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First Report of a Group 16SrI-B Phytoplasma Associated with Gardenia jasminoides in China

Gardenia jasminoides J. Ellis, (also known as common gardenia, cape jasmine, or cape jessamine) is a fragrant flowering evergreen tropical plant, a favorite in gardens worldwide. G. jasminoides were found with small, seriously yellowed leaves, stunted growth, and witches'-broom in a green belt on the Southwest University campus in October 2011. The incidence was lower than 2%. In another green belt, G. jasminoides with only slightly yellowing leaves were found. The incidence was about 5%. Five months later, most seriously yellowed leaves withered. However, no withered leaf was observed among the slightly yellowing leaves. Leaf samples from each symptomatic plant, together with asymptomatic plants from the same belt, were collected for total DNA extraction using a modified cetyltrimethylammoniumbromide method (1). The resulting DNA extracts were analyzed by a nested PCR assay using the phytoplasma 16S rRNA gene primer pairs R16mF2/R16mR1 followed by R16F2n/R16R2 (2). DNA fragments of 1.2 kb that corresponded to 16S rDNA were amplified only from the DNA samples of the five plants with the symptoms mentioned above. The purified nested PCR products were cloned in pGEM-T Easy Vector (Promega) and then sequenced. The resulting 16S rDNA sequences were found to be identical (GenBank Accession No. JQ675713). The consensus sequence was analyzed by the iPhyClassifier online tool (http://plantpathology.ba.ars.usda.gov/cgi-bin/resource/iphyclassifier.cgi) and found to share 99.4% similarity with the 16S rDNA sequence of the ‘Candidatus Phytoplasma asteris’ reference strain (GenBank Accession No. M30790) that belongs to the 16SrI-B subgroup (3). The virtual RFLP pattern of the G. jasminoides phytoplasma 16S rDNA gene sequence showed maximum similarity to the reference pattern of NC005303 (similarity coefficient of 1.0). The phylogenetic tree based on the 16S rDNA sequences of phytoplasmas belonging to group 16SrI and other distinct phytoplasma groups also showed that our sequences clustered with members of subgroup 16SrI-B. Subsequently, the presence of the phytoplasmas in symptomatic plants was also confirmed by transmission electron microscopy. Taken together, the phytoplasma was classified as a member of subgroup 16SrI-B. To our knowledge, this is the first report of a subgroup 16SrI-B phytoplasma associated with diseased G. jasminoides in China. G. jasminoides yellowing is often considered to result from nutrient deficiency (especially iron compounds). However, our findings showed that a phytoplasma can cause G. jasminoides yellowing, which should be considered in the control of leaves yellowing.

References: (1) E. Angelini et al. Vitis 40:79, 2001. (2) D. E. Gundersen and I.-M. Lee. Phytopathol. Mediterr. 35:144, 1996. (3) Y. Zhao, et al. Int. J. Syst. Evol. Microbiol. 59:2582, 2009.