Assessing argan tree (Argania spinosa (L.) skeels) ex-situ collections as a complementary tool to in-situ conservation and crop introduction in the Mediterranean basin

Key message: The argan ex-situ collections help its crop breeding and conservation in the Mediterranean basin, specifically in the southern Iberian Peninsula, where climatic refuges and new cultivation areas could be established. Abstract: A. spinosa (L.) Skeels, hereafter argan, is a tree species naturally distributed in Morocco and Algeria, introduced mainly for productive purposes in countries, such as Tunisia, Israel, and Spain. This promising species has a more extensive potential cultivation and use due to its economic prospects in human food and cosmetics. These reasons and its great aridity adaptation have raised the strategic value of argan and its ex-situ collections, compared to other more sensitive to climate change crops. From this perspective, this study aims to evaluate the genetic diversity of an ex-situ, 10-year-old collection on more than 600 specimens raised in southern Iberian Peninsula, and to promote its cultivation in the most suitable regions for its introduction throughout the Mediterranean basin. To this end, the genetic and morphological diversity of a subset of selected specimens was compared, and six MaxENT models were trained using 96 occurrence points in both wild and cultivated localities (ex-situ collections), together with six bioclimatic variables in a current timeframe and under two climate change scenarios (optimist and pessimist). Surprisingly, this Iberian collection’s genetic diversity was highly representative of the wild population’s diversity in their natural range. Given this representativeness, these cultivars could be a complementary conservation tool as well as a starting point for domestication, breeding, and cultivation programs in a wide environmental range in these territories. The natural distribution of argan will be considerably reduced and shift towards northern habitats by 2050 and 2080, where climatic refuges and new cultivation areas could be established.