Submitted to: BMC Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/6/2012
Publication Date: 3/20/2012
Publication URL: http://handle.nal.usda.gov/10113/60466
Citation: Islam, M., Glynn, J.M., Bai, Y., Duan, Y., Coletta-Filho, H., Kuruba, G., Civerolo, E.L., Lin, H. 2012. Multilocus microsatellite analysis of ‘Candidatus Liberibacter asiaticus’ associated with citrus Huanglongbing worldwide. BMC Microbiology. Available: http://dx.doi.org/10.1186/1471-2180-12-39. Interpretive Summary: Huanglongbing (HLB) is one of the most devastating citrus diseases worldwide. Although substantial efforts have been made toward detection of the pathogens, information regarding genetic variation and structure among worldwide populations is limited. With the recent availability of ‘Ca. L. asiaticus’(CLas) genome sequences, a panel of 7 simple sequence repeat (SSR) markers were developed and used to infer phylogenetic relationships among HLB-associated Las strains from geographically- and ecologically-diverse regions, including United States, China, India, Brazil, Cambodia, Vietnam, Taiwan, Thailand, and Japan. Genetic analyses indicate that at least three clusters of ‘Ca. L. asiaticus’ are associated with HLB worldwide. Genotypic profile analyses further revealed that the recent outbreaks of HLB in Florida citrus plantings were likely introductions from China and Brazil. Multilocus SSR genotyping system developed in this study provides improved resolution for genotyping, tracking the movement of ‘Ca. L. asiaticus’and for genetic analyses of ‘Ca. L. asiaticus’ populations.
Technical Abstract: Huanglongbing (HLB) is one of the most destructive citrus diseases worldwide. In the United States (US), HLB is typically associated with the presence of a fastidious phloem-limited bacterium named ‘Candidatus Liberibacter asiaticus’, though other Liberibacter species also have been associated with HLB in Brazil and South Africa. In North America, the pathogen is transmitted by a phloem-feeding psyllid, Diaphorina citri, and affected trees usually decline and eventually die within a few years of disease onset. While the causal agents of HLB had been putatively identified, information regarding genetic diversity, population structure and epidemiological relationships of ‘Ca. L. asiaticus’ populations from HLB-affected plants worldwide is limited. The availability of the ‘Ca. L. asiaticus’ genome sequence facilitates development of molecular markers for genetic characterization of HLB-associated bacterium. In this study, a panel of 7 simple sequence repeat (SSR) polymorphic molecular markers for ‘Ca. L. asiaticus’ was developed. Using this multilocus SSR marker system, genotypic profiles for nearly 300 ‘Ca. L. asiaticus’ strains from the US, China, India, Brazil, Cambodia, Vietnam, Taiwan, Thailand, and Japan were generated. Genetic analyses of these profiles identified three clusters of ‘Ca. L. asiaticus’ associated with HLB worldwide. Furthermore, genotypic profile analyses indicated that the recent outbreak of HLB in the southeastern US probably occurred as a result of at least two separate introductions from China and Brazil. The multilocus SSR genotyping system developed in this study provides improved resolution for genotyping, tracking the movement of strains and for assessing genetic diversity and population structure of ‘Ca. L. asiaticus’.