Institute of Forest Protection, College of Forest Resources and Environment, Nanjing Forestry University, Nanjing, China.
Int J Biol Sci. 2013;9(1):34-44. doi: 10.7150/ijbs.5071. Epub 2012 Dec 19.
Pine wilt disease (PWD) caused by the pine wood nematode (PWN), Bursaphelenchus xylophilus, is one of the most devastating diseases of Pinus spp. The PWN was therefore listed as one of the most dangerous forest pests in China meriting quarantine. Virulence of the PWN is closely linked with the spread of PWD. However, main factors responsible for the virulence of PWNs are still unclear. Recently epiphytic bacteria carried by PWNs have drawn much attention. But little is known about the relationship between endophytic bacteria and virulence of B. xylophilus. In this research, virulence of ten strains of B. xylophilus from different geographical areas in six provinces of China and four pine species were tested with 2-year-old seedlings of Pinus thunbergii. Endophytic bacteria were isolated from PWNs with different virulence to investigate the relationship between the bacteria and PWN virulence. Meanwhile, the carbon metabolism of endophytic bacteria from highly and low virulent B. xylophilus was analyzed using Biolog plates (ECO). The results indicated that ten strains of PWNs showed a wide range of virulence. Simultaneously, endophytic bacteria were isolated from 90% of the B. xylophilus strains. The dominant endophytic bacteria in the nematodes were identified as species of Stenotrophomonas, Achromobacter, Ewingella, Leifsonia, Rhizobium, and Pseudomonas using molecular and biochemical methods. Moreover, S. maltophilia, and A. xylosoxidans subsp. xylosoxidans were the predominant strains. Most of the strains (80%) from P. massoniana contained either S. maltophilia, A. xylosoxidans, or both species. There was a difference between the abilities of the endophytic bacteria to utilize carbon sources. Endophytic bacteria from highly virulent B. xylophilus had a relatively high utilization rate of carbohydrate and carboxylic acids, while bacteria from low virulent B. xylophilus made better use of amino acids. In conclusion, endophytic bacteria widely exist in B. xylophilus from different pines and areas; and B. xylophilus strains with different virulence possessed various endophytic bacteria and diverse carbon metabolism which suggested that the endophytic bacteria species and carbon metabolism might be related with the B. xylophilus virulence.
松材线虫病（PWD）由松材线虫（PWN）引起，是松属植物最具破坏性的疾病之一。因此，松材线虫被列为中国最具危险的森林害虫之一，值得检疫。松材线虫的毒力与其传播密切相关。然而，导致松材线虫毒力的主要因素仍不清楚。最近，松材线虫携带的附生细菌引起了广泛关注。但关于内生细菌与松材线虫毒力的关系知之甚少。在这项研究中，用 2 年生黑松苗测试了来自中国六个省不同地区的 10 株松材线虫和 4 种松树的毒力。从不同毒力的松材线虫中分离内生细菌，以研究内生细菌与松材线虫毒力的关系。同时，利用 Biolog 板（ECO）分析了高毒力和低毒力松材线虫内生细菌的碳代谢。结果表明，10 株松材线虫表现出广泛的毒力。同时，从 90%的松材线虫菌株中分离出内生细菌。通过分子和生化方法鉴定，线虫内生细菌的优势种为寡养单胞菌属、不动杆菌属、黄单胞菌属、赖氏菌属、根瘤菌属和假单胞菌属。此外，S. maltophilia 和 A. xylosoxidans subsp. xylosoxidans 是主要菌株。大多数（80%）来自马尾松的菌株含有 S. maltophilia、A. xylosoxidans 或两者。内生细菌利用碳源的能力存在差异。高毒力松材线虫的内生细菌对碳水化合物和羧酸的利用率相对较高，而低毒力松材线虫的内生细菌对氨基酸的利用率较高。综上所述，不同松树和地区的松材线虫中广泛存在内生细菌；不同毒力的松材线虫具有不同的内生细菌和不同的碳代谢，表明内生细菌的种类和碳代谢可能与松材线虫的毒力有关。
