Assessment of Genetic Diversity in Sweet Orange [Citrus sinensis (L.) Osbeck] Cultivars of India Using Morphological and RAPD Markers

Citrus sinensis (L.) Osbeck (sweet orange) is one of the most important commercially cultivated fruit crops of Citrus and occupies the second position after mandarins in India. Genetic diversity and inter-relationship among 22 cultivars of C. sinensis were analyzed based on morphological and RAPD markers. A total of 99 bands were generated with 20 RAPD primers, out of which 51 bands were polymorphic (51.83 %). A pair-wise similarity value between cultivars ranged from 0.48 to 1.00 (avg. 0.77). Moderate levels of polymorphism and high genetic similarity within C. sinensis suggested that cultivars have a low level of genetic diversity despite having high morphological variability. A dendrogram generated based on UPGMA separated all the cultivars into two main clusters in which two cultivars, Delta Valencia and Sweet Orange, showed distinctiveness from the rest of the cultivars. A two-dimensional plot generated from principle component analysis of RAPD data also supported the clustering pattern of dendrogram. Some primers were able to generate unique fragments, which can be used for identification of the cultivars. This study indicated the presence of low genetic diversity within C. sinensis, which could be explained by the fact that much of the phenotypic variation observed may be because of some somatic mutations.