| American ginseng(Panax quiquefolium L.),which has high medicinal and economic value,is a perennial medicinal plant native to North America.It has many functions such as improving immunity,anti-fatigue,anti-aging and anti-cancer.P.quinquefolium is used as medicine with the roots,and can be harvested after 4-5 years of field growing.During the cultivation of P.quiquefolium,continuous cropping obstacles caused by soilborne diseases and imbalance of soil microbial population and so on,is the main problem threatening the development of American ginseng industry.The rusty root rot of P.quiquefolium caused by Ilyonectria spp.is one of the most common and serious soilborne disease in Liuba County,Shaanxi Province.With the purpose of making the base for the strategy of disease control,and reducting continuous cropping obstacle of American ginseng,from 2019 to 2021,we focused on the occurrence and prevalence of P.quiquefolium rusty root rot and carred out the field investigation,pathogen isolation,determination of pathogens biological characteristics,analysis of pathogen distribution and quantity in soil.The main results are as follows:1.The pathogens of P.quiquefolium rusty root rot in Liuba County of Shaanxi Province was identified based on morphological characteristics,TUB sequence analysis and species-specific PCR.The results showed that there were two pathogens,I.mors-panacis and I.robusta,causing the P.quiquefolium rusty root rot in Liuba.I.mors-panacis was the dominant species with the isolation ratio of 76.7%.The assay of pathogenicity result also showed that the virulence of I.mors-panacis was higher than the virulence of I.robusta.2.The biological characteristics of the two pathogens were compared and analyzed.The results showed that both pathogens appeared weak nutritional selectivity.The rate of mycelial growth and sporulation quantity of I.mors-panacis was significantly lower than the rate of mycelial growth and sporulation quantity of I.robusta.The two pathogens could grow and sporulate normally on different carbon and nitrogen sources.But they had different utilization ratios on different carbon and nitrogen sources.The colony diameters of I.mors-panacis on all carbon and nitrogen sources were smaller than that of I.robusta.Both pathogens can grow and sporulate in the range of 10～30℃.Different temperatures have different effects on the growth and sporulation of various isolates.The optimum temperature for the mycelia growth of both pathogens are 20～25 ℃,but the optimum sporulation temperature varies significantly.The results of p H adaptability showed that both pathogens could grow and sporulate in the range of p H 4-10,and there were significant differences in growth and sporulation under different p H(P<0.05).Under the same p H conditions,the colony diameters of I.mors-panacis was always smaller than that of I.robusta.Slightly acid conditions(p H 6～7)were more suitable for the sporulation and growth of I.mors-panacis.However,I.robusta was more suitable for alkalinity environment(p H 8 for both growth and sporulation).3.In order to monitor the spatiotemporal dynamics and inoculum quantity change of P.quiquefolium rusty root rot pathogens in the soil,and predict the occurrence of rusty root rot,we investigated the spatial distribution pattern and the relative abundane of Ilyonectria spp.in soil.The results illustrated that the optimal sampling method for detected pathogens of P.quiquefolium rusty root rot in soil was chessboard sampling,and the optimal sampling quantity was 10 sample quadrats.In the 0-20 cm layer of American ginseng field soil,pathogens of P.quinquefolium rusty root rot could be aggregated distribution or uniform distribution.The relative abundance of P.quiquefolium rusty root rot pathogens in continuous cropping soil increased with the increase of planting periods and continuous cropping times.Hence,soil disinfection is the key measures for the control of P.quiquefolium rusty root rot. |
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