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

Abstract

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 (250mg/L), ampicillin (2.5g/L), penicillin G (2g/L), and Bacicure® (2g/L) provided the highest efficiency in reducing and suppressing the Las-bacterium population indicated by the mean cycle threshold (Ct) values from 20.8 (≈7.2×107cells/g of plant tissue) to 36.6 (≈2140cells/g of plant tissue) in greenhouse experiments, and from 19.4 (≈1.8×108cells/g of plant tissue) to 37.8 (≈969cells/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. © 2014 Elsevier Ltd.