| Bacterial leaf blight(BLB),which is caused by the bacterium Xonthomonas oryzae pv.oryzae(Xoo),is one of the most serious diseases in rice.Biological control using antagonistic bacteria or biosynthesized nanoparticles is one of the promising,effective,and safe ways to eliminate or reduce the significant economic losses caused by BLB.To investigate the biocontrol efficiency against Xoo,Paenibacillus polymyxa Sx3(Sx3),which was isolated from the soil of cotton plants and other biosynthesized nanomaterials were applied independently in the current study.Firstly,rice seedling experiments indicated that Sx3 suppressed BLB caused by Xoo and promoted plant growth.The culture filtrate of Sx3 had inhibition effects on the pathogenic bacterial growth,biofilm formation,and cause damage in the cell wall as revealed by microscopic graphs.Moreover,fusaricidins and polymyxin P,two major kinds of secondary metabolites secreted by Sx3,were detected by using MALDI-TOF MS analysis.These metabolites listed as lipopeptides was proposed to play a vital role in the antibacterial activity.In addition,the results showed that Sx3 was able to produce siderophore and amylase but not hydrogen cyanide or proteinase,which might be partially responsible for the inhibitory effect of Sx3 on Xoo.Furthermore,biological tests showed that strain Sx3 was able to fix nitrogen,solubilize phosphate,and produce a significant amount of the hormone(indole acetic acid),indicating that a variety of mechanisms was involved in promoting the plant growth.Secondly,green synthesis of nanoparticles by biological method is an environmental friendly approach due to its biocompatibility and stability.In this study,the biologically synthesized metal oxides nanoparticles(ZnO,MgO,and NiO)and one polymer(Chitosan)were evaluated against Xoo.Different aqueous plant extracts were used to biologically synthesize the above mentioned nanomaterials including Solanum lycopersicium(Green tomato fruits),which have many compounds(polyphenols,carboxylic acid,amino acids,and proteins);while Rosmarinus officinalis(Rosemary leaves)was inferred to contain a large number of flavonoids and phenolic,and Crocus sativus(Saffron stigma)contained a variety of biologically active carotenoids.The obtained nanoparticles were characterized using different biochemical and physics methods such as UV-Visible spectrum,XRD,FT-IR,and EDS,which was used to confirm the presence of the nanoparticles,revealed the crystalline structure and purity.Also,the morphology of the synthesized materials was observed using TEM and SEM.Extracts from these plants played a major role in reducing the nanoparticles and acted as capping agent to enhance the stability of the synthesized nanoparticles.The nanoparticles showed high antibacterial activity against Xoo,which was presented as the significant inhibition on growth,biofilm formation and swimming motility.Treatment with the nanoparticles caused degradation of the cell membrane,induced high reactive oxygen and apoptosis of Xoo cells.Thus,the antibacterial activity of nanoparticles against Xoo is inferred to be mediated by stimulating the reactive cellular oxygen such as hydrogen peroxide,which damages bacterial cells.Furthermore,rice plants treated with NiO nanoparticles promoted the growth parameters presented in(plant height,root height,fresh weight,and dry weight)and inhibited the disease infection represented in percentage diseased leaf area.In summary,Sx3 as a biological agent was evaluated for in vitro and in vivo antibacterial effects against Xoo.Many biological tests were performed to determine and reveal the underlining biological mechanism of Sx3 which enabled it to suppress BLB and enhance rice growth.The nanoparticles showed a notable inhibitory effect on bacteria by combating the casual organism of BLB and promoted the growth of rice.These two contributing factors participate significantly in the biological management of combating BLB. |
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