As suggested by the historical evidence and review of the early literature related to HLB, the most ancient population of ‘Ca. L. asiaticus’ perhaps originated in India. From the 20th century onward, HLB spread through much of the citrus-growing regions of south and southeast Asia [2], the Arabian peninsula [31], East Timor and Papua New Guinea [32], and the western hemisphere (Brazil and the United States) [1]. It is difficult to precisely know when the disease entered each country and from where it was introduced. Frequent

shipment of plant materials and unlawfully importation of plants has increased the risk of disseminating exotic plant pathogens around the world. The exact pathways responsible for introducing HLB

and the Asian citrus psyllid into the United States and Brazil have not yet been determined. The genetic relationships this website of the isolates in this study, as determined from the UPGMA based on Nei’s genetic distance [22] and individual based clustering analysis by the STRUCTURE analyses, consistently identified three major genetic groups of ‘Ca. L. asiaticus’, with isolates from India included in a distinct genetic group (Figure 2 and Figure 3). The similar genetic makeup amongst most isolates from east-southeast Asia and South America (São Paulo, Brazil) support the hypothesis of the introduction of ‘Ca. L. asiaticus’ into South America from East Asia or Southeast Asia. While most isolates from Florida were clustered within a separate group, both UPGMA and STRUCTURE

analyses showed that some isolates from central Florida overlapped with east-southeast Asian and selleck Brazilian groups. The presence of two genetic groups in Florida suggests at least two introduction events are associated with the recent outbreak of HLB in Florida. Based on the history of HLB, it could be predicted that populations Amine dehydrogenase of ‘Ca. L. asiaticus’ in Florida were most likely established following the introduction of HLB-affected plant materials or ‘Ca. L. asiaticus’-carrying psyllid from Asia or other countries through human-mediated transport. The analyses in this study do not support the hypothesis of introduction of HLB into the Americas through biological materials sourced from India. Only a single isolate from India (Prakasam District, Andhra Pradesh) overlapped with the east-southeast Asian and Brazilian group (Figure 2, red). STRUCTURE analysis revealed that less-dominant clusters (Figure 2, red) in central Florida (Polk, Pasco, and Lake Counties) were observed in the same lineage (q ≥ 0.90) with east-southeast Asian and Brazilian clusters suggesting that the origin of members of this cluster in Florida might be derived from Asia or via Brazil. Moreover, some admixed (q < 0. 90) isolates between Florida and east-southeast Asia also support the hypothesis of introducing ‘Ca. L. asiaticus’ into Florida from Asia.