Submitted to: American Phytopathological Society Annual Meeting
Publication Type: Abstract Only
Publication Acceptance Date: 5/14/2008
Publication Date: 7/26/2008
Citation: Chen, J., Deng,, X., Liu,, S., Pu,, X., Li,, H., Civerolo, E.L. 2008. Detection of phytoplasma and Candidatus Liberibacter asiaticus in citrus showing Huanglongbing (yellow shoot disease) symptoms in Guangdong, P. R. China. Phytopathology 98:535.
Technical Abstract: Huanglongbing (HLB) or yellow shoot disease (ex. greening disease) is highly destructive to citrus production worldwide. HLB is currently known to be associated with Candidatus Liberibacter asiaticus in China. However, Koch’s postulates have not been fulfilled. It also remains unclear if other plant pathogens are involved. In two surveys performed in Guangdong, P. R. China in 2006 and 2007, 141 samples were collected from citrus trees showing typical symptoms of HLB from 11 different cities. PCR using phytoplasma specific primer sets fU5/rU3 nested with primer set P1/P7 identified 110 (78.0%) positive samples. A 1,785 bp amplicon was obtained with primer set P1/P7 and showed a 100% identity to three strains of Ca. Phytoplasma asteri (onion yellows (Japan), aster yellows ‘watercress’ (Hawaii), and valeriana yellows (Lithuania). Meanwhile, 89 (63.1%) samples were positive for Ca. Liberibacter asiaticus. Sixty-nine (48.9%) samples were positive to both phytoplasma and Ca. L. asiaticus. Transmission electron microscopy (TEM) showed both walled and wall-less bodies in phloem tissue of symptomative citrus. HLB phytoplasma was further demonstrated in periwinkle (Catharanthus roseus (L.) G. Don.) following transmission through dodder (Cuscuta campestris Yunck). PCR detected the same phytoplasma in the affected periwinkle, along with Ca. L. asiaticus. In addition to yellowing/mottling, the infected periwinkle showed typical symptoms of virescence and phyllody that are commonly associated with phytoplasmal diseases. TEM revealed bacteria-like organisms with pleomorphic morphology. Data from this study showed that in addition to Ca. L. asiaticus, a phytoplasma related to Ca. P. asteri was associated with citrus HLB in Guangdong.