Assessment of Genetic Variability within the Genus Citrus in Syria Using SSR Markers

Aims: The characterization and the estimation of genetic variability between accessions belonging to Citrusgenus using the SSR markers.
Place and Duration of Study: Laboratory of Molecular Genetic, Faculty of Agriculture, Tishreen University, Lattakia, Syria, between August 2011 to March 2013.
Methodology: 114 samples representing 4 groups of Citrus, obtained from the Department of CitrusResearch in Tartous, Syria, were used in this study. DNA was extracted from young leaves and analyzed with 26 SSR primer pairs.
Results: Six primers produced monomorphic alleles, and the other 20 primers produced 95 different alleles. The highest number of alleles (32) was detected in Lemon group while the lowest number (28 alleles) was revealed in Mandarin group. The values of genetic diversity were calculated and ranged from 0.079 in Grapefruit to 0.533 in Mandarin groups. A dendrogram based on the index of genetic distance was established and showing clear separation between Citrus groups where they clustered into two distinct branches. The first one containing cultivars of Lemon group, while the second one included 4 distinct clusters, one for Mandarin cultivars group, one for sweet orange group, one for Grapefruit and pumelo and the fourth one for Kumquat accessions.
12 specific alleles were identified; they will be a helpful tool in the Citrus breeding programs.
Conclusion: The results obtained in the present work proved the utility of SSR markers for evaluating the genetic diversity and relationships between Citrus species maintained in the Department of Citrus Research in Tartous, Syria, and showed high level of genetic similarity within each cultivar and within the species of Grapefruit and of Sweet orange at the tested SSR loci.