W.-W. Song, and
W.-Q. Qin, Coconut Research Institute, Chinese Academy of Tropical Agricultural Sciences, Wenchang 571339, Hainan Province, China; and
C.-H. Lin, Environment and Plant Protection Institute, Chinese Academy of Tropical Agricultural Sciences, Danzhou 571737, China. The project was partially funded by the Special Fund for Agro-Scientific Research in the Public Interest (20090326) and the Opening Foundation (PDCTA1002) of Hainan State Key Laboratory for the Surveillance and Control of Tropical Agricultural Products
Stem bleeding of coconut was discovered in 2009 in Hainan, China. Affected trunk areas exhibited dark discoloration and a reddish brown or rust-colored liquid bleeding from different points. Stem tissues under the lesions rotted and became brownish yellow to black. Affected plants died within 3 to 4 months after stem symptoms first appeared. Stem bleeding of coconut is known to occur in production areas worldwide. The disease was first reported in Sri Lanka (1), caused severe damage to PB-121 hybrids in Indonesia (2), and is now known to occur in many other coconut-producing countries. However, to our knowledge, this is the first report of the disease in China. A fungus was isolated from lesion margins of diseased coconut trees. Colonies on potato dextrose agar (PDA) were white, became black 1 to 2 days later, and emitted a strong, fruity aroma. The fungus produced conidia, which were cylindrical, colorless to pale brown, and 6.9 to 14.9 × 3.1 to 6.0 μm, and oval, black chlamydospores that were 7.9 to 19.4 × 4.6 to 11.0 μm. The optimum temperature for mycelial growth ranged from 25 to 35°C and it did not grow at temperatures lower than 5°C or higher than 40°C. On the basis of these characteristics, the fungus was identified as Ceratocystis paradoxa (Dade) C. Moreau (anamorph Thielaviopsis paradoxa (de Seynes) Höhn). The internal transcribed spacer (ITS) region was amplified from genomic DNA with primers ITS1 and ITS4 and the PCR products were sequenced (GenBank Accession No. JQ039332). BLAST analysis showed 99% sequence similarity with C. paradoxa (GenBank Accession No. HQ248205.1). Pathogenicity of the fungus was tested by inoculating 10, 3-year-old coconut trees of the cv. green tall at the 12-leaf stage in the field. Agar plugs (5 mm in diameter) from the periphery of 7-day-old C. paradoxa colonies grown on PDA were placed on healthy trunks, rachis, and leaves, which were either wounded or unwounded. Wounds were made with a sterilized cork borer. Sites of the inoculations were wrapped with plastic tape to prevent desiccation; the experiment was repeated three times. Controls received plain PDA discs. Two weeks after inoculation, characteristic rusty brown lesions appeared only on wounded plants that were inoculated with the fungus. A brownish liquid oozed from the points of inoculation. Controls did not show signs of disease development. C. paradoxa was reisolated from the diseased tissues. Infection occurred on wounded sites only, suggesting that wounds may be required for infection. To prevent stem bleeding of coconut trees by C. paradoxa, vigilant cultural practices must be maintained to avoid causing wounds on the trees.
References: (1) S. A. Alfieri. Plant Pathol. Circular No. 53. Florida Department of Agriculture Division of Plant Industry, 1967. (2) D. R. N. Warwick and E. E. M. Passos. Trop. Plant Pathol. 34:175, 2009.