The pinewood nematode, Bursaphelenchus xylophilus, is native to North America but it only causes damaging pine wilt disease in those regions of the world where it has been introduced. The accurate detection of the species and its dispersal routes are thus essential to define effective control measures. The main goals of this study were to analyse the genetic diversity among B. xylophilus isolates from different geographic locations and identify single nucleotide polymorphism (SNPs) markers for geographic origin, through a comparative transcriptomic approach. The transcriptomes of seven B. xylophilus isolates, from Continental Portugal (4), China (1), Japan (1) and USA (1), were sequenced in the next generation platform Roche 454. Analysis of effector gene transcripts revealed inter-isolate nucleotide diversity that was validated by Sanger sequencing in the genomic DNA of the seven isolates and eight additional isolates from different geographic locations: Madeira Island (2), China (1), USA (1), Japan (2) and South Korea (2). The analysis identified 136 polymorphic positions in 10 effector transcripts. Pairwise comparison of the 136 SNPs through Neighbor-Joining and the Maximum Likelihood methods and 5-mer frequency analysis with the alignment-independent bilinear multivariate modelling approach correlated the SNPs with the isolates geographic origin. Furthermore, the SNP analysis indicated a closer proximity of the Portuguese isolates to the Korean and Chinese isolates than to the Japanese or American isolates. Each geographic cluster carried exclusive alleles that can be used as SNP markers for B. xylophilus isolate identification.

The root lesion nematode Pratylenchus penetrans is an important plant-parasitic nematode of potato. In this study, the susceptibility of commercial potato cultivars to P. penetrans was assessed. Nematode penetration was evaluated in cultivars Agria, Camel, Kennebec, Laura, Royata, and Stemster at 1, 3, 7, and 15 days after inoculation (DAI) with 750 nematodes/plant, and an egression assay at 3 DAI with 1000 nematodes/plant. Reproduction assays of cultivars Agata, Agria, Camel, Désirée, Dirosso, Kennebec, Laura, Picasso, Royata, and Stemster were performed in 2 L pots inoculated with four P. penetrans/g soil and quantified at 60 DAI. Tenue or moderate root cell browning to advanced necrotic areas were observed after nematode penetration, and the number of nematodes/g of root gradually increased with time of infection. A lower number of deposited eggs and nematodes were observed within the roots of cultivar Laura in all assays comparatively to other cultivars. The susceptibility index (SI) was significantly lower in cultivar Laura (0.4–0.6), followed by cultivars Camel and Picasso (0.8–0.9). All remaining cultivars showed SI values above 1. Although the potato susceptibility to the nematode varied among cultivars, no differences on the average number or weight of tubers produced by each plant of inoculated versus non-inoculated plants were detected. Our data reveals that these cultivars have a distinct ability to support the reproduction of P. penetrans.