Coffee is the second most valuable commodity exported by developing countries, and supports the livelihood of more than 75 million people. There are limitations to preference for established cultivars due to the autogamous nature of the crop thereby making improvements via conventional breeding of many years to produce a new cultivar difficult. Mutation breeding can overcome these obstacles. One of the first steps in mutation breeding is to determine radio-sensitivity so that optimal irradiation treatments can be determined. Three cultivars: Kents, Mundo novo and Geisha were sourced from the coffee germplasm collection at the Mambilla Plateau substation of the institute, Taraba State, Nigeria. The biological effect of the physical was studied in the selected cultivars of Coffea arabica after the rooted seedlings were treated with various doses of Gamma rays: 0, 5, 10, 15, 20 and 25 Gy. Success takes percentage and seedling vigour were used as measures of radio-sensitivity at 4 weeks after settings (WAS), 8, 12, and 16 WAS. The results showed that genotype of the cultivars and dosage of irradiation significantly influenced response to irradiation treatments (p < 0.05). The effect of the irradiation on treated cultivars was inversely proportional to the emergence of the success takes, plant height, root length, number of roots and number of leaves. The optimal mutation treatment (LD50) of M1V1 cuttings was in the range of 12 Gy in all the treated Arabica varieties an indication to buttress the narrow genetic base with reference to the similarity of their evolutionary trends. This work provides data on dose treatments for mutation induction in coffee, which may be exploited for coffee improvement.
Key words: Cultivars, autogamous, mutation, irradiation and genotypes.