Study On The Diversity Of Endophytic Fungi In Oat And The Drought-resistant And Growth-promoting Characteristics

With the global warming,the duration and frequency of drought increase,which is not conducive to the sustainable development of agriculture,a serious threat to food security.Endophytic fungi are important microbial resources,which can promote plant growth,resist abiotic stress,produce a variety of metabolites,and improve plant yield.Oat(Avena sativa L.)is a special food and forage crop in Inner Mongolia,which is mostly grown in the northern foothills of Yinshan Mountain.In this study,we isolated and purified endophytic fungi from leaves and stem of oat seedlings planted in the northern foot of Yinshan Mountain to explore the diversity of endophytic fungi in oat.Through auxin production,different concentrations of PEG-6000 and seed germination experiments,strains with growth promotion and drought resistance were screened out from oat endophytic fungi.Combined with pot experiment in greenhouse,simulated drought stress,from the level of osmotic regulation,anti-oxidation,photosynthesis,hormonal changes and levels of metabolites,explore the endophytic fungi-oat symbionts in adapt to drought stress cause the mechanism of action,further excavate the function of endophytic fungi of oats,In order to provide theoretical basis for improving agricultural productivity and crop breeding.The main results are as follows:1.Seventy-four endophytic fungi were isolated and purified from oat stems and leaves by traditional media.Combined with morphological identification and ITS molecular identification,the isolation rates of endophytic fungi from stems and leaves were 17.50%and 28.22%,respectively.These endophytic fungi belonged to Ascomycota and Basidiomycota.The dominant endophytic fungi were Alternaria sp.(32.14%)in the stems,and Fusarium sp.(54.35%)in the leaves.2.Five endophytic fungal strains with drought resistance and growth promotion function were screened by means of tryptophan medium,PEG-6000 medium and seed germination method,which were O-2,O-51,O-63 and O-66.Under 12%PEG-6000 drought stress,inoculation of endophytic fungi increased aboveground biomass(2.05%26.49%)and promoted root growth of oat.The total root length,total root surface area,total root volume and root tip number were significantly increased by 20.40%,28.48%,38.46%and 59.24%by O-66 inoculation compared with those without inoculation,respectively.3.Inoculation of endophytic fungi O-2,O-51,O-63 and O-66 promoted the growth of oat under different water treatments.Under drought stress,inoculation of O-2 and O-51 significantly increased plant height,dry weight above ground and dry weight of root of oat.Compared with the control,they increased by 33.69%,46.60%,79.72%and 29.63%,60.87%,87.82%,respectively.Under drought stress,O-2,O-51,O-63 and O-66 increased the activities of SOD,POD,CAT,GR,APX and PLA in oat leaves,increased the contents of antioxidant GSH and AsA,decreased the contents of H2O2 and OFR in leaves,decreased the content of MDA,and protected cell membrane.Inoculation of endophytic fungi O-2,O-51,O-63 and O-66 also increased the contents of free proline,soluble sugar and soluble protein,among which O-2 and O-66 had a significant effect on osmotic regulator under drought stress.Inoculation of endophytic fungi increased leaf SPAD under drought stress,and improved photosynthetic performance of oat leaves.Pn,Gs and WUE were significantly increased under severe water stress,while Ci was significantly decreased,which improved photosynthetic efficiency of photosystem PSII.4.At the late growth stage(heading stage),inoculation with endophytic fungi O-2,O51,O-63 and O-66 could Promote oat growth.After inoculation with endophytic fungi,the photosynthetic rate and stomatal conductance of oat were increased by increasing SPAD and PSII of photosynthetic system under drought stress,and then the dry matter accumulation of oat was increased.In addition,inoculation with endophytic fungi O-2,O51,O-63 and O-66 significantly increased the contents of auxin(IAA)(7.96%-21.73%)and GA3(4.98%-43.27%)in oat under drought stress,while there was no significant difference in the changes of zeatin nucleoside(ZR)and abscisic acid(ABA).Promotes the absorption of nutrients in oat.Inoculation of endophytic fungi O-2 and O-66 significantly increased the accumulation of nitrogen and phosphorus in the upper soil under drought stress,which the times were 1.03,1.06 and 1.14,1.18,respectively.5.Inoculation of endophytic fungi O-2,O-51,O-63 and O-66 increased oat yield under different water treatments.Under drought stress,inoculation of O-2,O-51 and O-66 significantly increased spikelets per plant and grains per spike,but had no significant difference in 100-grain weight of oat.Under drought stress,o-2 and O-51 inoculation significantly increased grain yield by 2.20 times and 1.72 times,respectively.6.A total of 1016 metabolites were detected in the leaves of inoculated endophytic fungi and uninoculated oat under different water treatment by UPLC-MS/MS.Compared with normal water treatment,organic acids,sugars and alcohols in leaves of uninoculated oat were up-regulated under drought stress,while endophytic fungi mainly up-regulated the content of saphenol,and all other products were down-regulated.Compared with noninoculated fungal treatment,inoculated endophytic fungi down-regulated lipids in normal water treatment,and up-regulated flavonoids,alkaloids and flavonols in drought stress.