Characterisation and assessment of genetic diversity in cultivated and wild carob (Ceratonia siliqua L.) genotypes using AFLP markers

Carob (Ceratonia siliqua L.) is a trioecious evergreen legume tree native to the Middle East and widespread throughout the Mediterranean as a crop, or as part of the maquis. Amplified Fragment Length Polymorphism (AFLP) markers were used to estimate intra-specific genetic diversity among 41 carob genotypes from different areas of the eastern and western Mediterranean basin. Italian and Spanish cultivated varieties were included in the study for fingerprinting. A total of 96 unambiguous polymorphic loci were scored from seven Eco RI/Mse I primer combinations. Simple matching similarity coefficients between pairs of genotypes ranged from 0.542 to 1.000, indicating a high level of intra-specjfic diversity. AFLP markers clearly discriminated between all the accessions, except for two Sicilian varieties. An UPGMA (Unweighted Pair Group Method with Arithmetic Mean) dendrogram and a Principal Co-ordinates Analysis revealed a broad relationship between the clusters and the geographic origin of the genotypes, with few exceptions. Most of the hermaphrodite varieties belonged to the same cluster, indicating that these cultivars were probably selected in a specific area, then distributed elsewhere. Moreover, an analysis of molecular variance (AMOVA) revealed a high level of "within geographic area" differences.