Q. H. Tang and F. Y. Yu, Coconut Research Institute, Chinese Academy of Tropical Agricultural Sciences, Wenchang, Hainan 571339 P. R. China; S. Q. Zhang, Institute of Tropical Bioscience and Biotechnology, CATAS, Haikou, Hainan 571101 P. R. China; and X. Q. Niu, H. Zhu, W. W. Song, C. W. Han, D. Y. Wu, and W. Q. Qin, Coconut Research Institute, Chinese Academy of Tropical Agricultural Sciences, Wenchang, Hainan 571339 P. R. China. The project was funded by National Nonprofit Institute Research Grant of CATAS-ITBB (No. 1630052012016) and Natural Science Foundation of Hainan Province (No. 312041).
In May 2009, a severe bacterial disease of arecanut (Areca catechu L.) with an incidence of 100% was observed in a plantation of about 8,400 plants in Wenchang City, Hainan Province, China (19°47.171′ N, 110°54.335′ E). Symptoms consisted of small circular to elongated brown lesions, ranging from 1 to 105 mm in length and 1 to 21 mm in width, surrounded by yellow halos. White colonies, without fluorescent or diffusible pigments, were consistently recovered on King's B Medium plates from lesions surface-sterilized in 70% ethyl alcohol for 1 min. All isolates were gram-negative and each had a single, polar, sheathed flagellum. Isolates were identified as a Burkholderia sp. based on physiological and biochemical tests: oxidase and catalase positive, negative for arginine dihydrolase, gelatin hydrolysis and starch hydrolysis, and negative for acid production from levan (1,3). Sequences (approx. 1,400 bp each) of the 16S rRNA gene amplified from four isolates using primer pair 27F/1492R (2) (GenBank Accession Nos. JX415481, JX415479, JX415482, and JX415483) shared 99% sequence identity with that of Burkholderia andropogonis strain 6369 (DQ786951). Representative isolates Y11 (China General Microbiological Culture Collection Center No. CGMCC 1.12337), Y30 (CGMCC 1.12338), W15, and W20 were compared with B. andropogonis strain NCPPB No. 1012 and all caused a hypersensitive reaction on leaves of Nicotiana benthamiana. Isolate pathogenicity was tested twice with a total of three replications per isolate. Two young leaves each of 2-year-old arecanut plants were infiltrated with a bacterial suspension of 108 CFU/ml, then covered individually with plastic bags for 48 h, and incubated at 100% relative humidity with 16 h of daylight at 25°C by day and 8 h of darkness at 20°C by night. After 7 days, small water-soaked spots with yellow halos were observed and 60 days after inoculation, lesions developed similar to those caused by B. andropogonis in the field. Koch's postulates were fulfilled by reisolating bacteria from typical lesions on inoculated plants. These bacteria were identical to inoculated strains in colony morphology and sequences of the 16S ribosomal RNA gene. To our knowledge, this is the first report of B. andropogonis infection on betel in Hainan Province, mainland China. This disease was first reported in Taiwan, a province of China. Conditions of high humidity and high temperature support disease outbreaks and infection can result in severe economic losses. In 2012, this disease also appeared on a number of plantations located in other counties. As betel is, economically, the second most important crop in Hainan Province, measures should be required to control this disease, especially in typhoon seasons.
References: (1) S. H. Hseu et al. Plant Pathol. Bull. 16:131, 2007. (2) D. J. Lane. In: E. Stackebrandt, et al. Nucleic acid techniques in bacterial systematics. John Wiley & Sons, Chichester, United Kingdom, pp. 115-175, 1991. (3) X. Li and S. H. De Boer. Plant Dis. 89:1132. 2005.