The walnut (Juglans regia L.) is a traditional fruit crop in Morocco. This species is cultivated in mountain in different environments. However, little data is available on its genetic diversity and its adaptability. Morphological characters of leaf and fruit from 11 Moroccan accessions of walnut were used to assess phenotypic variation of this species. Significant differences were found between accessions for the most examined traits, indicating a high phenotypic diversity. Multivariate analyses lead to identify three groups of accessions. The first group composed by the accessions of both Middle and High Atlas Mountain with high weigh and percentage of kernel and low thickness of shell. The second group included the accessions for the High Atlas Mountain characterised by large leaf, high nut dimension and great nut size. The third group is composed by two accessions, one belongs to the Middle Atlas Mountain and the other originating from High Atlas Mountain, which are characterized by small leaf and nut. Then, the structuration of accessions in three groups was not correlated to the mountain range type. Moreover, this study showed a significant phenotypic heterogeneity between the eleven studied accessions which opens the way for the strategies for their conservation and the selection of efficient genotypes with the desired traits.

The genetic diversity and genotypes structure of walnut (Juglans regia L.) are essential to understand and manage genetic resources of this species, as well as for further progress in breeding programs. ISSR markers were used to assess the genetic diversity of 66 individuals’ trees from 11 accessions, representing the main cropping area of walnut belonging to two ranges types of Mountain in Morocco: middle and high Atlas. Eleven ISSR primers rendered a total of 135 bands (91%) with 0.88 polymorphic information content. The utilization of 123 polymorphic bands revealed a high level of genetic variation within and among the examined accessions. The multi-locus values of Ht and Hs were 0.25 and 0.20, respectively. The AMOVA analysis showed that 71.30% of total genetic variability is accounted within accessions and 28.70% between accessions. This was congruent with the coefficient of genetic differentiation (GST=0.16). Bayesian model-based clustering approach identified three gene pools that were not correlated with mountain range type. This is the first application of ISSR markers for the assessment of genetic diversity in Moroccan germplasm of walnut. This information will be useful to define conservation strategies and improvement programs of this species.