Metabolic Mechanisms of Host Species Against Citrus Huanglongbing (Greening Disease)

AbstractHuanglongbing (HLB), previously known as citrus greening disease, is a devastating disease caused by gram negative, phloem-limited, fastidious bacteria Candidatus Liberibacter spp. HLB exists in nearly all commercially cultivated citrus, causing losses to growers by affecting tree vigor, production, fruit development, and quality. Recently, some promising HLB-tolerant germplasm has been identified, and showed particularly high concentration of metabolites, such as flavone, flavanone, aldehyde, and monoterpene. This review focuses on the citrus metabolic response against the HLB and we have summarized a comprehensive metabolic pathway that is activated in response to HLB. The antibacterial role of these metabolites, which were high in the HLB tolerant varieties are discussed. Generally, most of the amino acids, flavonoids, terpenes, and volatile compounds were significantly higher, even hundreds times of increase, in HLB-tolerant varieties. We also summarized the secondary metabolites, which were d...