Abstract: Citrus Huanglongbing is a devastating disease in the global citrus industry, primarily caused by bacterium of the genus Candidatus Liberibacter, which comprises three species: asiaticus (CLas), africanus (CLaf) and americanus (CLam). Among them, CLas is the predominant species in China. This study conducted phage and transposon gene sequence differential analyses on 183 citrus leaf samples carrying CLas from Hunan Province, Guangxi Zhuang Autonomous Region, Jiangxi and Guangdong Province, and additionally performed outer membrane protein (OMP) gene sequence differential analysis on 19 samples from four cities in Hunan Province. It was found that CLas had three transposon combinations and seven phage combinations. The most frequent CLas population in the four regions was characterized by the absence of the MCLas-A type transposon and the presence of a single T2 phage, with a discrimination index (DI) of 0.534 0. Cluster analysis based on phage and transposon types divided all samples into three clusters at a genetic distance of 0.15: Ji’an and Ganzhou in Jiangxi formed the first cluster; Chenzhou and Yongzhou in Hunan clustered together and branched with Zhaoqing of Guangdong, forming the second cluster; samples from other countries such as Indonesia, Vietnam, Japan, and Thailand formed the third cluster. The number of mutated nucleotide sites in the OMP gene of each sample ranged from 0 to 4, with a total of 18 different nucleotide mutation sites, indicating a high genetic diversity in OMP. The clustering results showed that most domestic CLas samples clustered together, while samples from Indonesia, Vietnam, Japan, and Thailand formed another cluster. This pattern clearly indicates a certain degree of genetic isolation among different geographical populations, providing critical genetic evidence for understanding the population evolution and transmission routes of the CLas.
Keywords: Candidatus Liberibacter asiaticus; outer membrane protein gene; bacteriophage transposon; genetic diversity; population structure analysis
（Acta Laser Biology Sinica, 2026, 35(3): 233-240）