| American ginseng(Panax quiquefolium L.)is a perennial herbaceous plant of the Araliaceae family and a well-known tonic traditional Chinese medicines.Its medicinal part is dry root,which generally takes 4-5 years from seeding to harvest of fresh root.In China,there are three main producing areas:Fusong in Jilin,Wendeng in Shandong and Liuba in Shaanxi.Continuous cropping obstacles had become a bottleneck factor in the development of American ginseng industry,which severely restrict the sustainable development of the American ginseng industry and cast off poverty to get rich.From 2017 to 2020,focusing on the continuous cropping obstacles of American ginseng,we carried out continuous cropping obstacle evaluation,main soil-borne diseases etiology research,and soil remediation of continuous cropping fields.The following main results were obtained:1.Based on the soil-borne disease,incidence,soil physical and chemical properties and property of continuous cropping,the field of continuous planting of main American ginseng planting area in Liuba county was investigated in two consecutive years by field investigation,laboratory isolation,identification and statistical analysis.The results showed that the disease incidence rate of American ginseng continuous cropping land was more than 60%,which was more than three times that of newly cultivated land.Soil-borne diseases such as American ginseng root rot(Fusarium.spp.),American ginseng rust rot(Cylindrocarpon spp.),American ginseng sheath blight(R.solani),American ginseng damping-off(Pythiaceae)and American ginseng sclerotia(S.sclerotiorum)was common in continuous cropping field.The p H of continuous cropping field dropped significantly.The average yield of 4-year-old American ginseng is 3000 kg/hm~2,which is less than 50%of the output of new cultivated land,and even some continuous cropping plantations have no harvest.It was concluded that the obstacle of continuous cropping of American ginseng might be related to the change of physical and chemical properties and the imbalance of soil microbial flora of the continuous cropping land in Liuba.2.Based on isolation re-inoculation,morphological characteristics observation,and homology comparison of ITS sequence,it was determined that the pathogen of the main soil-borne diseases root rot in American ginseng continuous cropping fields were F.solani,F.oxysporum and F.redolens.And F.redolens is the first reported species on American ginseng.The results of biological characteristics research of F.redolens showed that the suitable growth temperature range is 10-40℃,and the optimum temperature is 25℃.F.redolens can make full use of carbon and nitrogen sources with little effect,but have significantly affect on the spore production,and which had significant differences in the utilization of organic nitrogen and inorganic nitrogen.And that colony diameter and spore production were significantly different under different p H conditions,and the growth condition was the best when the p H was 6,indicating that the strain was suitable for growth in a slightly acidic rhizosphere environment.3.Investigating the seedlings condition of American ginseng under different soil remediation treatments for 2 consecutive years.The results show that the number of emergence of American ginseng has been significantly improved.The number seedlings of 1-year-old American ginseng increased by 2.71 times and that 2-year-old American ginseng increased by16.66 times with MA14,which has a significant effect on reducing the obstacles to continuous cropping of American ginseng.At the same time,the result show that steam treatment,which significantly increased the number seedlings of 1-year-old and 2-year-old Panax quiquefolium L.by 0.81-1.35 times and 6.67-12.0 times respectively,is an environmentally friendly and sustainable development strategy for soil remediation,which will be an important measure to reduce continuous cropping obstacles. |
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