Pseudotsuga menziesii: pathogens introduced and whose introduction is feared.
According to European and Mediterranean Plant Protection Organization (EPPO) forecasts, the climatic conditions favourable to Douglas fir in many European countries could prove suitable also to those pathogens whose possible introduction is feared. Already around the twenties of the last century, on the other hand, two pathogens specific of this tree species, Rhabdocline pseudotsugae and Phaeocryptopus gaeumanni, made their appearance in Europe and in Italy. In subsequent years, P. menziesii var. menziesii, the species mainly employed in Italy in new plantations, was damaged only by Heterobasidion annosum sensu stricto. However, in an undefined time, this species could face new infectious processes induced by alien pathogens, which might also come from other continents. Concerning Douglas fir, among the alien pathogen species whose possible introduction is feared, in accordance with the EPPO, deserve to be mentioned: Al List (organisms absent from the EPPO region): Ophiostoma wageneri, Phellinus weirii, Arceuthobium douglasii. A2 List (pests present only in some EPPO countries): Phytophthora ramorum, present in Italy on Rhododendron and Viburnum. Gibberella circinata, reported in Italy on Pinus pinea and P. halepensis; Botryosphaeria laricina, Melampsora medusae. EPPO Alert list (harmful organisms posing a risk of spread in member countries): Mycosphaerella pini. The current trend to warming that is affecting Europe and Italy will favour the more thermophilic or thermotolerant alien pathogens, but also, with the time, those ecotypes that will better adapt to a changing climate. Following the first infectious processes, already in the 70s of the 1900, high density pure stands were not recommended and it was suggested to use green Douglas fir, which is resistant to R. pseudotsugae. Today, if on one hand we are bound to the strict EPPO regulations, on the other hand we can pursue novel approaches: reconstruction, through DNA fingerprinting, of the introduction and dispersal pathways of plant pathogens; study of their genetic diversity; estimate of the evolutionary potential of introduced pathogens; development of accurate forecasting models; set up of permanent monitoring protocols. Phytosanitary management (including monitoring, preferably permanent) of existing plantations and of new ones will be in any case fundamental, according to silvicultural techniques pursued in Italy.