The impact of Diaphorina citri vectored Candidatus Liberibacter asiaticus on citrus metabolism.

'Candidatus' Liberibacter asiaticus is associated with the devastating citrus disease Huanglongbing. It is transmitted by grafting infected material to healthy plants and by the feeding of the Asian citrus psyllid (Diaphorina citri). Previously, we demonstrated that a metabolomics approach using proton-Nuclear Magnetic Resonance spectroscopy discriminates healthy from diseased plants via grafting. The present work assessed the capability of this technology in discriminating healthy and diseased plants when the bacterium is vectored by psyllids. One-year old greenhouse-grown 'Lisbon' lemon trees were exposed to either carrier psyllids (Exposed, n = 10), or psyllids that were free of Liberibacter asiaticus (Control, n = 6). Leaf metabolites were tracked for 1 year and disease diagnosis was made using quantitative polymerase chain reaction. Overall, 31 water-soluble metabolites were quantified in leaves, including 4 sugars and 12 amino acids. Analysis via non-metric multidimensional scaling and principal components analysis revealed significant differences between the leaf metabolome of Control vs. infected trees beginning at 8 weeks post-exposure, including alterations in glucose and quinic acid concentrations. These findings provide a longitudinal overview of the metabolic effects of HLB during the early phases of disease, and confirm previous experimental work demonstrating that infection elicits changes in the leaf metabolome that enables discrimination between healthy and infected plants. Here we demonstrate that the mode of inoculation (i.e. graft- vs. psyllid-) results in a similar pathology.