DdRAD sequencing and morphometric data analysis reveal a clear differentiation among the Tunisian populations of Onopordum nervosum ssp. platylepis Murb

Onopordum nervosum ssp. platylepis Murb, an endemic plant in Tunisia, Algeria, and Libya, with spiny leaves and distinctive spiny-winged stems from the Asteraceae (Compositae) family, is used as a vegetable rennet in the production of traditional cheese. In Tunisia, the species is threatened and occurs in fragmented small populations isolated from each other. This study aims to evaluate the germplasm diversity of wild Onopordum platylepis to support future breeding efforts and aid in discriminating among populations with interesting phenotypic traits. Morphological characterization was conducted on five populations identified in the North (Tunis, Nabeul) and the center of Tunisia (Sousse, Kairouan, Monastir) to identify relationships among them. This involved adapting certain UPOV (International Union for the Protection of New Varieties of Plants) descriptors for Cynara cardunculus L. (cardoon) along with additional specific traits. Results revealed significant differences among the studied populations for the majority of traits with Kairouan (KN) population producing the greatest amount of biomass and flower heads. Additionally, a double-digest restriction-associated DNA sequencing study was conducted on O. platylepis individuals to confirm population differentiation. Results showed that Kairouan (KN) population provided the highest genetic diversity (pi = 1.5 x 10-3). Comparisons of pairwise Fst values between populations ranged from 0.1 to 0.13 and negative inbreeding coefficient (FIS) values were observed. According to our findings, the studied populations revealed important differentiation and maintained a moderate level of genetic diversity through frequent outcrossing or sequential gene flow. Both morphological and molecular analyses unveiled a distinct correlation between population structure and geographical distribution. Two distinct clusters were identified for the populations from the north and the center, suggesting that spatial segregation has resulted in lower genetic relatedness between these populations. In this context, it is important to monitor and reduce anthropogenic activity to protect genetic diversity, as well as ensuring the resilience of O. platylepis to environmental and climatic changes.