| Rice blast is one of the most destructive disease affecting the sustainable development of rice industry,which poses an important threat to global food security.Using endophytes to control crop diseases and regulate crop growth is one of effective measures in crop integrated disease management.In this study,a Bacillus cereus strain YN917 was isolated and identified from healthy rice plants in Taojiang nursery of Hunan Province.The effects of growth promoting on rice and control of rice blast of the strain were estimated.Main results are showed as follows:An endophyte strain,YN917(CCTCC No.2020655.1),which has a significant inhibiting efficacy of 72.63% ± 1.30% on Magnaporthe oryzae,was isolated from Xiangzaoxian No.24 healthy rice leaf by dilution plate method.Strain YN917 was identified as B.cereus by morphological characteristics,physiological and biochemical characteristics and 16 S r RNA sequence analysis.YN917 could inhibit the mycelium growth and conidium germination of M.oryzae,and change the morphology of mycelia,leading to swell and twist,and then dissolving the mycelia and inhibiting conidia formation.YN917 also was positive for production of indole-3-acetic acid(IAA),ACC deaminase,siderophores,phosphatesolubilizing enzyme and other major enzymes including protease,amylase,cellulase and β-1,3-glucanase.Strain YN917 had significant effects on disease prevention and growth promotion,and could promote seed germination and enhance the growth status of rice seedlings.When seeds were soaking treated with YN917,the plumule length and radicle length were increased 101.54%and 77.32%,respectively.Application of strain YN917 could significantly increase the plant height,stem width,root length,fresh weight and dry weight by 48.74%,17.39%,157.72%,30.29% and 35.71%,respectively,the chlorophyll content,root activity and defense enzyme activities were significant increased,which could induce rice defense response,and show a significant control effect on rice blast.The strain YN917 was proved to be effective in preventing and promoting the growth of rice blast through leaf inoculation in vitro,greenhouse pot spray inoculation and 2 years field experiment.Application of in vitro inoculation with strain YN917 on surface of 5-leaf stage rice leaves could reduce the incidence of rice blast,with a control efficiency of 79.33% to 85.89%.There was no significant difference between the control effect of YN917 and the chemical control 20% tricyclazole WP on the control efficiency against leaf blast and panicle blast.The whole genome of strain YN917 was sequenced using Illumina Hiseq II platform and Pac Bio RS III platform(Access number PRJNA687285).Its genome was composed of a52,60245 bp ringlike chromosome and a 65,917 bp endophytic plasmid.The total length of the genome was 532,6162 bp,with average GC content of 35.37%,potentially containing 5483 genes,105 t RNA,42 r RNA,178 tandem repeats,3 prophages,9 genomic islands.Multiple genes associated with disease prevention and plant growth promoting were found in the genome of YN917 by COG,GO and KEGG analysis.In addition,many organic acid synthesisrelated enzymes closely related to the phosphorus solubility in the pathways of carbon metabolism were detected in the YN917 genome.Several genes related to siderophores were found in ABC transport metabolism,cellular porphyrin and chlorophyll metabolism pathways.Moreover,genes related to IAA synthesis were found in tryptophan metabolic pathway.Six secondary metabolite synthesis gene clusters encoding bacteriocin,siderophore,NRPS,terpene and other antibacterial substances were predicted.The optimal ammonium sulfate saturation for the precipitation of the antifungal protein produced by strain YN917 was determined to be 80%.This protein had a wide antifungal spectrum and a high temperature resistance,and was insensitive to p H,ultraviolet radiation and proteases K,but sensitive to trypsin and pepsin.LC-MS/MS analysis confirmed that the strain YN917 can produce molybdenum cofactor.In conclusion,B.cereus YN917 could be use as biocontrol agent to control rice blast,and this study also provides theoretical guidance for further rational use of biocontrol agent resources. |
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