Genetic diversity among wild forms and cultivated varieties of Discus ( Symphysodon spp.) as revealed by Random Amplified Polymorphic DNA (RAPD) fingerprinting

Abstract

Trial-and-error method has been used extensively in the breeding of Discus. There is limited knowledge on the genetic structure of its species complex and also the genetic basis of its stock constitution and management. Random Amplified Polymorphic DNA (RAPD) fingerprinting was used to assess the genetic diversity among four wild forms of Discus: Symphysodon discus (Heckel), S. aequiefasciata aequiefasciata (Wild green), S. a. axelrodi (Wild brown) and S. a. haraldi (Wild blue) and five cultivated varieties of Discus (Turquoise, Pigeon, Ghost, Cobalt and Solid Red). The Mann–Whitney U-test used in the comparisons among the inter-wild form, inter-cultivated variety and between wild form and cultivated variety similarity indices revealed that the gene pool of the cultivated varieties of Discus is smaller than that of the wild Discus forms. Unweighted pair–group method with arithmetic means (UPGMA) phenogram showed that the Heckel Discus ( S. discus) is genetically the most divergent in relation to the other three wild forms, being 2.89 times further in mean genetic distance from the other three wild forms (Wild green, blue and brown) than Wild green to the other two wild forms (Wild blue and brown). The cultivated varieties is 3.18 times genetically closer to the three S. aequiefasciata wild forms (Wild green, blue and brown) (mean genetic distance=0.033) than to S. discus (Heckel) (mean genetic distance=0.105). This suggests that the S. aequiefasciata wild form is the more likely genetic origin of the cultivated varieties. In addition, there is no distinct clustering of individuals from the same cultivated variety indicating the lack of a genetic basis for the present phenotypic classification of the cultivated varieties. Outcrossing with the wild forms especially, the Heckel Discus is recommended to increase the level of genetic variability in the cultivated varieties.