The Pine Wood Nematode (B. xylophilus), a nematode of microscopic size, is currently considered as the greatest threat of invasive pests to the pine forests of Eurasia.
Although of small dimension it has a great reproduction capacity and represents a serious threat to pine stands, mainly Pinus pinaster because it is an agent that causes the “pine wilt disease”.
Pine disease is favoured by high temperatures and periods of drought, but the pine nematode (Bursaphelenchus xylophilus) can also persist in hosts without symptoms in areas not prone to pine disease.
In the study recently published in the journal “Plant Pathology”, issue of the “British Society for Plant Pathology”, the team of CEF researchers analysed the behaviour of the pine wood nematode in two areas with mild winters and where it is known that the pine wood nematode is widespread in local forests: southwestern Europe (Portugal) and southeastern USA (Louisiana).
The team of researchers compared separately the behavior of B. xylophilus in southwestern Europe (Portugal) and southeastern USA (Louisiana). The species P. pinea, P. pinaster, and P. radiata were tested in both areas with inoculations of local B. xylophilus strains. P. sylvestris in Portugal and P. palustris in the USA were also tested. E
Mortality was low, as expected, but the establishment of nematodes was common, with P. sylvestris and P. radiata species having higher nematode density and P. pinaster, P. pinea and P. palustris being more tolerant.
The results of the inoculation experiment with local pine nematode isolates were similar in the Portuguese and North American experiments.
However, the results contradict the hypothesis that North American pine nematodes have such a low virulence that they are necessarily saprophytes, as previously proposed.
The fast growing species (P. radiata and P. pinaster) proved to be more likely to be symptomless carriers in areas not prone to pine disease development. Species adapted to the cold (P. sylvestris) may still be the appropriate hosts for the pathogen, even in the sublethal conditions of their distribution areas.
Overall, the results of this study indicate that the ecology and life cycle of the pine species work as a better indicator of resistance/tolerance to the pine nematode than its geographical origin, even in sublethal conditions with lower temperatures and high humidity.
The fast-growing pine species, with characteristics to develop in high levels of resources, invest less in constitutive defense and may be more likely to be carriers without symptoms in areas not prone to the development of pine disease. Species adapted to the cold may still be susceptible to the pathogen, even in the sublethal conditions of their areas of distribution.
The primary and secondary chemistry of the pine phloem can represent a good indicator of the susceptibility of the pine species that have not yet been challenged by B. xylophilus.
Pimentel, CS, McKenney, J, Firmino, PN, Calvão, T, Ayres, MP. Sublethal infection of different pine species by the pinewood nematode. Plant Pathol. 2020; 00: 1– 9. https://doi.org/10.1111/ppa.13241