|Abdullah, Siti Nor Akmar|
Submitted to: International Journal of Systematic and Evolutionary Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/17/2012
Publication Date: 2/1/2013
Citation: Nejat, N., Vadamalai, G., Davis, R.E., Harrison, N.A., Sijam, K., Dickinson, M., Abdullah, S., Zhao, Y. 2012. Candidatus Phytoplasma malaysianum, a novel taxon associated with virescence and phyllody of Madagascar periwinkle (Catharanthus roseus). International Journal of Systematic and Evolutionary Microbiology. 63:540-548. Interpretive Summary: Phytoplasmas are a large group of small bacteria that lack a cell wall. These bacteria occupy nutrition-transporting vessels of affected plants and, as a result, cause poor growth, commodity loss, reduced product quality, and even death of the host plants. Recently, new phytoplasmas associated with emerging diseases in diverse plants including periwinkle, coconut palm, and oil palm trees were identified in Malaysia. In the present study, we conducted gene ancestry and computer-assisted DNA fingerprint analyses to determine the genetic relationship between these new phytoplasmas and previously known phytoplasmas. We presented evidence to demonstrate that these Malaysian phytoplasmas possess distinct genetic features and represent a new species. We named this species ‘Candidatus Phytoplasma malaysianum’. We have also found molecular markers that can be used for quick identification of phytoplasmas belonging to this species. Furthermore, we erected a new phytoplasma group to accommodate diverse phytoplasma strains that share similar DNA fingerprints. This report will be of interest to diagnostics laboratories, research scientists and extension personnel who are concerned with phytoplasma disease management. The information is also important to international quarantine agencies for implementation of new quarantine regulations, since the new phytoplasma species determined in the present study has been found only in Asia so far.
Technical Abstract: This study addressed the taxonomic position and group classification of a phytoplasma responsible for virescence and phyllody symptoms in naturally diseased Madagascar periwinkle plants in western Malaysia. Unique regions in the 16S rRNA gene from the Malaysian periwinkle virescence (MaPV) phytoplasma distinguished the phytoplasma from all previously described ‘Candidatus Phytoplasma’ species. Pairwise sequence similarity scores, calculated through alignment of full-length 16S rRNA gene sequences, revealed that the MaPV phytoplasma 16S rDNA shared 96.5% or less sequence similarity with that of previously described ‘Ca. Phytoplasma’ species, justifying the recognition of the MaPV phytoplasma as a reference strain of a novel taxon, ‘Candidatus Phytoplasma malaysianum’. The 16S rDNA F2nR2 fragment from the MaPV phytoplasma exhibited a distinct restriction fragment length polymorphism (RFLP) profile and the pattern similarity coefficient values were lower than 0.85 with representative phytoplasmas classified in any of the 31 previously delineated 16Sr groups; therefore, the MaPV phytoplasma was designated member of a new 16Sr group, 16SrXXXII. Phytoplasmas affiliated with this novel taxon and new group included diverse strains infecting periwinkle, coconut palm, and oil palm in Malaysia. Three phytoplasmas were characterized as representatives of three distinct subgroups, 16SrXXXII-A, 16SrXXXII-B, and 16SrXXXII-C, respectively.