两株我国南北松材线虫虫株形态指标与致病力比较

Comparison of morphological index and pathogenicity of two isolates of Bursaphelenchus xylophilus in southern and northern in China

【目的】松材线虫(Bursaphelenchus xylophilus)是世界多国公认的重大外来入侵物种,可引起松树大量死亡。目前,该虫已扩散至我国辽宁省的多个区县,打破了松材线虫最适温度线。通过对不同地理来源的两株松材线虫虫株的比较研究,试图阐释松材线虫向我国北方快速扩散的原因。【方法】通过比较我国南方松材线虫虫株AMA3和北方松材线虫虫株FCBX的形态指标值、不同温度条件下在灰葡萄孢培养基上的繁殖力,进而测定两虫株对黑松的致病力以及在黑松体内的繁殖量差异,解析松材线虫在我国北方地区的适应性。【结果】虫株AMA3和FCBX在形态学特征上无显著差异,均在伞滑刃属线虫测量范围之内;在15~35℃范围内,北方虫株FCBX和南方虫株AMA3在灰葡萄孢培养基上,随着温度的升高,繁殖量逐步增加。且FCBX虫株的繁殖数量除在30℃条件下稍低外,在其他温度条件下繁殖量均高于AMA3的繁殖数量。在低温(15~20℃)条件下,FCBX虫株的繁殖数量远高于AMA3虫株,差异显著;接种AMA3和FCBX后,黑松感病程度具有差异,FCBX相对于AMA3的致病力更强。在接种35 d后,FCBX的对黑松死亡率达到80%,感病指数为85;而AMA3对黑松的死亡率为60%,感病指数为73;接种35 d后,FCBX在黑松体内的繁殖数量大于AMA3虫株,但差异不显著。【结论】与南方虫株AMA3相比,北方虫株FCBX在灰葡萄孢上的繁殖能力、黑松体内的繁殖数量、对黑松的致病力等方面更强。松材线虫已突破最适温度线,在北移过程中经过了低温驯化,在低温条件下具有更强的繁殖能力和对低温的适应性。

【Objective】 The pine wood nematode, Bursaphelenchus xylophilus, is an invasive species that damages pine trees, with significant ecological and financial consequences around the world. In China, the species has recently breached its optimal temperature line and has now spread to several districts in Liaoning Province. In this paper, we outline the reasons for the rapid spread of B. xylophilus to northern China by compiling evidence about its temperature adaptability. We compare two isolates, from southern and northern China, to understand differences in pathogenicity and reproductive ability. 【Method】 We compared the morphological index values of the southern B. xylophilus strain AMA3 with the northern B. xylophilus strain FCBX. We tested the virulence and reproductive ability of both strains of B. xylophilus in Pinus thunbergii material to assess its adaptability. We used a culture of Botrytis cinereal, a fungus which contributes to pine disease, to simulate field pathogenicity conditions, under different temperature conditions.【Result】There were no significant differences in the morphological index values of AMA3 and FCBX, all of which were typical of Umbellifera nematodes. Both strains were cultured with B. cinereal in the temperature range of 15-35 ℃, and we found that increases in temperature correlated with increases in reproduction. Reproduction of FCBX strains was generally higher than that of AMA3 strains, although this was reversed at-30 ℃. At low temperatures(15-20 ℃), FCBX produced significantly more replicates than AMA3 did. After vaccination against AMA3 and FCBX, P. thunbergii specimens had different susceptibility to disease, although FCBX maintained a higher relative pathogenicity than AMA3. Thirty-five days after inoculation, P. thunbergii specimens exhibited a mortality of 80% when infected with FCBX, and the disease index was 85;samples infected with AMA3 had a mortality of 60%, and the disease index was 73. Over this period, FCBX reproduced more than AMA3 strains in the P. thunbergii samples, but this difference was not significant. 【Conclusion】 Compared with southern strains(AMA3), northern B. xylophilus strains(FCBX) had slightly larger morphological indicators, higher reproductive capacity in B. cinereal, activity ability, higher reproduction in P. thunbergii, and greater pathogenicity. As B. xylophilus has moved northward, it has been subject to low temperature conditions, and we suggest it has acclimatized to these conditions. It has now broken through its optimal temperature line, and northern strains exhibit strong reproductive capacity, high pathogenicity and adaptability to low temperature conditions.