microbial community structure in Panax ginseng cultivation soil was the core factor caused continuous cropping obstacles.The results of previous studies showed that the increasing cultivation years of ginseng resulted in a large number of pathogenic fungus such as Fusarium sp.in ginseng field,which led to the increasingly serious mycosis and bacterialization of the planted ginseng soil.In this study,the interaction of“ginseng---rhizosphere microorganisms”as the starting point and took pathogenic Fusarium and beneficial Trichoderma in rhizosphere soil of ginseng as the research objects.On the one hand,the interaction between pathogenic Fusarium,Trichoderma and ginseng root exudates was explored.On the other hand,the effects of exogenous microorganisms（pathogenic Fusarium and Trichoderma）on the microbial diversity and growth and development of ginseng were investigated.This study aimed to clarify the key factors inducing the proliferation of pathogenic Fusarium species in the soil of Panax ginseng,to help understood and explained the mechanism of continuous cropping obstacle of Panax ginseng from the microorganism level,and reveal the role of ginseng rhizosphere microenvironment in the quality formation of ginseng medicinal materials.method:In this study,dilution-plate method and tissue separation method were used to isolate pathogenic Fusarium and Trichoderma from ginseng soil.And meanwhile the morphological characteristics and rDNA-ITS sequences were applied to determine the specific types.Eventually,the chemotactic responses of Fusarium and Trichoderma to root exudates of ginseng were studied by improved capillary method.The effects of adding exogenous microorganisms（pathogenic Fusarium and Trichoderma）on the microbial richness and diversity in the soil of ginseng were analyzed and compared by using the high-throughput sequencing method of Illumina hiseq 2500.The effects of adding exogenous microorganisms（pathogenic Fusarium and Trichoderma）on the growth and development of ginseng and the contents of ginsenoside Rg1,Re and Rb1 were observed by pot experiment and HPLC.Results:1.27 strains of fungi were isolated from ginseng diseased plants and rhizosphere soil,and identified by morphology and ITS-rDNA technology.Two Fusarium and two Trichoderma strains were isolated and identified from ginseng soil,among which NRS-5 was Trichoderma gamsii,NRS-7 was Trichoderma viride,NRS-9 was Fusarium oxysporum,NRS-23 was Fusarium verticillioides.2.It showed that two Fusarium were showed significant chemotaxis to exogenous ginsenosides and benzoic acid（P<0.05）,as while two Trichoderma were showed no significant chemotaxis at medium and low concentrations（P>0.05）.Two Fusarium had significant positive chemotaxis to the high concentration of water extract and ethanol extract of ginseng rhizosphere soil with different cultivation years（P<0.05）.With the increase of cultivated years,chemotaxis of extracts from ginseng rhizosphere soil caused by the lower the effective concentration(2 mg·L^-1).Two Trichoderma had no significant chemotaxis to water extract from different cultivation years of ginseng rhizosphere soil（P>0.05）,but significant positive chemotaxis to the high concentration of alcohol extract,following with the increase of cultivation years the chemotactic effect enhanced.3.Effects of exogenous microorganisms on microbial diversity in ginseng rhizosphere soil showed that 1256 OTUs were obtained by Illumina HiSeq 2500 high-throughput sequencing using OTUs clustering at 97.0%similarity level.The sequencing data of this study was reasonable and could reflect the types and structures of fungal communities in the samples.Fifteen dominant fungal communities were screened from rhizosphere soil of ginseng,of which the relative abundance of more than 1%were Mortierella,Fusarium,Humicola and Simplicillium.The diversity and richness of fungi in rhizosphere soil of ginseng add with Fusarium oxysporum（LD,LG）and Trichoderma viride（MD,MG）groups were lower than those in control（QS）group,and the fungal community structure of LD,LG group was different from QS group.There were significant differences in the microflora of LD,LG group and QS group at the genus level（P<0.05）.There was no significant difference in the microflora at the genus level between the MG,MD and QS groups（P>0.05）.4.There were no significant difference in leaf number,root length,root diameter and root fresh weight of ginseng plant between F.oxysporum,T.viride groups and QS group（P>0.05）.Panax ginseng plant height in high concentration T.viride（MG）group was significantly higher than that in QS group（P<0.05）,there was no significant difference in ginseng plant height between F.oxysporum group and QS group（P>0.05）.The addition of F.oxysporum could inhibit the synthesis of ginsenoside Rg1,while T.viride significantly promoted the synthesis of ginsenoside Rg1.The addition of F.oxysporum at low and medium concentrations increased the contents of Re and Rb1,while the addition of F.oxysporum at high concentrations decreased the contents of Re and Rb1.The addition of high concentration T.viride could significantly promote the synthesis of Re and Rb1.Conclusion:Water-soluble substances such as ginsenosides and phenolic acids secreted by ginseng roots can be used as chemical inducers of pathogenic Fusarium,but the effect on Trichoderma induced proliferation is not significant.This finding is conducive to the further exploration of the interaction between ginseng,pathogenic Fusarium and Trichoderma under natural conditions,and has important theoretical significance to elucidate the biological mechanism causing continuous cropping disorders of ginseng.Exogenous addition of F.oxysporum and T.viride will decrease the fungal diversity and richness of rhizosphere soil of ginseng,thus causing the imbalance of soil microecology.The addition of high concentration T.viride can significantly promote the growth of ginseng plants and the synthesis of ginsenoside Rg1,Re and Rb1.The inoculation of F.oxysporum has no significant effect on the growth of ginseng plants,but promote the production of ginsenoside Re and Rb1 to a certain extent.