Pathogen identification, bactericide-resistance determination, and control efficacy evaluation of the biocontrol bacteria for rice bacterial leaf wilt

Objective Bacterial leaf blight caused by Xanthomonas oryzae pv. oryzae (Xoo) is a globally important disease that harms rice worldwide. In recent years, Pantoea ananatis and Enterobacter spp. have been discovered to cause rice bacterial leaf wilt and have a serious impact on rice production. This study aims to isolate and identify the pathogens of rice bacterial leaf wilt in Guangdong and other places in recent years to clarify the prevalent pathogenic species in the field, and conduct conventional bactericide resistance tests on the main pathogens to clarify the reasons for the frequent occurrence and difficulty in field disease control. Meanwhile, the study isolates and screens healthy foliar microorganisms to obtain antagonistic bacteria with potential biocontrol efficacy to provide beneficial microbial resources and alternative disease prevention strategies for field prevention and control of the disease.

Method Rice samples from Guangdong and other places were collected and the leaves were subjected to microbial isolation using tissue isolation method. The bacteria were identified in combination of colony morphology, physiological and biochemical characteristics and housekeeping gene sequences, and their pathogenicity was determined by inoculation tests to verify Koch’s Rule. Gradient dilution culture method was performed to evaluate the resistance of the pathogens to five commonly used bactericides by measuring the minimum inhibitory concentration (MIC). Antibacterial zone method was applied to determine the antagonistic activity of bacteria against the pathogens, and their biocontrol potential against the disease was clarified through pre- and simultaneous inoculation.

Result The bacterial communities isolated from diseased rice leaves in multiple locations and batches were diverse, with P. ananatis accounting for the largest proportion (21.95%). The bacterial groups from healthy leaves were relatively limited, with Bacillus spp. accounting for 52.46%. Xoo, P. ananatis, and E. pseudoroggenkampii had developed resistance to kasugamycin, chloroisobromine cyanuric acid, thiazole zinc, and thiamethoxam, while zhongshengmycin had a good broad-spectrum antibacterial effect on the three pathogens. The application of B. amyloliquefaciens, B. subtilis, and B. velezensis could effectively reduce the occurrence of diseases.

Conclusion P. ananatis has become the primary pathogen of rice bacterial leaf wilt in the field. The emergence and co-infection of multiple pathogens make disease prevention and control more complex. Long term and extensive use of the chemical pesticides cause multiple bactericide resistance of the pathogens. Therefore, studying the pathogenic mechanism of newly prevalent pathogens of rice bacterial leaf wilt and developing new efficient and safe measures, especially screening and using beneficial foliar culturable microorganisms, are crucial for effective disease prevention and control.