Genetic diversity in Tunisian Crataegus azarolus L. var. aronia L. populations assessed using RAPD markers

The genetic diversity of nine wild Tunisian Crataegus azarolus var. aronia L. populations from different bioclimates was assessed using RAPD markers. Eight selected primers generated a total of 105 bands, 81 of which were polymorphic. Shannon's index (H') ranged from 0.222 to 0.278 according to a population with an average of 0.245. The genetic variation within the species (H-SP = 0.423) was relatively low. A high differentiation (G(ST) = 0.421) among populations coupled with a low level of gene flow (N-m = 0.472) were observed. The analysis of molecular variance (AMOVA) revealed also significant differentiation among populations (Phi(ST) = 0.371), even at a low scale space. The majority of variation occurred within populations (63.31%). The Mantel test performed on genetic (Phi(ST)) and geographic distance matrices among population pairs did not reveal an isolation by distance. Interpretation of Neighbour-joining tree based on Nei's and Li's genetic distance among individuals showed distinct population groupings. The UPGMA dendrogram based on Phi(ST) values revealed two population sub-clusters, each including populations from different bioclimates and/or geographic regions. The low level of genetic diversity and the high genetic structure of populations resulted from genetic drift caused both by habitat fragmentation and the low size of populations. The high differentiation among populations and the similar low level of diversity within populations suggest that in situ conservation should interest all populations. The ex situ conservation should be based on the collection of seeds rather within than among populations because of the maximum of variation was revealed within populations.