Assessment of genetic diversity of Tunisian orange, Citrus sinensis (L.) Osbeck using microsatellite (SSR) markers

Citrus are one of the most cultivated crops in the world. Economically, they are very important fruit trees in Tunisia. Little is known about the genetic diversity of the Tunisian Citrus germplasm. Exploring this diversity is a prerequisite for the identification and characterization of the local germplasm to circumvent and controlling genetic erosion caused by biotic and abiotic stress to aid its conservation and use. In the present study, we explored the genetic diversity of 20 Tunisian orange cultivars [Citrus sinensis (L.) Osbeck] and established their relationships by using seven simple sequence repeat (SSR) loci. In total, 37 alleles and 44 genotypes were scored. The sizes of alleles ranged from 90 to 280 bp. The number of alleles per locus was from 4 to 7, with an average of 5.28. Polymorphic information content value changed from 0.599 to 0.769 with an average of 0.675. Analysis of the genotypes revealed a heterozygote deficiency across all the genotypes. The observed heterozygosity varied from 0 to 1 (average of 0.671). Cluster analysis showed that three groups could be distinguished and the polymorphism occurred independently of the geographical origin of the studied orange cultivars. The detected SSR genotypes allowed the establishment of an identification key with a discriminating power of 100%. Multivariate analysis and the neighbor-joining phylogenetic tree indicated a narrow genetic base for the orange cultivars. The usefulness of SSR markers for orange fingerprinting and evaluation of the genetic diversity in the Tunisian germplasm are discussed in this paper.