Journal of Citrus Pathology

It will be recalled how the notions of “heat-sensitive/heat-tolerant HLB” and “African HLB/Asian HLB” were developed. These notions benefited from the possibility to confirm, for the first time, the non-specific HLB symptoms by reliable laboratory techniques: detection of the HLB-associated bacterium by transmission electron microscopy from 1970 onwards to DNA-hybridization and PCR of the liberibacters in the 1990s. With these tools, the early history of citrus HLB in the many countries surveyed could be more precisely described. This presentation also shows or proposes why: (i) African HLB is heat-sensitive and Asian HLB, heat-tolerant; (ii) only one of the seven known liberibacters, namely Candidatus Liberibacter asiaticus (Las), is heat-tolerant, Candidatus Liberibacter africanus (Laf) being a heat-sensitive liberibacter; (iii) African HLB is native to Africa, and Asian HLB is native to Asia; (iv)  “Continental Drift” supports astonishingly well the presence of Laf in Africa and  that of Las in Asia; presence of Las in the Americas is the result of incursions; (v) HLB  is not native to the Arabian Peninsula, but is the result of African and Asian HLB incursions into the peninsula; vi) recent presence of Las in Ethiopia is also the result of an incursion; vii) Candidatus Liberibacter americanus (Lam) in South America is the result of an incursion too; viii) while Laf and Las are of Gondwanan origin, Candidatus Liberibacter europaeus