Genetic diversity of pine-parasitic nematodes Bursaphelenchus xylophilus and Bursaphelenchus mucronatus in China

The internal transcribed spacer (ITS) regions of rDNA have been routinely employed for identification and phylogenetic analysis of many nematode species. In this study, the intra- and interspecies ITS genetic diversity of Bursaphelenchus xylophilus and Bursaphelenchus mucronatus was evaluated. Ninety-one isolates of the two nematode species collected from 14 Chinese provinces, Japan and Korea were used for ITS-PCR and sequencing. An unweighted pair group cluster analysis dendrogram clustered them as two B.mucronatus and one B.xylophilus independent clades. Principal component analysis showed the phylogenetic relationship of the two nematode species more clearly; B.mucronatus isolates were separated into more than four groups, whereas B.xylophilus isolates still clustered into a group. The results of the Mantel test indicated the correlation of genetic distance matrices and geographic distance matrices was significant for both nematode species. The genetic differentiation coefficient (G(st)) and gene flow (N-m) of B.mucronatus were 0.341 and 1.091, respectively, suggesting the importance of landscape heterogeneity and considerable obstacles for genetic exchange among B.mucronatus isolates in China. However, G(st) and N-m of B.xylophilus were 0.188 and 2.151, respectively, very different compared to B.mucronatus. This could be owing to the short-term introduction of B.xylophilus into China and a rapid spread through anthropogenic pathways. Our work adds to the understanding of the genetic diversity and genetic relationship of the two pine-parasitic nematode species, and will aid in controlling them in the future.