| The dried root of Astragalus membranaceus(Fisch.)Bge.var.mongholicus(Bge.)Hsiao,a perennial leguminous herb,it is one of the traditional bulk medicinal herbs with high medicinal value and pharmacological effects.Wild A.membranaceus resources can no longer meet the market demand,and artificial cultivation can now alleviate the shortage of resources.A.membranaceus artificial planting is in the initial stage,there are problems such as blindness of fertilization,randomness and low content of active ingredients.Scientific fertilization technology has become one of the main management technologies affecting the yield and quality of A.membranaceus.Compared with soil fertilization,foliar fertilizer has the characteristics of less dosage,less pollution,faster nutrient absorption,and higher nutrient utilization rate,which plays a key role in improving crop yield and quality.Dark septate endophyte(DSE)is a group of endophytic fungi that colonize plant root tissue and form dark,transverse hyphae and micronucleus structures,with similar ecological functions as mycorrhizal fungi,which can establish good reciprocal symbiosis with host plants,promote nutrient uptake and enhance adaptation to adversity.In this study,the A.membranaceus sprayed with different formula foliar fertilizers was used as the research object,and the soil and root samples of A.membranaceus 0-30 cm soil layer were collected during the harvest period.By measuring the growth indexes and effective components of Astragalus,the yield and quality of A.membranaceus under different nutritional regulation were found out;to observe and analyze the symbiotic structure and colonization of DSE fungi in A.membranaceus root,and to explore the relationship between different ecological factors and DSE fungi colonization;DSE fungi were isolated and purified,and the species composition of DSE was identified by morphological and molecular identification methods.At the same time,some strains were selected to simulate drought stress with PEG 6000 to explore the tolerance of DSE fungi to drought stress.so as to provide reference for DSE fungi to play ecological functions in farmland ecosystems.The main results showed as follows:1.Different foliar fertilizer treatments can improve the growth and quality indexes of A.membranaceus root,in which large element fertilizer can promote the biomass of A.membranaceus root,and trace element fertilizer can promote the accumulation of flavonoids in A.membranaceus.The correlation results showed that the medicinal component of A.membranaceus,pistil isoflavone glucoside,was significantly positively correlated with root length,root diameter and root dry weight of A.membranaceus,and formononetin was significantly positively correlated with root diameter of A.membranaceus.2.DSE fungi can highly infect the roots of A.membranaceus to form typical dark septate hyphae and microsclerotium structures,and the colonization rate of hyphae is higher than that of microsclerotia.Across the different treatments,the total colonization rate of DSE fungi averaged was treatment 1(63.23%)> treatment 2(61.15%)> treatment 3(60.50%)> control(34.45%);among different treatments,Chifeng(59.99%)was higher than that of the Baotou(49.68%).3.There were significant differences in the structural characteristics of DSE fungal colonization among different treatments.Among different treatments,the average hyphal spacing in treatment 1(15.11 μm)>treatment 2(14.75 μm)>control(13.89 μm)>treatment 3(13.80 μm),treatment 2 had the highest average hyphal diameter(4.85 μm),and treatment 3had the highest average microsclerotia diameter(7.55 μm).In different sites,the average hyphal spacing(15.01 μm)and hyphal diameter(4.52 μm)of the Baotou were higher than those of the Chifeng,while the microsclerotium diameter(7.43 μm)of the Chifeng was higher than that of the Baotou.4.Correlation analysis showed that soil p H,organic carbon,available phosphorus,alkalihydrolyzable nitrogen,total nitrogen,and available potassium were significantly negatively correlated with DSE colonization.The contents of isoflavone glucoside and formononetin in Astragalus pistil were significantly positively correlated with DSE colonization.The results of ANOVA showed that soil factors and different treatments affected the colonization of A.membranaceus DSE fungi.5.A total of 9 genera and 11 species of DSE were isolated and identified from A.membranaceus root systems of the two sample sites,all of which were ascomycetes.They were Curvularia buchloes、Edenia gomezpompae、Periconia epilithographicola、Poaceascoma helicoides 、 Alternaria doliconidium 、 Paraphoma chlamydocopiosa 、 Fusarium sp.、Dothidotthia symphoricarpi、Magnaporthiopsis panicorum、Cladosporium halotolerans、Cladosporium chasmanthicola The dominant species were C.buchloes,A.doliconidium,Fusarium sp.The isolation frequencies were 14.81%,14.81% and 19.75%,respectively.6.Different concentrations of PEG 6000 were set to simulate drought stress,and it was found that the DSE strain had strong drought resistance.Under solid stress,with the increase of stress concentration,the growth rate of the strain increased first and then decreased,the compartment distance shortened,the mycelial diameter widened,and the structure similar to chlamydospore appeared.Under moderate drought stress,the melanin content of the strain was the highest and the mycelial color was darker.Under high concentration stress,the melanin content of some strains decreased and the mycelial color became lighter. |
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