Identification and characterization of common walnut using sequencerelated amplified polymorphisms (SRAP) markers

Abstract

Common walnut is one of the oldest cultivated and economically important nut trees. This study was aimed to analyze 40 walnut germplasms in Xinjiang, China using 12 nut phenotypic traits and 18 sequence-related amplified polymorphism (SRAP) markers. Samples included 22 native cultivars and 18 naturally seeded trees. Statistical results of the phenotypic traits were consistent with those in previous studies regarding walnut germplasm diversity. The SRAP marker system generated 178 alleles, of which 134 were polymorphic. SRAPs could effectively distinguish the genotypes tested and explain the phylogenetic relationships among the cultivars to a certain extent. The genetic similarity levels of nut phenotypes and SRAP markers among the walnut genotypes varied within the range of 54%–95% and 62%–88%, respectively, based on the Jaccard similarity coefficient. Four nutshape traits that are easy to evaluate (namely the shape of the longitudinal section perpendicular to the suture, the prominence of the apical tip, the shape of the apex perpendicular to the suture, and the shape of the base perpendicular to the suture) and 18 SRAP makers with a high distinguishing power were used to fingerprint the 40 walnut germplasms. The fingerprints could distinguish the tested genotypes. Two-dimensional graphical DNA barcodes were generated for rapid and accurate identification of the genotypes to protect intellectual property and assist in breeding studies.