Genetic resources of Tunisian Artemisia arborescens L. (Asteraceae), pattern of volatile metabolites concentration and bioactivity and implication for conservation

Artemisia arborescens L. (Asteraceae) is an endemic and a valuable medicinal and ornamental species in the Mediterranean regions. Despite the interest given to A. arborescens L. as promising medicinal crop, this species is becoming threatened of extinction in Tunisia as a result of the fragmentation of its habitat and the absence of any specific measures for its conservation and valorisation. Based on the last considerations, extent information about their volatile metabolites profiling, contents and antimicrobial potential were undertaken based on fourteen populations originated from various geographical and bioclimatic habitats of Tunisia. The obtained results reveal an essential oil content mean value of 1.47%. The leaves of Tunisian tree wormwood populations were dominated by camphor (15.05-58.05%), chamazulene (11.72-45.26%) and beta-thujone (0-36.53%). Based on the three first major compounds detected for each population, four different oil types were defined (Oil type I: camphor-chamazulene-beta-thujone; Oil type II: camphor-chamazulene-terpinen-4-ol; Oil type III: camphor-chamazulene-bornyl acetate; Oil type IV: camphor-chamazulene-linalool). PCA, HCA and Heatmap chemometric analyses revealed three classification clusters defined mainly by minor compounds. These minor volatile metabolites succeed to discriminate among the fourteen studied populations which promote their chemotaxonomic interest. Our findings confirm previous reports concerning this species in the world and show chamazulene, camphor and beta-thujone as the major compounds of this species which define their well known chemotypes independently of the geographical, bioclimatic and genotypic factors. This makes of these three components promising chemosystematic tool for the discrimination of A. arborescens L. in the genus Artemisia. The results showed that the four tested oils were effective against the nine tested microbial strains. The highest antimicrobial potential was revealed for the population AAr_MB characterized by camphor, chamazulene and beta-thujone as the dominant components. The pattern of essential oils concentration offers wide range of possibilities for the initiation of breeding programs according to the desired bioactive compounds. Both in situ and ex situ conservation strategies were suggested for the maintenance of the highest chemical polymorphism of this valuable medicinal species.