Microbial Antagonists as Bio-Pesticides for Controlling Bacterial Leaf Blight Caused by Xanthomonas oryzae pv. Oryzae

Oryza sativa L. is vulnerable to over 76 diseases, with Bacterial Leaf Blight (BLB) being one of the most prevalent and destructive disease. BLB caused by the pathogen Xanthomonas oryzae pv. oryzae (Xoo), poses a significant threat to rice cultivation globally. The study aims to isolate and characterize potential natural biocontrol agents capable of inhibiting Xoo. Among 115 bacterial isolates, AJS36 showed the highest antagonistic activity, followed by ACS17 and ACS48. Based on 16S rRNA gene sequencing, the isolates were identified as close relatives of Alcaligenes faecalis AJS36 (PQ151613), Enterobacter hormaechei ACS17 (PP998655) and Enterobacter asburiae ACS48 (PP998620). MIC value against Xoo was determined as 2, 4, and 5 µg/mL against AJS36, ACS17, ACS48 respectively. Further, it was observed that the isolates AJS36 and ACS17 significantly reduced biofilm formation, xanthomonadin production, extracellular polymeric substance (EPS) synthesis while inducing cellular protein leakage and enhancing scavenging activity in Xoo in comparison to the isolate ACS48. The potent isolates were sensitive towards various antibiotics like amikacin, levofloxacin, ticarcillin, norfloxacin, ciprofloxacin, tobramycin. Greenhouse trials demonstrated that foliar application of these isolates before Xoo infection significantly reduced lesion length and disease severity under natural conditions, with AJS36 showing the most prominent effect. This is the first report in use of A. faecalis AJS36, E. hormaechei ACS17 and E. asburaei ACS48 as promising candidates to be developed as biocontrol agents for sustainable management of BLB in rice plants and offering alternatives to chemical pesticides.