Effect of Geographic Origin and Ex Situ Growing Site on Phenology, Morphology, and Seed Yield of Yarrow (Achillea millefolium L.) Germplasm from the Rhaetian Alps, Italy

Species adapted to prevailing soil and climatic conditions and native to the same geographic context are increasingly recommended for ecological restoration at high altitude. Better knowledge is required on the level of variation within these species for morpho-physiological traits and seed yield. Adequate and affordable seed production is a prerequisite for native species to be widely adopted for restoration interventions. This study evaluated the variation of yarrow (Achillea millefolium L.) germplasm collected in the Rhaetian Alps, Italy. The worth of yarrow for restoration at high altitude has been repeatedly noted. The main goal of the study was to identify promising materials for selection purposes. The explored mountain section harbored valuable variation for traits of interest. Altitude, climate, and soil should frame an ecological correspondence between the collection site and the target restoration site, to secure the value of the native germplasm outside the boundaries of its collection area. The work also assessed any interaction between the germplasm and the ex situ growing environments, represented by a mountain and a lowland site, and verified the feasibility of the latter for seed multiplication. The growing site remarkably affected several morpho-physiological characters. The lack of difference in mean seed yield between the two altitude-contrasting sites suggested that seed multiplication of yarrow could also be conveniently carried out in lowland environments, with advantages in terms of production costs. Nonetheless, different yield responses in the two sites were observed, emphasizing the need of choosing the material to multiply based on the environment adopted for seed production.