First detection of Bursaphelenchus luxuriosae associated with Pinus pinaster in Portugal

During a field survey carried out on symptomatic maritime pine trees (Pinus pinaster) in Góis, central Portugal, Bursaphelenchus luxuriosae was isolated for the first time in Portugal, and in Europe. Identification of the nematodes was based on morphological characters and molecular analyses for this species. The general morphology of both females and males is in agreement with the original description for B. luxuriosae, namely the typical morphology of the male spicules and the conspicuous morphology of female tail. Species identification was confirmed through sequencing of the ITS rDNA region and the fragment spanning the D2/D3 domain of the 28S rDNA gene. This species belongs to the xylophilus-group and is the third species in this group known in Portugal. The nematodes were retrieved in small numbers (<100 nematodes/100 g dry wood), and no insect vector association could be established.

Evidences for an opportunistic and endophytic lifestyle of the Bursaphelenchus xylophilus -associated bacteria Serratia marcescens PWN146 isolated from wilting Pinus pinaster

Pine wilt disease (PWD) results from the interaction of three elements: the pathogenic nematode, Bursaphelenchus xylophilus; the insect-vector, Monochamus sp.; and the host tree, mostly Pinus species. Bacteria isolated from B. xylophilus may be a fourth element in this complex disease. However, the precise role of bacteria in this interaction is unclear as both plant-beneficial and as plant-pathogenic bacteria may be associated with PWD. Using whole genome sequencing and phenotypic characterization, we were able to investigate in more detail the genetic repertoire of Serratia marcescens PWN146, a bacterium associated with B. xylophilus. We show clear evidence that S. marcescens PWN146 is able to withstand and colonize the plant environment, without having any deleterious effects towards a susceptible host (Pinus thunbergii), B. xylophilus nor to the nematode model C. elegans. This bacterium is able to tolerate growth in presence of xenobiotic/organic compounds, and use phenylacetic acid as carbon source. Furthermore, we present a detailed list of S. marcescens PWN146 potentials to interfere with plant metabolism via hormonal pathways and/or nutritional acquisition, and to be competitive against other bacteria and/or fungi in terms of resource acquisition or production of antimicrobial compounds. Further investigation is required to understand the role of bacteria in PWD. We have now reinforced the theory that B. xylophilus-associated bacteria may have a plant origin.