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First Report of Leaf Spot of Tea Oil Camellia (Camellia oleifera) Caused by Lasiodiplodia theobromae in China

Tea oil camellia (Camellia oleifera Abel.), one of the most famous woody oil plants, is distributed and cultivated widely in central and southern China for its strong adaptability. In September 2013, tea oil camellia plants with severe leaf spots were observed in commercial production fields located in Wenchang, Hainan Province. Spots were initially chlorotic, became necrotic and black with a chlorotic halo, developing to cover the entire width of the leaves, and leading to leaf death. Isolations were performed by excising pieces of symptomatic leaves from the lesion margin, surface sterilized with 90% ethanol and 0.6% sodium hypochlorite, and then placed them on potato dextrose agar (PDA). Plates were incubated in a sterile chamber at 26 ± 2°C for 2 days. A fungus was consistently isolated on PDA from all 23 diseased leaf samples. Pure cultures were obtained by monosporic culture technique. After 2 to 3 days of incubation at 26 ± 2°C with a 12-h photoperiod, the fungus initially produced white colonies with dense aerial mycelia, which later turned black (6 to 7 days). The mycelium was fast spreading, branched, and septate. Pycnidia were black, globose, ostiolate, and produced in stroma on the medium surface after 28 days at the same culture conditions as above. Conidia were initially unicellular, subovoid, hyaline, thick-walled with granular content, and 19.8 to 28.9 × 11.5 to 15.7 μm (avg. 25.1 × 13.5 μm). Mature conidia were one-septate and dark brown with longitudinal striations. These observed morphological features suggested that the fungus possessed the same characteristics as previously described for Lasiodiplodia theobromae (Pat.) Griffon & Maubl (syn = Botryodiplodia theobromae) (2). For molecular identification, the ITS1-5.8S-ITS2 region and fragments of the β-tubulin and elongation factor 1-alpha (EF1-α) genes were sequenced and BLASTn searches done in GenBank. Accession numbers of gene sequences submitted to GenBank were KF811055 for ITS region; KJ639047 for β-tubulin; and KJ639048 for EF1-α. For all genes used, sequences were 99 to 100% identical to reference isolate CBS164.96 of L. theobromae reported in GenBank (NR_111174, EU673110, and AY640258). Hence, both morphological and molecular characteristics confirmed the fungus as L. theobromae. To confirm fungal pathogenicity, ten 1-year-old healthy plants of C. oleifera were inoculated with the fungus. Mycelial plugs (5 mm) taken from a 7-day-old colony growing on PDA were deposited on wounds with a sterilized knife on leaves and covered with moist cotton. Ten additional control plants were treated similarly but with sterile PDA plugs. Plants were maintained in a moist chamber at 26 ± 2°C for 3 days and then in a greenhouse at 25°C and 40% relative humidity. All the inoculated plants produced typical leaf spot symptoms 3 weeks after inoculation. The fungus was consistently re-isolated from all inoculated plants. Control plants did not show any symptoms. L. theobromae has been reported to cause cankers and dieback in a wide range of hosts and is common in tropical and subtropical regions of the world (1,2), but not previously reported causing disease on C. oleifera. To our knowledge, this is the first report worldwide of leaf spot of C. oleifera caused by L. theobromae.

References: (1) S. Mohali et al. For. Pathol. 35:385, 2005. (2) E. Punithalingam. Page 519 in: CMI Descriptions of Pathogenic Fungi and Bacteria. Commonwealth Mycological Institute, Kew, Surrey, UK, 1976.