Effect Of Straw Returning On Soil Microbes In Paddy Fields And Biocontrol Potential Of ZY-1 Strain Against Rice Sheath Blight

Rice-wheat rotation is used mainly on rice cultivation in Zaoyang City,Hubei Province.To explore the effects of straw returning on microbial diversity in rice rhizosphere soil and occurrence of rice sheath blight,Illumina high-through sequencing technology combined with related bioinformatics analysis were used to analyze the difference of microbial diversity in rice rhizosphere between straw returning paddy field(SRPF)and non-straw returning paddy field(NSRPF),and real-time fluorescence quantitative PCR(RT-q PCR)was conducted to investigate the accumulation of Rhizotonia solani in paddy field under the rice-wheat cropping system.A strain of bacterium ZY-1 was isolated from the rice rhizosphere of SRPF.The biocontrol strain was identified,genes related to antimicrobial peptide synthesis was detected and the antifungal lipopeptides were extracted and analyzed.And biocontrol potential of the strain ZY-1 was evaluated.The results were described as follows:1.Available N,P and K were all found to be increased in SRPF and the contents of available N and K were significantly increased by 10.50% and 26.32%,respectively,in booting stage.The richness and diversity of bacterial community in rhizosphere soil of SRPF were higher than those of NSRPF,and the increase of richness was significantly changed.The diversity of fungal community in rhizosphere soil of SRPF was lower than that of NSRPF,whereas the diversity was slightly higher.At the phylum level,Proteobacteria,Actinobacteria,Chloroflexi and Acidobacteria were found to be the dominant bacteria phyla in rhizosphere soil of both two treatments,while Ascomycota,Zygomycota and Basidiomycota were found to be the dominant fungi phyla.SRPF and NSRPF shared 595 bacterial genera and 126 fungal genera,while SRPF contained 123 unique bacterial genera and 41 unique fungal genera.At genus level,SRPF significantly increased the relative abundance of Nitrospira and Bacillus by 96.11% and 106.19%,respectively,but significantly decreased the relative abundance of Sphingomonas and Pseudarthrobacter by 32.13% and 77.47%,respectively(P < 0.05).Meanwhile,the relative abundance of Alternaria and Pyrenochaetopsis of SRPF were 1.59% and 1.40%,respectively,which were significantly lower than those of NSRPF(P < 0.05).Incomparison to NSRPF,SRPF significantly increased the accumulation of R.solani in paddy field by 120.20%in booting stage.In SRPF,the disease index of rice sheath blight was increased by 18.10%-45.41%.2.The biocontrol strain ZY-1 was isolated from the rhizosphere soil of the rice plant in SRPF.ZY-1 showed a wide antimicrobial spectrum and its culture filtrate significantly inhibited mycelial growth of R.solani with mycelial abnormal swelling and disintegration.It was identified as Bacillus subtilis through morphologic observation,Biolog identification system and 16 S r DNA sequence analysis.PCR showed ZY-1 contained 17 antimicrobial peptide synthesis related genes,including fengycin(fen A,fen B and fen D),iturin(ITUDI,itu D and itu A),bacillomycin(bmy B,bmy D and BAMC),bacilysin(BACD,BACAB and BAC),bacisubin(hag and tas A),ERISA,surfactin(srf AD)and polymyxin(pmxc).The expression of nine peptide synthesis genes,encoding fengycin(fen B),iturin(ITUDI),bacillomycin(bmy D and BAMC),bacilysin(BACD,BACAB and BAC)and bacisubin(hag and tas A)was revealed by RT-PCR.Fengycin(Fengycin B)and iturin(Bacillomycin D)were the main components of lipopeptides in its culture filtrate by liquid chromatography-mass spectrometry(LC-MS).The antagonistic substances from culture filtrate of ZY-1 had high thermal stability,Uv tolerance and alkali resistance,but showed low acid resistance.Both in vitro and pot experiments showed that the control efficacy of culture filtrate of ZY-1 strain against rice sheath blight exceed 70.00%.In conclusion,the contents of available soil nutrients elements,the richness of bacterial community in rice rhizosphere soil and the accumulation of R.solani in paddy field were significantly increased in SRPF.The rice sheath blight occurred more severely compared to NSRPF.ZY-1 strain was found to produce antifungal lipopeptides and showed good control efficacy against rice sheath blight.