Identification and genetic analysis of the pinewood nematode Bursaphelenchus xylophilus from Pinus yunnanensis

摘要

In China, pinewood nematode (PWN), Bursaphelenchus xylophilus, was first discovered from Pinus thunbergii in 1982. Thus far, 14 species in the genus Pinus have been reported to be infected by PWN under natural conditions. Pinus yunnanensis, a pine species native to south-western China, is considered a pioneer tree for barren hill afforestation in areas undergoing rocky desertification. In this study, we detected PWN in dead P.yunnanensis trees in Anlong County, Guizhou Province, China, using both morphological and molecular methods. To our knowledge, this is the first report of PWN from P.yunnanensis in China. To investigate the possible origin of this new outbreak, mitochondrial cytochrome oxidase gene subunit I and cellulase gene sequences were used to evaluate genetic relationships among worldwide PWN isolates. Phylogenetic tree and haplotype networks revealed that the Anlong isolate (BxChQAL008) sequence was identical to those of seven Chinese isolates collected from Sichuan, Chongqing, Zhejiang, Anhui and Shandong (372-1500km from Anlong County), but different from the isolate BxChQZY030 collected from the same province (330km from Anlong County). It is suggested, therefore, that more than one introduction of PWN into Guizhou Province has taken place. The Anlong isolate was likely introduced from neighbouring or more distant provinces rather than from outside China. Moreover, the absence of a correlation between geographic and genetic distance was observed using Mantel test analysis, providing evidence that human-induced dispersal plays a fundamental role in the spread of the PWN in this region.