Diversity of Candidatus Liberibacter Species Associated with Huanglongbing-Like Symptoms in Rutaceous Plants

Abstract

Diversity of “Candidatus Liberibacter” species associated with Huanglongbing (HLB)-like symptoms in rutaceous plants was investigated to elucidate pathogen variation, distribution, and potential epidemiological significance. Field surveys were conducted in citrus and related Rutaceae exhibiting characteristic symptoms including leaf mottling, vein yellowing, shoot dieback, and fruit deformation. Symptomatic leaf samples were collected and subjected to DNA extraction followed by PCR amplification targeting 16S rRNA and ribosomal protein gene regions for molecular detection. Sequencing and phylogenetic analyses revealed the presence of multiple “Candidatus Liberibacter” lineages, indicating heterogeneous infection patterns across sampled orchards. The detected variants showed clustering with known HLB-associated species, including “Ca. L. asiaticus” and related strains, suggesting complex pathogen diversity within rutaceous hosts. Differences in distribution were observed across host species and geographic locations, reflecting possible vector-mediated spread and localized adaptation. Mixed infections were also detected in certain samples, indicating co-occurrence of multiple strains within individual plants. The study highlights the epidemiological complexity of HLB-like diseases and emphasizes the need for precise molecular diagnostics to differentiate closely related Liberibacter species. These findings contribute to a better understanding of pathogen diversity in citrus systems and support the development of improved surveillance and integrated disease management strategies targeting HLB in rutaceous crops.