D3262: Nano-metal ionic solutions to manage gram-negative bacteria in citrus trees

Huanglongbing (HLB), a devastating disease of citrus, requires the immediate deployment of control agents to mitigate industry losses. The causative agent of HLB is the gram-negative bacteria Candidatus Liberibacter asiaticus (CLas) transmitted by the psyllid, Diaphorina citri. Recently, oxytetracycline, a common antibiotic, was approved for use to control the bacteria through tree trunk injection. Treatment has a significant effect on CLas titer within infected citrus trees in fields and potentially gives growers the ability to maintain tree productivity. However, there is the risk of resistance development through abundant use of antibiotics and so additional molecules able to control CLas within citrus trees are needed. Unfortunately, screening CLas directly is difficult as there are currently no in vitro cultures available. To screen molecules quickly and efficiently for activity, a culturable gram-negative bacteria, Agrobacterium tumefaciens, was chosen to act as a surrogate to CLas. The 96-well plate assay, determines the minimum concentration, MIC, for growth inhibition. Two nano-metal solutions (Ag, and Zn) were screened, and the lowest effective concentrations determined. Nanoparticle metals, in ionic solutions show promising activity as a treatment to suppress CLas. Results from treated CLas-infected potted citrus trees under greenhouse-conditions are presented.