Effects Of Root Exudates From Different Crop Rotation On Root Rot Pathogen Of The Astragalus Membranaceus (Fisch.) Bge.Var.Mongholicus (Bge.) Hsiao

Root exudates plays a key role in communication between plants and microbes in the rhizosphere,many plants are found to resist potential soil-borne pathogens by releasing antimicrobial activity chemicals to the rhizosphere in root exudates.Continuous cropping obstacles reduce the yield and quality of Astragalus mongholicus.Root rot caused by Fusarium is one of the main reasons,the use of pesticides will cause environmental pollution,and crop rotation is a green approach.It is important to evaluate the interaction between root exudates from the different crops and the pathogen and thus to clarify the mechanism of disease suppressiveness in the rotation cultivation.First of all,the main pathogens of Astragalus root rot were isolated and identified.After that,the effects of the root exudates on the growth of the main pathogens were studied in the three different rotation crops of naked oats,rapeseed and buckwheat.The results are as follows:1.Two major pathogens,Fusarium oxysporum f.sp.and Fusarium solani,were identified by morphological observation,rDNA ITS molecular identification and pathogenicity detection.2.The crude extracts of crop rotation rapeseed,buckwheat and naked oats roots were collected by the method of leaching.Compared with the control,the crude extract of naked oats root exudates had an obvious inhibitory effect on Fusarium solani and Fusarium oxysporum f.sp.The root exudates of rapeseed had an obvious growth promotion effect on these two pathogens,and buckwheat root secreted had no obvious effect.3.GC-MS analysis showed that the essential components of naked oats and buckwheat root secretions were mainly alkanes,low-molecular-weight acids,phthalates,etc.,which existed some differences in the composition of root exudates of rapeseed.The three ester compounds selected were dibutyl phthalate,1,2-Benzenedicarboxylic acid,bis(2-methylpropyl)ester,1,2-Benzenedicarboxylic acid,butyl octyl ester,and two acid compounds such as phthalic acid and benzoic acid were used for experimental that mycelial growth inhibition experiments and spore germination experiments.The inhibitory effect was increased with the increase of concentrations of 0.0,0.2,0.4,0.8,and 1.6 mg/mL.Furthermore,the addition of the external compounds phthalic acid and benzoic acid had a significant inhibitory effect on the mycelial growth and spore germination of the pathogen.From the perspective of root exudates,our experiment clarified the mechanism by which Astragalus and naked oats rotation can ameliorate the pathogens causing root rot of Astragalus.It is speculated that there are some antibacterial substances in root exudates of naked oats,which have inhibitory effects on the growth and reproduction of soil pathogens.This experiment is of great significance for the prevention and treatment of root rot of Astragalus,providing a new defensive measure for the standardized cultivation of Astragalus.