Bacterial diseases in plants can decimate groves and plantations by rapidly reducing production yields. An endemic infection can have devastating economic consequences at large, as seen in Florida due to Huanglongbing (HLB) – or citrus greening disease. HLB is a phloem-restricted bacterial infection spread by Asian Citrus Psyllids (ACPs) as they feed from the leaves phloem. The presence of the bacteria in the plant can affect the natural delivery of nutrients by clogging the vascular system, leading to early fruit drop with poor juice quality. With decimated groves and low fruit yield, the multibillion dollar citrus industry is facing severe economic hardship.
All disease management methods considered to date have failed to stop the progression of the disease or to improve the health of infected trees. Hence, based on their previous success in the treatment of fireblight disease in apple and pear trees, antibiotics including streptomycin and oxytetracycline combined with adjuvants are currently being evaluated. Their diffusion and translocation in Valencia Orange trees (Citrus sinensis) is the focus on this work. To model the processes, single leaf and seedling assays and whole plant spray simulations have been designed to quantify the uptake and translocation rate. We present results showing that Raman spectroscopy can be used to evaluate the presence of Streptomycin based on its fingerprint in the 900-1600 cm-1 range. We discuss important considerations including the protocols developed to ensure that surface residues are removed during the cleaning process to avoid interferences with the measurements on leaf sections. Finally, we consider the time evolution of the diffusion and translocation processes in the presence of adjuvants in the treatment. Overall, our results present a multi-scale approach to map pesticide-plant interactions at the tissue level.