Mycobiome of Pinus pinaster trees naturally infected by the pinewood nematode Bursaphelenchus xylophilus.

Fungi are important biological elements in the Pine wilt disease (PWD) complex. In the late stages of the disease, the pinewood nematode (PWN) Bursaphelenchus xylophilus feeds on the fungal flora available in the pine tree for survival and multiplication. Previous studies have confirmed a close relation between the PWN and blue-stain fungi (Ophiostomatales), which are necrotrophic pathogens associated with bark beetles (Coleoptera: Scolytidae). The PWN is able to grow densely in the presence of these fungi, which results in a higher number of nematodes transferred to the insect-vector Monochamus spp. To understand the spatial diversity and structure of Pinus pinaster mycobiome, wood samples from PWN-infected and non-infected pine trees were collected in three locations of Continental mainland Portugal with different PWD records, during the maturation phase of the insect-vector M. galloprovincialis (winter 2019-spring 2020). The PWN-mycobiome from the PWN-infected P. pinaster was also characterized. A total of 27 samples of P. pinaster and 13 samples of PWN from PWN-infected trees were characterized using ITS2 amplicon sequencing. The diversity and structure of the fungal communities in P. pinaster varied with disease status suggesting that the PWN presence affects the endophytic fungal communities. For both P. pinaster and PWN fungal communities, differences were also associated with locations (recent PWD loci Seia, and long-term PWN locus Companhia das Lezírias and Tróia). Ophiostomatales were mainly detected in PWN-infected P. pinaster. This research contributes to increase the knowledge on the ecology of the fungal communities in PWD complex.