Mayfield A E, Smith J A, Hughes M, Dreaden T J
Florida Department of Agriculture and Consumer Services, Division of Forestry, Gainesville 32608.
School of Forest Resources and Conservation, University of Florida, Gainesville 32611.
Plant Dis. 2008 Jun;92(6):976. doi: 10.1094/PDIS-92-6-0976A.
Laurel wilt is a vascular disease of redbay (Persea borbonia (L.) Spreng.) and other plants in the family Lauraceae in the southeastern United States. It is caused by a fungus (Raffaelea sp.) that is vectored by a non-native insect of Asian origin, the redbay ambrosia beetle (Xyleborus glabratus Eichhoff) (1). Since the initial detection of the redbay ambrosia beetle near Savannah, GA in 2002, laurel wilt has caused widespread mortality of redbay in Georgia, South Carolina, and Florida (1). In September 2007, an avocado (Persea americana Mill.) tree planted approximately 10 years earlier in a residential neighborhood in Jacksonville, FL was discovered to be infected with laurel wilt. The crown was in various stages of decline, including upper branches that were dead and leafless, those with wilted and drooping foliage, and those with healthy foliage. Removal of bark from wilted branch sections revealed black-to-brown streaks of discoloration in the sapwood and a few ambrosia beetle holes from which the discoloration extended into the adjacent wood. A Raffaelea sp. was isolated from discolored wood samples by surface sterilizing wood chips by submersion in a 5% sodium hypochlorite solution for 30 s and plating them on cycloheximide streptomycin malt agar (2). Small subunit (18S) sequences from the rDNA were amplified by PCR and sequenced with primers NS1 and NS4 (3). BLASTn searches revealed homology to Raffaelea sp. C2203 (GenBank Accession No. EU123076, 100% similarity, e-value of 0.0, and a total score of 1,886), which is known to be the causal agent of laurel wilt (1). The small-subunit rDNA sequence for this isolate has been deposited into GenBank and has been assigned accession No. EU257806. Pathogenicity of the laurel wilt pathogen on Persea spp. in growth chamber trials has been previously demonstrated (1). Laurel wilt is of concern to the commercial avocado industry and is a potential threat to the Lauraceae elsewhere in the Americas. References: (1) S. W. Fraedrich et al. Plant Dis. 92:215, 2008. (2) T. C. Harrington. Mycologia 73:1123, 1981. (3) T. J. White et al. Page 315 in: PCR Protocols, a Guide to Methods and Applications. M. A. Innis et al., eds. Academic Press, San Diego, CA, 1990.
月桂枯萎病是美国东南部红月桂（Persea borbonia (L.) Spreng.）以及樟科其他植物的一种维管束病害。它由一种真菌（Raffaelea sp.）引起，这种真菌由一种原产于亚洲的非本地昆虫——红月桂食菌小蠹（Xyleborus glabratus Eichhoff）传播（1）。自2002年在佐治亚州萨凡纳附近首次发现红月桂食菌小蠹以来，月桂枯萎病已导致佐治亚州、南卡罗来纳州和佛罗里达州的红月桂大量死亡（1）。2007年9月，在佛罗里达州杰克逊维尔一个居民区种植了约10年的一棵鳄梨树（Persea americana Mill.）被发现感染了月桂枯萎病。树冠处于不同程度的衰退阶段，包括上部枝条枯死且无叶、叶片枯萎下垂以及叶片健康的枝条。从枯萎的枝条切段剥去树皮后，边材出现了从黑色到棕色的变色条纹，还有一些食菌小蠹的虫孔，变色从这些虫孔延伸到相邻的木材中。通过将木片浸入5%次氯酸钠溶液中表面消毒30秒，然后将其接种在放线菌酮链霉素麦芽琼脂上，从变色的木材样本中分离出了一种Raffaelea sp.（2）。通过PCR扩增rDNA的小亚基（18S）序列，并用引物NS1和NS4进行测序（3）。BLASTn搜索显示与Raffaelea sp. C2203（GenBank登录号EU123076，相似度100%，e值为0.0，总分1886）具有同源性，已知该菌株是月桂枯萎病的病原体（1）。该分离株的小亚基rDNA序列已存入GenBank，登录号为EU257806。此前已在生长室试验中证明月桂枯萎病病原体对鳄梨属植物具有致病性（1）。月桂枯萎病受到商业鳄梨产业的关注，并且对美洲其他地区的樟科植物构成潜在威胁。参考文献：（1）S. W. Fraedrich等人，《植物病害》92:215，2008年。（2）T. C. Harrington，《真菌学》73:1123，1981年。（3）T. J. White等人，载于《PCR协议：方法与应用指南》第315页。M. A. Innis等人编著。学术出版社，加利福尼亚州圣地亚哥，1990年。
