| Xanthomonas oryzae pv.oryzae(Xoo)and Acicdovorax oryzae(Ao)are bacterial plant pathogens causing bacterial leaf blight(BLB)and bacterial brown stripe(BBS),respectively.Chemical treatments on these pathogens have resulted in the accumulation of chemicals or increasing of antibiotic-resistance of Xoo or Ao.Thus,rendering the traditional chemicals or antibiotics ineffective in protecting plants or managing diseases outbreak.Also,the environmental unfriendliness accompanied by the use of these chemicals makes it a need of the hour to develop environmentally safe strategies in combatting bacterial crop diseases.Biological methods have proven to be an effective,durable,and eco-friendly approach in combatting these diseases.A total of 5 Xoo bacteriophages(X1,X2,X3,X4,and X5)were isolated from diseased rice plants from the fields of Guangdong,Zhejiang,and Liaoning province.The phages were grouped into the order Caudoviridae and family Myoviridae based on the possession of icosahedral head,necks,contractile tails,base plates,and tail fibers regarded.The phages have double-stranded DNA nucleic acid type and based on the phylogenetic analysis of the DNAP gene,which was found to be related to Xanthomonas phage OP2.Phage X3 had the longest latent period of 40 min with the least burst size of 50 PFU/cell and had the broadest host range in that it causes the lysis of 22 strains out of the 23 tested Xoo strains.The phages significantly reduced the exopolysaccharide(EPS)production and biofilm formation of strain GZ 0011.The phage X3 caused 53%degradation in EPS production and degraded the biofilm formation by 43%.BLB disease severnty in vivo was significantly reduced by 83.1%when phage X3 was sprayed before pathogen inoculation while seed treatment with phage X3 was very effective and the best treatment for managing BLB was 95.4%reduction of disease severity.The isolated phages were efficient biological control agents in the control of BLB.ZnO,MgO,CuO,and MnO2 nanomaterials were bio-synthesized using rhizophytic bacteria Paenibacilhis polymyxa strain Sx3,Xoo bacteriophage X3 lysate,plant extracts of flowers of chamomile(Matricaria chamomilla L.),leaves of olive(Olea erropaea),fruits of red tomato(Lycopersicon esculentum M.),and flowers of hibiscus(Hibiscus rosa-sinensis).The obtained nanomaterials were characterized using UV-Visible spectroscopy,Fourier transform infrared spectroscopy(FTIR),X-ray diffraction(XRD),transmission electron microscopy(TEM)and scanning electron microscopy(SEM)with energy dispersive spectrum(EDS)profile.The resultant nanomaterials were checked for their antibacterial efficiency,biofilm formation,growth,and swimming motility impact on Xoo and AoThe peak absorbance of ZnO,MgO,and MnO2 nanomaterial synthesized by P.polymyxa was 385,215,and 230 nm with an average dominant crystallite size of 62.8,18.8,and 10.9 nm for ZnO,MnO2 and MgO,respectively.The general structural observations of the ZnO were cubic,MgO had a flowered shape(nanoflower),and MnO2 were spherical.The application of ZnO,MnO2,and MgO nanomaterial synthesized by P.polymyxa respectively,decreased Xoo biofilm formation by 74.5,74.4,and 80.2%and had an inhibition zone of 1.7,1.3 and 1.3 cm at 16.0 μg/ml.Among the three plant extracts used to synthesized ZnO nanomaterials,synthesis by Olea europaea at 16.0μig/ml was found to have the highest significant antibacterial efficiency against Xoo having a bacterial inhibition zone of 2.2 cm,bacterial growth reduction of 67.5%,biofilm formation reduction of 83.3%and a 48.5%decrease in halo diameter.The excellent antibacterial efficiency was attributed to its dominant crystallite small size of 48.2 nm as compared to others.The growth of Ao strain RS-2 was decreased by 62.9 and 71.3%,and had a clearing diameter of 1.8 and 2.3 cm,respectively,after treatment with MgO and MnO2.Also,the apoptotic cell ratio of Ao increased from 0.97%to 99.52 and 99.94%when treated with MgO and MnO2 nanomaterial,respectively.At 200.0 μg/ml CuO,MgO,and MnO2 nanomaterials significantly inhibited the growth of Xoo,respectively,by 79.65,77.78 and 71.47%and biofilm formation,respectively,by 79.17,75.77 and 76.72%.The nanomaterial experiment of nano-zinc,nano-magnesium,nano-manganese,and nano-copper revealed that each of the nanomaterials significantly inhibited the bacterial growth,biofilm formation,and swimming motility of Xoo and Ao in a concentration-dependent manner.The nanomaterial had an efficient antibacterial activity by antagonizing the bacterial on plate assay with its antibacterial mechanism inferred to be cell membrane damage causing loss of intracellular contents and production of reactive oxygen species.Treatment of Xoo infected rice plants with 200.0 μg/ml CuO,MgO,and MnO2 nanomaterial significantly increased the plant growth and biomass compared to the Xoo infected plants alone.CuO nanomaterial treatment resulted in significant disease suppression of 24.12%DLA compared to the infected control of 75.20%DLA while disease suppression of 15.04 and 21.86%,respectively,for MgO and MnO2 nanomaterials treatment,were observed as against the control of 75.79%DLA.The maximum efficiency of the photosynthetic apparatus(Fv/Fm)of Arabidopsis plants treated with CuO,MgO,and MnO2 nanomaterials was within the range of 0.80-0.85 which indicates that the nanomaterials had no stress-suffered impact on the plant physiological status.The effective quantum efficiency of PSII photochemistry in the light((?)PSⅡ)of of Arabidopsis plants treated with CuO,MgO,and MnO2 nanomaterials was positively increased compared to the control while the non-photochemical energy dissipation((?)NPQ)was decreased in the treated plants.Also,the chlorophyll synthesis and photosystem structure genes of Arabidopsis plants were significantly increased as a result of the treatment with CuO,MgO,and MnO2 nanomaterials.In summary,23 Xoo strains and 5 phages were isolated from diseased rice plants in the field of 3 provinces in China.The phages were found to be effective in the management of BLB.in vivo and in vitro.The use of biologically synthesized nanomaterials was found to be an effective agent in the management of BLB and BBS without having any toxic effect on the plants and function as nano-fertilizer and nano-pesticide.Therefore,these findings contribute to the biological and other control management of BLB and BBS diseases. |
