ABSTRACT

 This research work was aimed at investigating the dosimetry of X-ray doses on three okra (Abelmoschus esculentus. L Moench) varieties (TAE38, Oboro dwarf and Okra hausa), the effects on different X-ray doses on the growth parameters and to detect DNA polymorphism among X-ray irradiated okra accessions through RAPD marker analysis. Seeds of the okra varieties were arranged into six groups each into a paper envelope containing 20 seeds each. The first group served as the control whereas the other groups were bombarded with different X-ray doses (1.0, 2.0, 4.0, 6.0 and 8.0 MGy) respectively. The genomic DNA of the fresh leaves of the plants was isolated using CTAb (Cetyltrimethylammonium Bromide) method for PCR-RAPD marker analysis. The results ofthe dosimetry test showed that 6 MGy recorded the optimum plant height curve on TAE. In Oboro dwarf, the optimum curve was observed on 6 MGy. In Okra hausa, the optimum plant height curve was observed on 8 MGy. From the dosimetry test result, two dose ranges were chosen for further investigation. The effects of irradiation doses showed a significant difference on the plant height at the early stage (3 WAP) of the plant growth in TAE38 and Okra hausa except in Oboro dwarf where the effect was not significantly different. At the later stages of growth (6 WAP and 9 WAP), the results obtained was not significantly different on the three varieties under study. The effects of the irradiation doses on the number of leaves per plant on TAE38 and Oboro dwarfwere not significantly different at 3 WAP, 6 WAP and 9 WAP respectively. In okra hausa, the results showed a significant difference at 3 WAP, 6 WAP and 9 WAP. The results ofthe analysis ofthe effects of X-ray doses on the number of branches showed that there was a none significant difference on TAE38 and Okra hausa. The effects ofthe X-ray doses on the number of branches in Oboro dwarf were significantly different. The results of the number of days to first flowering showed that there was significant difference on the three varieties under investigation. Application of X-ray irradiation induced changes in the banding patterns in the three okra varieties. The variations in the DNA profile in response to X-ray irradiation treatments were detected by RAPD-PCR technique. Three primers out five used for RAPA analysis showed polymorphism. Primer OPB-05 showed 100 % polymorphism, OPT-20 was 71 % polymorphic and primer OPH-05 showed 67 % polymorphism. A total of 21 bands were observed, 18 ofthese bands were polymorphic whereas 3 were monophorpic. Genetic similarity coefficient observed ranged from 0.333 to 0.888. A similarity coefficient was generated from the data obtained from the RAPD marker from the three okra varieties irradiated. A dendrogram or cluster tree analysis was constructed which showed the genetic relationship amongst the okra varieties as a result of the X-ray treatments. A higher genetic similarity (89.3 %) was observed between TAE38 6 MGy and Okra hausa 7 MGy. Also, Oboro dwarf 5 MGy and Oboro dwarf 6 MGy showed 89.3 % genetically similarity. The lowest genetic relationship was shown between TAE38 control and TAE38 5 MGy. This present work has shown that irradiating okra seeds with x-ray were effective in improving the plant growth. In this respect, X-irradiation by 5 MGy and 7 MGy respective gave the highest effects. Also, DNA polymorphism detected by RAPD marker offered a useful molecular marker for the identification of mutagenic treated plants.