ABSTRACT

Induced mutation is one of the prime methods used for the improvement of theagronomic traits of crops. The aim of this research was to evaluate the effect of different levels of X-ray radiation on the growth components and to detect DNA polymorphism in two accessions of Bambara groundnut (Vigna subterranea (L.) Verdc.). Seeds of Bambara groundnut accessions were arranged into five groups each into a paper envelope containing 50 seeds each. The first groups served as the control (untreated) whereas the other groups were bombarded with different doses of X-ray (0, 5, 10, 15 and 20 MGy) respectively. The experiment was set up in a randomized complete block design (RCBD) with three replicates. Seeds were sown and monitored for germination at 21 days after sowing. Growth parameters investigated include germination, plant height, number of leaves, number of branches and leaf area. Growth parameters were recorded at 2, 4, 6, 8 and 10 Weeks After planting (WAP).  The results obtained on germination percentage showed a gradual reduction as the doses increased. Higher doses reduced seed germination in the two accessions. The result on the plant height ranged from 25 cm to 30 cm. the lowest irradiation dose 5 MGy enhanced the plant height in the two Bambara accessions whereas the highest dose significant caused a decrease in the plant height. Also, there was a higher leaf number with plants that received the lowest dose of X-ray in the Bambara accessions. In the Red accession, 5 MGy had 96 leaf numbers whereas 114 were counted in the Milk-color accession at 10 WAP. The result obtained on the number of branches showed an increase in the number of branches at 5 MGy. In the Red accession, the highest number of branches (34) was counted under 5 MGy followed by 10 MGy (32) and then the control. However, in the milk-color accession, the maximum number of branches (33) was observed under the control followed by 5 MGy (31). Similarly, the result obtained on the leaf area was positively influenced by the lowest irradiation dose 5 MGy in the two Bambara accessions studied. Irradiation dose of 20 MGy significantly reduced the plant leaf area. Five (5) primers used in this study showed DNA polymorphism. Primer OPB 02, OPB 08, OPB 10 and OPB 20 were 100 % polymorphic while primer OPB 14 was 90 % polymorphic. A total of 59 bands were detected, 58 were polymorphic whereas 01 was monomorphic. The DNA banding patterns observed in the gel electrophoresis revealed the presence or absence of different bands with variations in their intensities as a result of the x ray exposures. Based on Jaccard’s coefficient of similarity values, the maximum similarity value (0.833) was observed between 5 MGy and 10 MGy in the milk color accession whereas the Red accession recorded similarity value of (0.883) between 10 MGy and 15 MGy. The result has revealed that X-ray changed the banding patterns of the DNA of the mutated seeds when compared with the controls, hence can be adopted in mutation breeding of Bambara groundnut. From the results of this study, exposing seeds of the two Bambara accessions to 5 MGy of X-ray enhanced the vegetative growth of the plants and could be employed in mutation breeding for improved agronomic qualities. This result has further confirmed the use of RAPD marker in the identification of mutagenic treated plants in mutation breeding.