Resin-based response of Pinus pinaster and P. radiata during infection by Fusarium circinatum

Pine pitch canker, caused by the fungus Fusarium circinatum, is a disease of economic and ecological importance worldwide. In Spain, Pinus radiata and P. pinaster are the two species most affected by the pathogen. Pinus radiata is one of the most susceptible species to the disease, while P. pinaster is moderately resistant. As part of the defensive response to invading organisms, pines contain and de novo synthesize resin, mainly composed of terpenes. Resin is accumulated and produced in constitutive and induced resin ducts. We compared the anatomical resin system and terpene profiles in both species infected with F. circinatum to better understand the resin-based defense mechanisms against this pathogen. We also used a previous transcriptomic study of the interaction between P. pinaster and F. circinatum to analyse the expression of terpene-related genes. This study shows that the F. circinatum-susceptible species P. radiata induced larger resin ducts and produced more resin than the moderately resistant P. pinaster, a result similar to that observed with other pathogens that use resin ducts to colonize the host. By comparing the terpene profiles of both species, we identified some terpenes that may contribute to the differential resistance between species. This study provides comprehensive information on terpene content and profiles.