Biochemical characterisation and in vitro mitigation of Xanthomonas citri pv. punicae, causing bacterial blight in pomegranate, using antibiotics and copper compounds

Bacterial blight, caused by Xanthomonas citri pv. punicae (Xcp), severely impacts the global pomegranate industry, with alarming yield losses up to 80%. This pathogen becomes a glitch in the pomegranate industry, leading to reduced commercial pockets globally, especially in Pakistan. The objective of this study was to conduct biochemical characterisation and in vitro evaluation of copper compounds and antibiotics against Xcp, for optimal fruit quality and yield. The pathogen was isolated from infected tissues of the pomegranate, and various biochemical tests were performed to identify the bacteria. Pathogenicity was confirmed using the pin-prick and infiltration method on cv. Golden. The in vitro efficacy of antibiotics and copper compounds was assessed using the disk diffusion method against Xcp. The pathogen was aseptically cultured via the streak plate method, and disks impregnated with different chemical concentrations were placed on solidified media. A control disk was treated with sterile water containing 1% v/v surfactant. Plates were incubated at 28 ± 2 °C for 48 and 72 h to observe bacterial growth inhibition. Biochemical analysis showed positive results for the oxidase test, catalase test, KOH solubility test, gelatin liquefaction, and starch hydrolysis test, while Gram staining was negative. Antibacterial efficacy was determined by measuring inhibition zones after 48 and 72 h of incubation. The highest inhibition zones, measuring 29.55 mm and 37.73 mm at 48 and 72 h, respectively, were recorded with 550 µg/ml oxytetracycline hydrochloride, followed by streptomycin sulfate (550 µg/ml) with zones of 29.12 mm and 32.42 mm. In contrast, copper-based compounds, particularly copper sulfate (2000 µg/ml), exhibited the lowest inhibition, with zones of 8.85 mm and 8.86 mm at the respective time intervals. A comparative analysis demonstrated that antibiotics showed outstanding and prodigious results compared to copper compounds. The results of this experiment demonstrate the effectiveness of oxytetracycline hydrochloride and streptomycin sulfate in inhibiting the radial growth of Xcp under controlled conditions. Furthermore, changes in dosage/concentration, time of application, and field application method may help researchers with field-oriented results in the future.