Abstract: A multiplex RT-PCR was successfully established to simultaneously detect Citrus Huanglongbing pathogen (Candidatus Liberibacter asiaticus, HLB) , Citrus exocortis viroid (CEVd) and Citrus tristeza virus (CTV). Using three sets of specific primers designed according to the converted sequences of these three
pathogens respectively, expected fragments of 1 160 bp (HLB) , 371 bp (CEVd) and 273 bp (CTV) were successfully amplified by thismultiplex RT-PCR systerm. To optimize the multiplex RT-PCR, the concentration of primers and annealing temperature were repeatedly tried. Final results showed that a multiplex RT-PCR system to simultaneously detect HLB, CEVd and CTV was firstly established successfully. Sensibility test showed: it could detect out HLB, CEVd in 10 pg, and CTV in 1 pg total RNA respectively. To confirm the utilization of the multip lex RT-PCR system, 37 samples collected from field were tested. The results showed:two or three pathogensmix2infection was in existence in fields.

Key words: Citrus, Multiplex RT-PCR, Huanglongbing, Citrus exocortis viroid, Citrus tristeza virus, Detection