Multi-Locus Sequence Analysis Reveals the Genetic Diversity and Population Differentiation of Candidatus Liberibacter Asiaticus in China

Abstract

Huanglongbing (HLB) is a devastating citrus disease caused by Candidatus Liberibacter asiaticus (CLas). Since its initial outbreak in Guangdong Province, China, it has spread to 10 provinces and caused significant economic losses. Hence, assessing CLas genetic diversity and demographic history is crucial for HLB epidemic prevention and control. In this study, we collected 500 leaf samples of CLas-infected plants from 10 provinces. We performed multi-loci sequence analysis on four gene fragments (omp, DnaA, GroEL, and SDE1) to explore the genetic differentiation and diversity of CLas in China. Our results indicated low nucleotide diversity (0.00005 ± 0.00001) in CLas, with the absence of significant systematic geographic structure in its distribution. Molecular variance analysis revealed predominant (81.7%) genetic variations within the population, with a minor variation (18.3%) occurring between populations as well as Yunnan provinces. In the Fujian population, significant gene exchange occurred with the other nine populations. Significant negative values in Tajima’s D and Fu’s FS neutrality tests indicated historical population expansions. The nucleotide mismatch distribution curve exhibits a single peak pattern, further supporting the expansion events. Our findings hold potential for advancing epidemiological research and providing suggestions for effective strategies to mitigate the spread of CLas and control HLB.