Mechanisms Underlying The Effects Of Endophytic Fungi Isolated From Elymus Dahuricus On The Drought Resistance Of Wheat

Endophytic fungi play an important role on the growth,physiological metabolism and nutrient accumulation of host plants and they have the capacity to produce bioactive secondary metabolites.Fungal endophytes have a great application potential in agricultural fields such as plant growth promotion,biocontrol agent,heavy metal remediation and abiotic stress resistance enhancement.In this thesis,we have isolated,purified and identified endophytic fungi from Elymus dahuricus inhabited in the arid area of Gansu province and Inner Mongolia,north of China.The endophytic fungi growth characteristics and their capacity of producing plant hormones were tested.The effects of endophytic fungi on wheat plants under drought stress and re-watering conditions were deeply investigated through pots experiments under both greenhouse and field conditions.The targets were to screen the endophytic fungi isolated from the arid areas that are able to enhance the drought tolerance of wheat under the drought stress and re-watering conditions and to reveal the interaction mechanism between the endophytic fungi and wheat plants.The main findings of this thesis are listed as followings:(1)A total of 12 endophytic fungi were isolated from the seeds of Elymus dahuricus.A combination method of colony morphology and ITS rDNA sequences was used to identify these isolated endophytic fungi,5 endophytic fungi were isolated from the seeds of Elymus dahuricus in Gansu province,which turned out to belong to Alternaria alternata.7 endophytic fungi were isolated from Inner Mongolia,among which 5 fungi were categorized to genera Alternaria sp.,while the rest two,LQ141 and LQ144 were categorized to genera Fusarium sp.(2)The growth rates of the LQ1230 and LQ141 strains were fast under normal and drought stress condition,indicating that they could grow normally in arid environment.Endophytic fungi strain LQ1230,LQ2 and LQ141 could secrete indole acetic acid(IAA)via both L-tryptophan-dependent and independent pathway.Specifically,LQ1230 strain has the highest IAA production of 319.24±14.88 ?g/mL and 40.12±8.59 ?g/mL with and without addition of L-tryptophan,respectively.The culture filtration(CF)of the strains LQ1230,LQ1,LQ2 and LQ141 promoted the elongation of coleoptiles by 32.11%,27.45%,47.25% and 48.75%,respectively,and roots by 16.81%,17.52%,35.47% and 34.76%,respectively during the germination of wheat seeds,Additionally,Inoculation of LQ1230 significantly increased the germination rate of wheat seeds and the root length of hydroponic wheat was increased by 27.20% compared to the control,because of which the inhibition effect of drought stress on the growth of wheat could be relieved.(3)Endophytic fungus LQ1230 promoted the growth of wheat plants and significantly increased the biomass of wheat plants.LQ1230 significantly increased the chlorophyll content and root dry weight of wheat under drought stress and rehydration treatment.LQ1230 enhanced the water absorption of wheat plants through significantly increasing the soluble sugars and proline content of wheat plants under drought stress,and reduced the malondialdehyde(MDA),which resulting in alleviation of the inhibition effect of drought stress on wheat growth.Furthermore,LQ1230 increased the activities of antioxidant enzymes POD and CAT of wheat plants under drought and rehydration conditions.LQ1230 also inhibited the decrease of photosynthesis rate and increased the photosynthetic efficiency of photosystem II under drought stress and rehydration treatments.LQ1230 significantly increased the C and N accumulation of wheat,and the significant positive correlation between the C,N accumulation and the plant biomass were observed.(4)Endophytic fungi LQ1230,LQ2 and LQ141 promoted the growth of wheat plants at the late growth stage under various water treatments,where significantly increases on the shoot dry weights by 23.48% ~21.74%,root dry weights by 26.93% ~29.63% and plant height by 4.23% ~9.41% were achieved respectively.Endophytic fungi enhance the drought resistance and recovery capacity of wheat through promoting the net photosynthesis rate and water use efficiency of wheat plants under drought stress and rehydration treatment.In addition,the N accumulation of fungal endophyte inoculated wheat plants under drought stress and rehydration increased by an average of 49.62% and 22.85%,respectively.The promotion of N accumulation was more apperent under drought stress.Endophytic fungi LQ1230,LQ2 and LQ141 significantly increased the Zn concentration in wheat shoots and roots by 70.77% and 27.20%,respectively compared to the control.The yields were increased by 22.57%,23.96% and 14.24% compared to the control,respectively.In conclusion,endophytic fungi from Elymus dahuricus promoted wheat growth and improved the osmotic adjustment ability,antioxidant enzyme activity and photosynthetic parameters,as well as enhanced the carbon,nitrogen and zinc accumulation and the yields of wheat under drought stress and rehydration treatments.Upon these facts,the drought resistance and recovery capacity after re-watering of wheat were consequently strengthened with the endophytic fungi colonization.