Preliminary Studies On The Allelopathy Of Medicinal Plant Scutellaria Baicalensis Georgi

Autotoxicity,a kind of intraspecific allelopathy,is defined as a process in which a plant releases toxic chemicals to inhibit or delay germination and growth of other plants of the same species.Autotoxicity is verified to obstacle to continuous cropping and causes regeneration failure in crop growth and yield.However,whether autotoxin impacted soil microbes and thus resulted into continuous obstacle are kept not-well known.Here,we used medicinal plant Scutellaria baicalensis Georgi as an experimental plant to test hypothesis that allelochemicals released by S.baicalensis negatively affect the source plant by inducing autotoxicity and by increasing pathogen population and decreasing beneficial arbuscular mycorrhizal fungi in the soil.Regarding autotoxicity and allelophathic substances in root exudates as the most important factors in continuous cropping obstacles,we determined the autotoxicity and the dynamics of rhizosphere microbial populations,e.g.AMF and soil-borne pathogens.The effect of crude root exudates and baicalin on S.baicalensis seedlings and soil-born pathogens hypha growth was also tested.The main results obtained were as follows:1 Autotoxitic effect of root exudates on S.baicalensisBoth the baicalin(0.97ppm) and crude root exudates(5.82ppm) of S.baicalensis significantly inhibited seed germination of S.baicalensis.In the sands in which S.baicalensis had been cultivated before,the seed of S.baicalensis performed a lower germination and higher death rate in in situ experiment.The damping-off seedlings were found in this treatment.When S.baicalensis was planted in the continuous cropped soil sampled from Shandong Province S.baicalensis-producing area,the average plant height and aboveground biomass showed a significant decrease than that grown in non-continuously-cropped soil.The underground part biomass of the plant decreased much more significantly.2 Accelerating effect of AMF on the growth of S.baicalensisWith the addition of sole AMF Glomus mosseae,no promoting effect was detected in the growth of S.baicalensis.With the addition of combined AMF(Glomus mosseae,Glomus versiforme,Glomus diaphanum,Glomus geosporum),the average plant height,shoot biomass and underground biomass of the plants has increased significantly.AMF natural colonization rate in S.baicalensis in the field was detected out from 15%to 45%.Spore numbers existing in 50g dry soil were detected between 30 and 120.3 The nutritional elements status in S.baicalensis continuous cropped soilsOrganic matter content(17.17g/kg) and total nitrogen(0.96g/kg) in continuous cropped soil was slightly lower than that in the non-continuously-cropped soil(20.15g/kg) and(1.16g/kg),respectively.Other nutritional elements,such as available phosphorus and available potassium,were higher than that in the control soil.Spore numbers of AMF in continuous cropped soil was significantly less than that in the control.4 The soil-borne pathogens significantly restrained the growth of S.baicalensisTwo kinds of commonly existing soil-borne pathgens,Pythium ultimum and Rhizoctonia solani,significantly inhibited the germination of S.baicalensis seed,increased damping-off rate and mortality of S.baicalensis seedlings.P.ultimum performanced greater harmful effect on the growth of S.baicalensis than R.solani did.5 Root exudates of S.baicalensis inhibited the formation of mycorrhizae and promoted soil-borne pathogens infectionBoth 70%ethanol roots extracts of S.baicalensis and the two-years-continuouslycropped soil which containing S.baicalensis root exudates,significantly inhibited the AMF colonization in the plants.Both crude root exudates of S.baicalensis and baicalin stimulated the activity of P.ultimum and R.solani.Plate culture experiment showed that the pomoting effect of crude root exudates on soil-borne pathogens was greater than that of pure baicalin.6 AMF inhibited the activity of soil-borne pathogensWith the addition of combined AMF community(Glomus mosseae,Glomus versiforme, Glomus diaphanum,and Glomus geosporum),the disease infection rate of S.baicalensis showed a significant decrease.As a conclusion,the mechanism for phytoautotoxicity of S.baicalensis might be described as:(1)Firstly,the root exudates of S.baicalensis have a directly autotoxitic effect on its own growth;(2) Meanwhile,they inhibited AMF which were beneficial for S. baicalensis's growth;(3) Futhermore,the autotoxins promoted the activity of soil-borne pathogens which was harmful for S.baicalensis.