Biocontrol efficacy of <i>Bacillus licheniformis</i> and <i>Bacillus amyloliquefaciens</i> against rice pathogens

Biocontrol is a cost-effective and eco-friendly approach to control plant pathogens using natural enemies. Antagonistic microorganisms or their derivatives specifically target the plant pathogens while minimizing the harm to non-target organisms. Bacterial blight and brown spot are the major rice diseases caused by <i>Xanthomonas oryzae</i> pv. <i>oryzae</i> (<i>Xoo</i>) and <i>Bipolaris oryzae</i> (<i>Bo</i>), respectively. This study was conducted to assess the plant growth-promoting potential and biocontrol activity of root-associated bacteria against the rice pathogens, <i>Xoo</i> and <i>Bo</i>. A total of 98 bacteria were isolated from rice roots and characterized for plant growth-promoting properties including phosphate solubilization, indole-3-acetic acid production, nitrogen fixation and biofilm formation. Based on these properties, 36 bacteria were selected and tested for biocontrol potential against rice pathogens <i>via</i> co-culturing antagonism assay. LE7 exhibited the maximum inhibition of 79%, while FR8, PE2, LE7, LR22 and LR28 also significantly reduced the growth of <i>Xoo</i>. Likewise, FR2, LR22, LR35 and LE7 significantly inhibited the growth of <i>Bo</i>, in which LR22 exhibited the maximum inhibition of 81%. Under controlled-conditions, LE7 and LR22 significantly reduced the disease incidence of <i>Xoo</i> and <i>Bo</i>, respectively, and improved the growth of rice. Full-length 16S rRNA gene sequencing of most potential bacterial isolates, LE7 and LR22, revealed their maximum identity with <i>Bacillus amyloliquefaciens</i> and <i>Bacillus licheniformis</i>, respectively. Application of <i>Bacillus</i> spp. as biocontrol agent represents enormous potential in rice farming. The most promising bacterial isolates could be used as bioinoculants for rice disease management and improved production in a sustainable manner.