Biocontrol Effect Of Dark Septate Endophytic Fungi On Root Of Pinus.sylvestris Var.mongolica Against Rhizoctonia Solani

Dark Septate Endophytes(DSE)is an important rhizosphere microbial group of plants,which play an important role in promoting plant growth,improving mineral absorption,biological control of diseases,and improving plant resistance.In this study,on the basis of 24 dark-colored endophytic fungi isolated from the roots of P.sylvestris var.mongolica,the highefficiency biocontrol strains that inhibit R.solani were selected through confrontation culture and fermentation broth antibacterial experiments.Through the scanning electron microscopic observation of mycelial interaction,the effect of non-volatile metabolites on the growth and enzyme activity of R.solani and the transcriptome sequencing technology was used to study the inhibitory mechanism of the high-efficiency strain A024(P.bamuru)on R.solani;By measuring the biocontrol effect,biomass index,rhizosphere soil nutrients and bacterial community structure changes,the biocontrol effect of the high-efficiency strain A024,the impact on the 1-year-old seedling growth of P.sylvestris var.mongolica and the rhizosphere micro-ecological environment were analyzed.The main results are as follows:(1)Through ITS sequence determination and phylogenetic tree analysis,the dark septal endophytic fungi on the roots of P.sylvestris var.mongolica mainly include P.bamuru(DSE A002,DSE A024,DSE A083),P.fortinii(DSE A003,DSE H030,DSE H033,DSE H034,DSE H046,DSE H051,DSE J021,DSE J033,DSE J041,DSE J046,DSE J054),A.tamaricis(DSE A028),P.chrysanthemicola(DSE A041,DSE A072),P.radicina(DSE H003,DSE H088,DSE J016),P.sp.(DSE J002,DSE J071,DSE J073)and C.sp.(DSE J018).The strain A024,which has a significant inhibitory effect on R.solani was selected.In the confrontation culture experiment,the inhibition rate of A024 on R.solani was 74.69%.In the fermentation broth antibacterial experiment,the inhibition rate of A024 to R.solani was 69.41%,which could well inhibit the growth of R.solani.(2)In the interaction of the hyphae cultured against each other,the hyphae of the darkcolored endophytic fungus A204 grow spirally and wind around the hyphae of R.solani and then penetrate the hypha to stop the hypha growth and even death.The non-volatile metabolites of A204 can affect the main physiological indicators of R.solani,including CAT,SOD,POD,GSH-Px,MDA and soluble protein.The transcriptome sequencing results of strain A024 induced by R.solani showed that among the differentially expressed genes.1999 unigene were up-regulated and 2546 were down-regulated.A number of functional genes related to biocontrol effects were screened,including endochitinase,serine protease,α/β-hydrolase,heterokaryotic incompatible protein.ABC transporter gene,drug resistance gene-related protein and Heat shock protein and so on.The results showed that the inhibitory effect of P.bamuru A024 on R.solani was related to competition,heavy parasitism,and antibiosis.(3)The inoculation of strain A024 can effectively control the infection of R.solani on P.sy lvestris var.mongolica seedlings,and the control effect is 60.98%.In terms of growthpromoting effect,compared with the control treatment,the fresh weight of the seedlings under the DSE A024 treatment,the height of the above-ground seedlings,the dry weight above the ground,and the dry weight below the ground increased by 17.31%,62.91%,12.09%,40.74%,and 10.43%,respectively.Similarly,the fresh ground weight,ground diameter,seedling height,ground and above-ground dry weight of plants treated with DSE+SH increased by 15.82%,15.71%,43.43%,36.11%,36.11%and 20.83%,respectively.Under the DSE A024 treatment,the nutrient indexes of the rhizosphere soil of P.sylvestris var.mongolica seedlings,including AN,TP,AP,TK,and AK,increased by 57.57%,32.53%,103.84%,33.11%and 23.52%respectively compared with the control.High-throughput sequencing analysis results showed that DSE A024 fungal inoculation changed the rhizosphere microbial community structure of P.sylvestris var.mongolica.RDA analysis results showed that the soil bacterial community structure treated with DSE A024 was positively correlated with AN,OM,AP,AK,TN,and TP.