Population structure and evolution of virulence in the pinewood nematode

松材线虫的种群结构和毒力演化

• 批准号: 13460068
• 负责人: TOGASHI Katsumi
• 金额: $ 8.06万
• 依托单位: HIROSHIMA UNIVERSITY
• 依托单位国家: 日本
• 项目类别: Grant-in-Aid for Scientific Research (B)
• 财政年份: 2001
• 资助国家: 日本
• 起止时间: 2001 至 2003
• 项目状态: 已结题
• 来源: https://kaken.nii.ac.jp/en/grant/KAKENHI-PROJECT-13460068/
• 关键词: Bursaphelenchus xylophilus; pathogenicity; virulence; evolution; population structure; microsatellite; water stress; pine trees; 固体群構造

Five microsatellite loci were found in the nuclear genome of Bursaphelenchus xylophilus. Four of them were polymorphic and shown to help the analysis of nematode population structure. A three-year study indicated that frequencies of alleles fluctuated greatly although the mean number of alleles per locus was almost unchanged. There was a little fluctuation in the genetic diversity within a total population. The genetic diversity within nematode subpopulations sampled from individual dead trees or insect vectors decreased, which caused the genetic differentiation to increase between subpopulations. Such genetic change in nematode population had no relation to the change in the virulence (the capability of killing tree). Simultaneous inoculations of virulent and avirulent isolates on Pin us thunbergii trees showed that frequencies of alleles specific to virulent isolates were greater than those specific to avirulent isolates in diseased trees, indicating that virulent isolates proliferated more rapidly than avirulent ones. This shows that the pinewood nematode reproducing sexually satisfies one of the assumptions on which evolutionary theories of virulence by multiple infections are built in parasites and pathogens reproducing asexually. This inoculation experiment also showed appearance of new alleles possibly due to crossing over. The increase in genetic diversity may raise the difference in virulence. However, a three-year inoculation experiment by using two isolates differing in virulence showed no increase in virulence. To identify B. xylophilus and B. mucronatus, two species-specific PCR primer pairs that produce DNA fragments of different lengths were developed. Relaxation in water stress before and after the infection of B. xylophilus on P. densiflora seedlings rarely survived wilt disease.

在松材线虫核基因组中发现了 5 个微卫星位点。其中四个具有多态性，有助于分析线虫种群结构。一项为期三年的研究表明，尽管每个位点的平均等位基因数量几乎没有变化，但等位基因的频率波动很大。总种群内的遗传多样性略有波动。从个体死树或昆虫载体中取样的线虫亚群内的遗传多样性下降，这导致亚群之间的遗传分化增加。线虫种群的这种遗传变化与毒力（杀死树木的能力）的变化无关。在黑松树上同时接种强毒和无毒菌株表明，病树中强毒菌株特异等位基因的频率高于无毒菌株特有的频率，表明强毒菌株比无毒菌株增殖更快。这表明松木线虫的有性繁殖满足了无性繁殖的寄生虫和病原体中建立多重感染毒力进化理论的假设之一。该接种实验还显示可能由于交叉而出现新等位基因。遗传多样性的增加可能会增加毒力的差异。然而，使用毒力不同的两种分离株进行的三年接种实验显示毒力没有增加。为了鉴定松材线虫和松材线虫，开发了两种物种特异性 PCR 引物对，它们可产生不同长度的 DNA 片段。松材线虫感染松材线虫前后水分胁迫的缓解，赤花松苗很少能在枯萎病中存活。

项目成果

Matsunaga, K., K.Togashi: "A simple method for discriminating Bursaphelenchus xylophilus and B. mucronatus by species specific polymerase chain reaction primer pairs"Nematology. 6(in press). (2004)

Matsunaga, K., K.Togashi：“通过物种特异性聚合酶链反应引物对区分松材线虫和松材线虫的简单方法”线虫学。

Matsunaga, K., K.Togashi: "A simple method for discriminating Bursaphelenchus xylophilus and B. mucronatus by species specific polymerase chain reaction primer pairs."Nematology. 6(in press). (2004)

Matsunaga, K., K.Togashi：“一种通过物种特异性聚合酶链反应引物对区分松材线虫和松材线虫的简单方法。”线虫学。

Matsunaga, K., K.Togashi: "A simple method for discriminating Bursaphelenchus xylophilus and B.mucronatus by species specific polymerase chain reaction primer pairs."Nematology. 6(in press). (2004)

Matsunaga, K., K.Togashi：“一种通过物种特异性聚合酶链反应引物对区分松材线虫和松材线虫的简单方法。”线虫学。