Huanglongbing in Cuban Citriculture

摘要

Huanglongbing is the most devastating disease of citrus in the world at present. In 2007, plants from different citrus varieties with blotchymottled leaves and fruits showing typical HLB-like symptoms were observed in urban areas of Havana, Cuba. The presence of Candidatus Liberibacter bacteria was corroborated by PCR amplification and transmission electron microscopy of symptomatic leaves collected throughout the country. Encapsulated bacterial cells of varying length containing inner membranes and a granular material were observed in the phloem sieve tubes that are similar to those described for Liberibacter species. Characteristic PCR products with a size corresponding to that expected for Candidatus Liberibacter asiaticus were obtained in 18 out of 20 samples collected, by duplex PCR amplification using A2/J5/GB1/GB3 primers. A typical restriction pattern of two fragments was also shown after Xba I digestion of PCR products primed with OI1/OA1/OI2c. Fragments from the/p/KAJL-rpoBC operon were cloned, sequenced and compared to those published in the GenBank. BLAST searches yielded the highest scores with Ca. L. asiaticus sequences, with identities ranging from 99% to 100%. Ca. L. asiaticus was also detected with PCR primer set A2/J5 in Diaphorina citri adults collected from symptomatic citrus plants infected with the bacteria. Based upon the HLB situation in Cuban citrus areas, a management program has been established which includes periodic surveys, eradication of infected plants, and control of Diaphorina citri using insecticides and, whenever possible, use of parasitic hymenoptera such as Tamarixia radiata as a biological control.