Bacterial leaf blight is a serious disease of rice caused by Xanthomonas oryzae pv. oryzae (Xoo). The objective of this study was to develop a bioformulation of Bacillus velezensis strain N1 by using microencapsulation techniques through spray drying and to then evaluate its performance in controlling rice bacterial leaf blight under greenhouse conditions. Three formulations with a different main carrier were studied and the viability after spray drying, moisture content, characteristic of formulation powder under scanning electron microscope and storage stability were examined. The results showed that formulation 3 (10 % skimmed milk, 20 % maltodextrin, 0.06 % sodium alginate and 5 % tapioca starch) had the highest antagonistic bacterial viability after spray drying of 1.24×107 CFU/g. Formulation 2 had the highest antagonistic bacterial viability of 1.44×106 CFU/g and had the lowest viability reduction of 0.61 Log CFU/g after storage at room temperature for 3 months. Moisture content of each formulation was less than 4 %. Among the 3 formulations of strain N1 bacteria against Xoo, formula 2 was able to control rice bacterial blight disease with the highest disease reduction index (45.87 %). All the results indicated that Bacillus velezensis strain N1 can be an effective antagonist and could potentially be used to develop a more successful bioformulation against rice bacterial leaf blight.
GRAPHICAL ABSTRACT
The efficacy of antagonistic microorganisms and secondary metabolites of entomopathogenic bacteria was evaluated in vitro and in vivo against Xanthomonas oryzae pv. oryzae (Xoo), a causal agent of rice bacterial leaf blight. The effect of the culture filtrates of the microorganisms was tested against Xoo, using the agar well diffusion assay. Trichoderma sp. UB05/3 was the most effective against Xoo. However, the results were not statistically different from those of the entomopathogenic bacterium Serratia nematodiphila GCSR38 with a 22.97 mm and 19.15 mm zone of inhibition, respectively. The effect of the secondary metabolite crude extracts of antagonistic microorganisms (2,000 µg/ml) on Xoo inhibition was tested by the paper disc diffusion method. Only S. nematodiphila GCSR38 was able to control Xoo, with an inhibition zone of 17.60 mm. Minimum inhibitory concentration (MIC) was determined using a 96-well microtiter plate. The MIC of secondary metabolites crude extracts of S. nematodiphila GCSR38 was 1,000 µg/ml and the minimum bactericidal concentration (MBC) was 1,000 µg/ml. The efficacy of the secondary metabolite crude extract of S. nematodiphila GCSR38 against Xoo was tested using the detached leaf technique; the secondary metabolite crude extracts controlled the disease, with 24.45% and 15.56% disease severity when used before and after inoculation with Xoo, respectively. Inoculation with Xoo alone resulted in a disease severity of 44.45%. The secondary metabolite crude extracts of S. nematodiphila GCSR38 can reduce disease severity of bacterial leaf blight in rice by 28.89%, whereas zinc thiazole causes a disease severity of 22.22% and Xoo alone causes a disease severity of 66.67%.
This work aims to develop a multihole atmospheric pressure plasma jet (APPJ) device to increase the plasma area and apply it to a continuous seed treatment system. Broccoli seed was used to study the effects of an atmospheric pressure plasma jet on seed germination and growth rate. An argon flow rate of 4.2 lpm, a plasma power of 412 W, and discharge frequency of 76 kHz were used for seed treatment. The contact angle decreased strongly with the increase in treatment time from 20 s to 80 s. The broccoli seed’s outer surface morphology seemed to have been slightly modified to a smoother surface by the plasma treatment during the treatment time of 80 s. However, the cross-sectional images resulted from Synchrotron radiation X-ray tomographic microscopy (SRXTM) confirmed no significant difference between seeds untreated and treated by plasma for 80 s. This result indicates that plasma does not affect the bulk characteristics of the seed but does provide delicate changes to the top thin layer on the seed surface. After seven days of cultivation, the seed treated by plasma for 30 s achieved the highest germination and yield.
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