A new insight on genetic diversity of sweet oranges: CAPs-SSR and SSR markers

Citrus species are among the most important and widely consumed fruit trees in the world and are subjected to increasing global cultivation. Sweet orange (Citrus sinensis L. Osbeck) is one of 30 species of citrus which is cultivated in different regions of Iran. In this study, 80 trees of 13 sweet orange cultivars of Mazandaran province were studied for genetic diversity and fingerprinting by five short simple repeat (SSR) marker.

The studied cultivars showed a high degree of genetic variability with an average genetic polymorphism of 98.46%. Behshahr and Jadeh Ghadim2 genotypes had the highest and lowest values in Nei genetic diversity, number of effective alleles, and Shannon index, respectively. Based on k-means clustering, the studied genotypes were divided into two main different groups. The high magnitude of genetic similarity between replicates of different cultivars indicated a potential case of homonymy or synonymy. DAPC analysis showed genetic admixture among some of the cultivars. The heatmap plot illustrated the alleles involved in cultivar differentiation. The CAPs analysis of monomorphic alleles of SSR loci indicated that these alleles differ in their sequences which add up to the genetic variability of citrus germplasm.

In general, SSR markers, due to their codominant nature and abundance in genome, are a good indicator for cultivar fingerprinting and hybrid prediction in orange cultivars. The present results showed the high diversity of sweet orange trees in different cultivars in the north of the country.