Analysis of Differential Metabolites in Citrus Leaves Infected with Huanglongbing and Screening of Biomarkers for Early Detection

Huanglongbing (HLB), a destructive citrus disease caused by Candidatus Liberibacter asiaticus (CLas), cannot be efficiently diagnosed at the early stage via conventional detection methods. Most current metabolomic studies on citrus HLB rely solely on the LC-MS platform and mainly focus on sweet orange, while integrated dual-platform metabolomic research targeting Orah mandarin, the dominant cultivated citrus variety, remains limited. In the present study, GC-MS and LC-MS were combined for the first time, alongside multivariate statistical analysis and pathway enrichment analysis, to systematically characterize metabolomic differences between healthy and HLB-infected Orah mandarin leaves. Suspected citrus leaf samples were collected from two major citrus-producing regions in Guangxi and further confirmed by qPCR detection. A large number of differentially accumulated metabolites were identified, which were primarily enriched in carbohydrate metabolism and amino acid metabolism pathways. Several candidate biomarkers applicable for early HLB diagnosis were also screened out. This study provides reliable scientific evidence and a theoretical foundation for elucidating the pathogenic mechanism of HLB and establishing field-based early diagnosis techniques.