Genetic diversity among germplasms of Pitaya based on SSR markers

Pitaya has been widely cultivated in China and has became an economically important fruit crop. The majority of its germplasm accessions are white and red pulp types and, owing to the lack of standardization, there are serious nomenclature issues. To identify the germplasm resources, genetic diversity levels and relationships among 46 accessions collected from China and abroad were investigated using simple sequence repeat markers. A total of 52 alleles were detected by 18 markers, and the number of effective alleles ranged from 1.1636 to 4.0341, with an average of 2.8624. The genetic similarity coefficient varied from 0.61 to 0.95. Subsequently, based on their geographical distribution, four groups (A, B, C and D) were distinguished by truncating the dendrogram at an 80% similarity level. Group A contained 35 accessions, which were red (pink) pulp genotypes, Group B contained 5 white pulp accessions; Group C contained 4 accessions with similar identities, and Group D contained only two accessions, cactus and Epiphyllum oxypetalum. Additionally, most of the red pulp genotypes in Group A came from Taiwan. The results indicated that the selected germplasms have a rich genetic diversity and underwent genetic separation during dispersal.