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Control of Huanglongbing through penicillin G trunk injection

Xiaoan Sun: Division of Plant Industry, Florida Department of Agriculture and Consumer Services (FDACS)

<div>A 2-year field trial was set up to evaluate the effect of penicillin G injection into Huanglongbing (HLB) infected citrus trees on Candidatus <em>Liberibacter asiaticus </em>(Las) titers, tree health, yield, and bacterial community profiles from within foliage and rhizosphere. Penicillin G injected into citrus trunks was detected through a bioassay and found to be rapidly but unevenly transported into citrus leaves, fruits, and roots within 24 to 48 with its concentrations declining by 72 hours. With the presence of penicillin G at a lethal concentration (>0.1 PPM) inside citrus tissues for only about seven days, Las titers in the leaves of the treated citrus trees were largely reduced. Whole genome sequencing data indicated that foliage-associated bacterial profiles did not change much and penicillin resistant genes were not detected in those bacteria in leaves where penicillin G was detected. Penicillin G was not detected in soils surrounding the roots, indicating that the antibiotic did not exit the roots. Preliminary measurements indicated increases in canopy density and fruit yield from trees treated with penicillin G. At time of harvest, penicillin G was not detected 132 days post-injection and total residue of its metabolites was less than 7 ppb in Hamlin sweet orange fruit at 132 days and less than 0.5 ppb in Valencia sweet orange fruit at 257-264 days post-injection using a LC/MS testing method. Through this trial, we believe that penicillin G treatment of HLB infected citrus through trunk injection could be utilized as an option for citrus growers in combating HLB in Florida.</div>