Submitted to: Plant Health Progress
Publication Type: Peer reviewed journal
Publication Acceptance Date: 12/20/2006
Publication Date: 12/20/2006
Citation: Deng, X., Chen, J., Zhou, G., Li, H., Civerolo, E.L. 2006. Identification of Candidatus Liberibacter asiaticus from Wampee (Clausena lansium Skeels) in Guangdong Province, P. R. China. D01:10.1094/PHP-2007-0419-01-BR Interpretive Summary: This report is one of our efforts to determine sources of the citrus Huanglongbing (HLB) pathogen, Candidatus Liberibacter spp. Wampee (Clausena lansium) is a small tree native to southern China where HLB originated and is also grown in Hawaii, Florida, and California. This citrus family member has long been suspected to have HLB because it can exhibit “yellow shoot” symptoms and could serve as a primary source of HLB pathogen for citrus. Using a nested-polymerase chain reaction technique, we demonstrated the presence of the HLB pathogen in wampee leaves showing yellowing/mottling symptoms in Guangdong Province, P. R. China. Results from this study indicate that wampee should be considered as a source of the HLB pathogen in efforts to control the disease in citrus.
Technical Abstract: Wampee (Clausena lansium Skeels) is native to, and commonly cultivated in, southern China and southeast Asia. Like other members of Rutaceae, wampee has long been suspected to have low level of “yellow shoot” symptoms or Huanglongbing (HLB). The importance of wampee HLB is probably its potential to serve as a source of inoculum of the HLB pathogen, Candiatus Liberibacter asiaticus for susceptible citrus crops. However, the presence of Ca. L. asiaticus in wampee has not been confirmed. In August of 2006, we identified two wampee trees showing “yellow shoots” symptoms adjacent to a mandarin orchard with HLB in Luoding City, Guangdong province, People’s Republic of China. Leaf symptoms ranged from mottling to yellowing. Symptomatic leaves were collected and DNA was extracted. DNA samples were assayed by nested-PCR. The general bacterial 16S rDNA primer set fDl/rD1 (AGA GTT TGA TCC TGG CTC AG / AAG GAG GTG ATC CAG CC) was used for the outer round amplification for ten cycles. One µl of the amplicon was then used for inner round amplification using the same procedure but 35 cycles. The inner primer set was OI1/OI2c (GCG CGT ATG CAA TAC GAG CGG CA / GCC TCG CGA CTT CGC AAC CCA T ) that is specific to Ca. L. asiaticus. A 1,160 bp amplicon was obtained from symptomatic but not asymptomatic samples. The PCR amplicon was digested by XbaI into two fragments of 520bp and 640 bp, suggesting the presence of Ca. L. asiaticus. Sequence of amplicons were further determined to be 1,167 bp and shared >98% similarity to sequences of Ca. L. asiaticus in the current GenBank database. To our knowledge, this is the first report of molecular identification of Ca. L. asiaticus associated with wampee showing leaf mottling / yellowing symptoms in Guangdong Province of P. R. China.