A metabolomics assay to diagnose citrus Huanglongbing (HLB) disease and to aide assessment of treatments to prevent or cure infection
Mitchell M. McCartney, Michael Eze, Eva Borras, Michael Edenfield, Ozgur Batuman, Denise C. Manker, John V. da Graça, Susan E. Ebeler, Cristina Davis- Plant Science
- Agronomy and Crop Science
Citrus greening disease or huanglonbing (HLB) has devastated citrus crops globally in recent years. The causal bacterium, Candidatus Liberibacter asiaticus, presents a sampling issue for qPCR diagnostics and results in a high false negative rate. In this work, we compared six metabolomics assays to identify HLB-infected citrus trees from extracted leaf tissue from 30 control and 30 HLB-infected trees. A liquid chromatography-mass spectrometry (LC-MS) based assay was most accurate. A final partial least squares-discriminant analysis (PLS-DA) model was trained and validated on 690 leaf samples with corresponding qPCR measures from three citrus varieties (Rio Red grapefruit, Hamlin sweet orange and Valencia sweet orange) from orchards in Florida and Texas. Trees were naturally infected with HLB transmitted by the insect vector Diaphorina citri. In a randomized validation set, the assay was 99.9% accurate to classify diseased from non-diseased samples. This model was applied to samples from trees receiving plant defense inducer compounds (PDIs) or biological treatments (BLXs) to prevent or cure HLB infection. From two trials, HLB-related metabolite abundances and PLS-DA scores were tracked longitudinally and compared to control trees. We demonstrate how our assay can assess tree health and efficacy of HLB treatments, concluding no trialed treatment was efficacious.