Screening of Endophytic Bacteria as Biocontrol Agents Against Bacteria Leaf Blight (Xanthomonas oryzae)

Bacterial leaf blight (BLB) is one of major threats in rice production as it can cause 100% yield loss. Concern on the environment and human health has led an attempt to replace existing methods of chemical control and avoid extensive use of bactericides by using endophytic bacteria. The present study was conducted to screen and characterize bacteria isolated from different sources that has potential as antagonistic bacteria against Xanthomonas oryzaepv. oryzae (Xoo), the causal agent of bacterial leaf blight of paddy. Two hundred and thirty-three endophytic bacteria were successfully isolated from roots and leaves from paddy field. Only 17 endophytic bacterial isolates showed positive antagonistic activity indicated by inhibition zone around bacterial colony against Xoo on nutrient agar plate with 2 endophytic isolates (BCA 3 and BCA 12) showed highest inhibitory effect with 35±0.00 mm in diameter. Molecular identification by 16S rRNA amplification successfully identified the antagonistic endophytic bacteria as Pseudomonas fluorescensand Geobacillus thermoparaffinivorans. Findings in this study revealed the biocontrol abilities of isolated endophytes as an excellent option to be used by agriculture sectors to have sustainable environment

Fluorescence-based immunoassay for the detection of Xanthomonas oryzae pv. oryzae in rice leaf

The identification of rice bacterial leaf blight disease requires a simple, rapid, highly sensitive, and quantitative approach that can be applied as an early detection monitoring tool in rice health. This paper highlights the development of a turn-off fluorescence-based immunoassay for the early detection of Xanthomonas oryzae pv. oryzae (Xoo), a gram-negative bacterium that causes rice bacterial leaf blight disease. Antibodies against Xoo bacterial cells were produced as specific bio-recognition molecules and the conjugation of these antibodies with graphene quantum dots and gold nanoparticles was performed and characterized, respectively. The combination of both these bio-probes as a fluorescent donor and metal quencher led to changes in the fluorescence signal. The immunoreaction between AntiXoo-GQDs, Xoo cells, and AntiXoo-AuNPs in the immuno-aggregation complex led to the energy transfer in the turn-off fluorescence-based quenching system. The change in fluorescence intensity was proportional to the logarithm of Xoo cells in the range of 100–105 CFU mL−1. The limit of detection was achieved at 22 CFU mL−1 and the specificity test against other plant disease pathogens showed high specificity towards Xoo. The detection of Xoo in real plant samples was also performed in this study and demonstrated satisfactory results