Study On The Mechanism And Prevention And Control System Of Continuous Cropping Obstacles Of American Ginseng

American ginseng(Panax quiquefolium L.)is a perennial medicinal plant belonging to the Panax of Acanthaceae.It has high medicinal and economic value and is widely cultivated in Jilin,Shandong and Shaanxi provinces.American ginseng is a long-term soil-welling plant with a growth cycle of 4 to 5 years.Its unique cultivation characteristics always lead to serious continuous cropping obstacles in the planting process,resulting in a sharp decline in the yield and serious damage to its quality,which severely hindering the healthy development of American ginseng industry.From 2020 to 2023,this research has carried out a large number of studies on the fungi carried by seeds and the etiology of verticillium wilt of American ginseng,in order to improve and enrich the formation mechanism of continuous cropping obstacles.On this basis,we constructed a control technology system under "2+2" planting pattern(The 4-5-year growth cycle of American ginseng was artificially divided into two years of factory box bagging three-dimensional planting and then two years of field planting,which was called "2+2" planting pattern),aiming at exploring and overcoming continuous cropping obstacles and reducing technical barriers.It laid the theoretical foundation and technical support for the factory,three-dimensional and modern planting of American ginseng.The main findings are as follows:1.The fungi carried in seeds of American ginseng from major producing areas in China were determined by traditional isolation culture method and high throughput sequencing method.The results showed that the fungi carrying rates of seeds from Wendeng and Rongcheng of Shandong Province,Fusong of Jilin and Liuba of Shaanxi Province were 45.7%,75.2%,93.8% and 100%,respectively.Sixty-seven fungi belonging to 28 genera were isolated from the tested seeds and 11 pathogens were identified.Fusarium spp.,the principal pathogen causing root rot and fusariumwilt of American ginseng were detected in all the seeds,and the relative abundance of Fusarium spp.in seed kernel was higher than that in shell.The inhibitory rates of the four tested fungicides(tebuconazole,azoxystrobin,fludioxonil and phenamacril)on the fungi carried by American ginseng seeds were 71.83%,46.67%,46.08% and 11.11%,respectively,while the conventional seed coating agent fludioxonil had a low inhibitory rate on the fungi carried by American ginseng seeds.These results indicated that the variety and quantity of pathogenic fungi carried by American ginseng seeds from major producing areas in China may be one of the reasons leading to the continuous cropping obstacles of American ginseng.In addition,the fungi carried by seeds have developed resistance to traditional agents.2.Verticillium isaacii was reported for the first time to be the pathogen causing verticillium wilt of American ginseng,and verticillium wilt may be one of the soil-borne diseases causing continuous cropping obstacles of American ginseng.The biological characteristics showed that V.isaacii could grow and sporulate on different nutrient types of medium.There is no obvious preference in carbon and nitrogen metabolism,but there are differences in the utilization of different carbon and nitrogen sources.The effects of p H on mycelial growth and sporulation were different,alkaline environment was conducive to colony growth,but acidic environment was more favorable for producing spores.Temperature has a great influence on mycelium growth,25℃is the optimal temperature for mycelium growth,but both high and low temperature are not suitable to growth.The pathogen had a wide host range,and could infect eggplant,melon,sunflower,cotton,cucumber,tobacco and beet artificially,and showed obvious symptoms.The results of pathogen biology showed that V.isaacii has a wide adaptability of p H value and temperature,and can grow and produce spores under favorable environmental conditions suitable for host growth.It can also use different types of nutrients in the soil for mass reproduction,and cause the occurrence and spread of diseases under appropriate conditions.3.On the basis of the previous research results on the formation mechanism of continuous cropping obstacles of American ginseng,we proposed the idea of reducing the continuous cropping obstacles by breaking the traditional planting pattern of American ginseng for 4 to 5 years,and constructed the prevention and control technology system of continuous cropping obstacles based on the "2+2" planting pattern.The results of cultivation experiment showed that the "2+2" planting pattern not only could significantly improve the emergence rate,survival rate and transplanting survival rate,but also could increase the growth potential and biomass of American ginseng seedlings.The seedling emergence rate of "2+2" box treatment group was 66.47%,17.22 times of that of field control group,and significantly higher than that of other groups.The seedling survival rate was 76.43% in the box treatment group,which was 6.4 times that of the box control group and 1.9 times that of the field soil remediation group,all plants died in field control group.The transplanting survival rate of the box treatment group was 92%,which was significantly higher than that of the other groups.The box control group,field soil remediation group and field control group all died after transplanting until the statistical date.Comparative analysis of growth trait indexes showed that the average plant height and leaf width of two-year old American ginseng in box treatment group were 10.37 cm and 4.85 cm,respectively,significantly higher than that in box control group and field soil remediation group.The results indicated that the "2+2" planting pattern could enhance the growth potential and improve the weak state of plant growth potential caused by continuous cropping obstacles,also could promote the normal growth and development of plants.The statistical comparison of biomass indexes showed that the average fresh weight and dry weight of root in box treatment group were 5.75 g/ root and 2.35 g/ root,which were significantly higher than those in box control group and field soil remediation group.The results suggested that the "2+2" planting pattern could promote the root growth and increase the yield of root,thereby,could overcome the phenomenon of yield reduction or destruction caused by continuous cropping obstacles.The above results showed that the "2+2" cropping system significantly reduced the impact of continuous cropping obstacles,which has important practical significance for the development of American ginseng industry.