Analysis of genetic diversity of Moroccan natural carob (Ceratonia siliqua L.) populations using ISSR markers

To assess the genetic diversity and structure of Carob tree (Ceratonia siliqua), 12 natural populations representing its main geographical range in Morocco, were examined using ISSR markers. The 18 ISSR primers used produced 182 clear and reproducible bands, of which 141 (76.66%) were polymorphic. Levels of variation were variable by population, and a mean value for PIC of 0.47 indicating high diversity in the studied material was obtained. Moreover, the results of the global AMOVA analysis showed that 74.20% of the total genetic variability resided within populations and the remaining (25.80%) occurring between populations. Besides, hierarchical AMOVA revealed very little genetic differentiation between groups of mountain range, bioclimatic and altitudinal conditions (FCT = 1.4%, FCT = 5% and FCT = 0.1% respectively). The populations were revealed genetically largely differentiated (FST = 0.25) and could be the result of limited gene flow estimated at 0.75. Moreover, geographic distances and genetic distances between populations were correlated (r = 0.276; P < 0.001). This indicates that isolation by distance may have played an important role in shaping the genetic structure of this species. The NJ dendrogram and Bayesian model-based clustering approach identified four groups of populations independently of bioclimate, geographic origin and bioclimate of studied populations. The obtained results provide crucial information on the genetic diversity and structure of this species in Morocco that can be useful for proposing and establishing breeding programs for C. siliqua and creating an effective strategy to preserve this genetic resource.