Genetic origin of two Italian provenances I11 and I15 compared to possible eight American IUFRO provenances of Douglas fir (Pseudotsuga menziesii (Mirb.) Franco) from North America

In IUFRO experimental plots of 1969–1970, two 'Italian' provenances, I11 and I15, of unknown genetic origins, have consistently exhibited remarkable performance and stability over time and space in previous studies. It was deemed essential to acquire knowledge about the genetic origin area and conduct a genetic characterization of these two Italian provenances for their formal registration. Considering the observed intraspecific genetic variation across the American geographic cline, it was imperative to ensure that the selected provenances adequately represented diverse eco-physiological regions within the species range. To achieve this, most likely American provenances were selected, building upon historical document hypotheses and aiming to cover various geo-climatic areas. Specifically, five coastal variety and three interior variety provenances were chosen, two for each major geo-climatic region. The results obtained, using seven microsatellites, through four genetic structure analysis methods, predominantly attributed I11 to the area around 1080 origin, Washington Cascades region and 1094, Oregon Coast area. Similarly, I15 was primarily attributed to the area around the 1096 provenances, the Oregon Cascades region, compared to other coastal areas it appeared to differ. Among the three interior origins, 1162 from Arizona, Interior South area, exhibited intermediate genetic characteristics between the two varieties, despite its geographical location falling within the range of the interior variety. Similar to our expectations, comparing the distinct characteristics of the origin areas for each Italian provenance, it becomes feasible to complete their certification as 'seed stands' and to plan an appropriate management strategy for the species' diffusion.