Effect of chemical treatments on ‘Candidatus Liberibacter asiaticus’ infected pomelo (Citrus maxima)

•HLB management in pomelo was achieved using a mixture of antibiotics and Bacbicure®.•Experiments were conducted in the greenhouse and the field.•Recovery of phloem areas was confirmed by TEM.•Morphology of Candidatus Liberibacter asiaticus in sieve element was presented.

Huanglongbing (HLB), also known as citrus greening, is one of the most destructive diseases affecting Rutaceae plants in many parts of the world. HLB is associated with three species of ‘Candidatus Liberibacter’ with ‘Ca. L. asiaticus’ (Las), being the most widely distributed bacterium in Thailand and Asia. The effectiveness of chemical treatment via trunk injection was evaluated in Las-infected pomelo (Citrus maxima) trees using quantitative real-time polymerase chain reaction. Our results demonstrated that a mixture of streptomycin (250 mg/L), ampicillin (2.5 g/L), penicillin G (2 g/L), and Bacicure® (2 g/L) provided the highest efficiency in reducing and suppressing the Las-bacterium population indicated by the mean cycle threshold (Ct) values from 20.8 (≈7.2 × 107 cells/g of plant tissue) to 36.6 (≈2140 cells/g of plant tissue) in greenhouse experiments, and from 19.4 (≈1.8 × 108 cells/g of plant tissue) to 37.8 (≈969 cells/g of plant tissue) in the field experiments. In addition, our strategies remained therapeutically effective for one year. Finally, response of Las-infected pomelo to chemical treatment was elucidated using transmission electron microscopy.