Title : WHY ARE SOME PINE SPECIES RESISTANT TO PINE WILT DISEASE?
The Pine Wood Nematode (PWN), Bursaphelenchus xylophilus, is undoubtedly the most important pathogen affecting pines worldwide. In Portugal and Spain, the nematode´s main host is maritime pine Pinus pinaster, with P. sylvestris also affected, while other species such as stone pine (P. pinea) and Aleppo pine (P. halepensis) are not affected. The reasons for the differences on the susceptibility between hosts are not known, but may result from a combination of both anatomical (constitutive) and/or biochemical mechanisms of defence, which need to be directly compared between susceptible and resistant species. In this study, small branches were collected from living 12-year old pine species (the four mentioned pine species, with n=5 for each species) without the presence of the PWN, and from pines 24 hours and 72 hours after artificial nematode inoculation. Through histological techniques the samples were anatomically analysed, mainly to the dimension of resin canals, the lignified cells and the phenolic compounds, as well as to cellular differences after infection. Comparing the four pine species the results obtained showed anatomical differences, for the cortical and xylem resin canals, as well cells content differentiation after infection. Moreover, the histochemical tests in both resistant/tolerant species detected a greater amount of phenolic compounds 24h after infection, as the first response against B. xylophilus. Furthermore, biochemical factors involved in the tolerance/resistance to pine wood nematode were analysed through HPLC.
Studies are ongoing, with the objective of clarifying the host´s defence mechanisms against the nematode´s attack, and to discriminate the importance of the constitutive and induced anatomical and biochemical structures to wilt resistance and susceptibility.