First Report of Bursaphelenchus thailandae on Pinus densiflora in Korea.

Abstract

A survey of nematodes on Pinus densiflora in Namyangju City, Gyeonggi Province, Korea was conducted in 2008. Namyangju is located in an area with pine wilt caused by Bursaphelenchus xylophilus and monitoring of wilt has been conducted periodically. Nematodes were extracted from wood chips by the Baermann's funnel method and were cultured on a medium of Botrytis cinerea. During the survey, B. xylophilus and B. thailandae were detected. B. thailandae was found in 20% of the trees tested and usually was found alone without B. xylophilus. Population density of B. thailandae ranged from 8,000 to 15,000 nematodes per 100 g of wood chips. The species was identified by morphology and molecular characterization. B. thailandae was differentiated from B. xylophilus by slight swellings of the stylet knobs, protruding vulval flaps and pointed tail in females, and the male spicule with distinctive shading in the dorsal region. Morphometric data was obtained by measurements of 20 females and 10 males: female, body length = 951.3 ± 56.6 μm, a = 31.8 ± 1.9, b = 10.8 ± 0.9, c = 23.4. ± 0.8, V = 76.2 ± 0.8, stylet length = 14.5 ± 0.6 μm, length of postuterine sac = 90.3 ± 13.5 μm; male, body length = 838.0 ± 71.5 μm, a = 31.1 ± 2.1, b = 5.2 ± 0.5, c = 30.4 ± 2.7, stylet length = 13.5 ± 1.1 μm, spicules length = 16.5 ± 0.7 μm. Measurements were compared with the original description of B. thailandae reported by Braasch and Braasch-Bidasak (1), which showed that the Korean isolate was larger in most body sizes. For molecular diagnosis, the internal transcribed spacer (ITS) and D2-D3 rDNA were amplified by PCR (US/PTC-0220; Bio Rad, Hercules, CA). The sequences of ITS and D2-D3 rDNA of B. thailandae from P. densiflora showed 98 and 99% homology to those of B. thailandae from GenBank Accession Nos. AM157746 and DQ497184, respectively. B. thailandae was originally described on Pinus merkusi in Pai, North Thailand (1) while Ningbo Entry-Exit Inspection and Quarantine Bureau in China reported a detection of B. thailandae in the imported packaging wood from Hong Kong, Japan, Korea, Italy, and the United States (2). However, packaging wood is a circulating product and the establishment of B. thailandae in those countries is not confirmed. The pathogenicity of B. thailandae on coniferous trees remains to be determined. To our knowledge, this is the first report of B. thailandae on P. densiflora in a natural area in Korea.