Identification of 57 sweet orange cultivars using AFLP markers

Sweet orange (Citrus sinensis) represents an important group of Citrus fruit; however, the identification of sweet orange cultivars during vegetative growth can be difficult. A study on the genetic identification of sweet orange cultivars may be significant for the sweet orange nursery industry, for cultivar-rights protection, and is important for the genetic evaluation and conservation of these orange cultivars. In this study, amplified fragment length polymorphism (AFLP) markers were used to genotype 57 sweet orange cultivars. Ten PCR primer pairs generated 629 unique AFLP bands, with a size range of 50 - 500 bp. Seventy-four bands (11.8%) were polymorphic. On average, each primer pair produced 62.9 fragments, with 7.4 polymorphic fragments. A dendrogram of the 57 sweet orange cultivars was constructed based on an UPGMA analysis using Jaccard's coefficients of similarity. This provided a clear comparison of the genetic variation between cultivars and an ability to identify them. From Jaccard's coefficients, 56 of the 57 cultivars examined were genetically close, with coefficient values >= 0.985. 'Variegated Navel' was less closely-related, with a much lower coefficient value (0.94). Among the 57 cultivars, 28 sub-groups, some consisting of only one cultivar, could be separated by their AFLP fingerprints. Compared to ISSR and SSR markers, AFLP seemed to be the preferential marker technique for the identification of sweet orange cultivars.