Isolation and Characterization of a Phage Xoo-Tp1, Infecting Xanthomonas oryzae pv. oryzae

Bacterial leaf blight (BLB), caused by Xanthomonas oryzae pv. oryzae (Xoo), is a major threat to rice cultivation globally, including in Indonesia. Conventional control methods, such as the use of resistant varieties, copper-based compounds, pesticides, and antibiotics, have limitations, including environmental concerns and the development of resistance. Bacteriophages offer a promising alternative as biological control agents due to their high specificity to target pathogens without adverse effects on plants or humans. This study aimed to isolate and characterize the bacteriophages infecting X. oryzae pv. oryzae. Phages were isolated from samples including infected rice leaves, soil from rice fields, and irrigation water in Malang. A bacteriophage designated Xoo-Tp1 was successfully isolated from soil and shown to infect Xanthomonas oryzae pv. oryzae. Xoo-Tp1 exhibited stability at pH 6 to 8, with the highest titer observed at pH 7.0, reaching 4.76 log10 PFU/mL (approximately 5.75 × 104 PFU/mL). No phage activity was detected at pH 5 and pH 9. Temperature stability was observed at 4, 30, 40, and 60 °C, but phage infectivity was no longer detected at 90 °C. Transmission Electron Microscopy (TEM) revealed that phage Xoo-Tp1 possesses an isometric head measuring 171.8 nm in diameter and a tail 94.6 nm in length, consistent with the morphological characteristics of the Myoviridae family. Based on its large size, phage Xoo-Tp1 is suspected to belong to the jumbo phage group. In liquid culture, phage Xoo-Tp1 inhibited the growth of Xanthomonas oryzae pv. oryzae. The 7:1 phage-to-host ratio treatment resulted in the most significant reduction of bacterial cell concentration (44.23%) compared to the untreated control. This study demonstrated that isolated phage Xoo-Tp1 has the potential to be used as a biological control agent in the control of BLB in rice. Further studies are recommended to evaluate its efficacy under field conditions, including phage formulation stability, delivery methods, and host range assessment.