Characterisation of Juglans regia L. with SSR markers and evaluation of genetic relationships among cultivars and the 'Sorrento' landrace

Juglans regia L. 'Sorrento' is the most important Italian walnut variety. It is cultivated for both nuts and timber in the Campania Region. 'Sorrento' is a mixture of genetic entities and is best characterized as a 'landrace', which affects the homogeneity of important commercial parameters such as fruit size and yield. To clarify the genetic variability in walnuts grown in Campania and labelled as 'Sorrento', we analyzed ten plants that originated from 'Sorrento' seeds and six grafted 'Sorrento' clones, and compared them with six other walnut cultivars using Simple Sequence Repeats (SSRs) DNA markers. Primers derived from J. nigra L. amplified alleles at six SSR loci in Persian walnut. A total of 33 putative alleles were detected, nine of which were unique to one genotype. Two loci, WGA5 and WGA27, were particularly useful for distinguishing walnut varieties. Cluster analysis clarified the relatively large genetic distance between most of the 'Sorrento' plants and some genotypes labelled as 'Sorrento'. Despite the genetic diversity found among seed and vegetatively propagated plants, 'Sorrento' landrace trees can be identified and distinguished from other walnut varieties. These data present a starting point for characterising the range of genetic variability among 'Sorrento' plants.