Infection of wampee and lemon by the Citrus Huanglongbing pathogen (Candidatus Liberibacter asiaticus) in China

Single-step and nested polymerase chain reactions (PCR) were used to determine the presence of Candidatus Liberibacter asiaticus, the phloem-limited bacterial pathogen of Huanglongbing (HLB), in leaves of wampee [Clausena lansium (Lour.) Skeels], lemon [Citrus limon (L.) Burm.] and several other citrus species. Specific PCR products were obtained when single-step PCR and nested PCR were used to analyze wampee and lemon samples with or without visible HLB symptoms. Nested-PCR was found to be more accurate than single-step PCR with a sensitivity of about 104 times higher. The amount of bacterial DNA was positively correlated with HLB symptoms in the leaves. Amplicons from single-step PCR and those from nested PCR showed 100% and 99% identity, respectively, with sequences of the rplKAJL-rpoBC gene cluster of Ca. Liberibacter asiaticus. This pathogen is therefore able to infect wampee and lemon, in the leaves of which it can be readily detected by PCR. This is the first report of infections by Ca. L. asiaticus in wampee.