Coffea canephora is an important economic crop in Nigeria, however, little is known about the diversity inherent within, and the genetic relationship among coffee grown and conserved in the country. We examined the genetic diversity and relatedness among 48 Coffea genotypes which included: (a) C. arabica, C. abeokutae, C. liberica, and C. stenophylla, (b) 14 C. canephora accessions conserved in the germplasm of Cocoa Research Institute of Nigeria (CRIN), and (c) 30 farmercultivated genotypes collected from SouthWestern Nigeria. By analyzing 433048 single nucleotide polymorphisms (SNPs) identified through genotyping-by-sequencing we discovered that previous characterizations of C. canephora based on morphological data were inconclusive. Here, we established the correct number of C. canephora varieties present in the CRIN genebank which was four and not six as previously described based on morphological characters. We found three distinct diversity structures within the C. canephora genepool that were dominated by a single genetic group determined from passport descriptors to most likely be of Congolese (Democratic Republic of Congo) origin. High uniformity was also found among the farmer-cultivated accessions with 99% of them representing C. canephora var. Niaouli as their ancestral background. The analysis showed that the genetic base of coffee germplasm in Nigeria is narrow compared to the large genetic diversity of C. canephora. Therefore, broadening this genetic base through future acquisition and hybridization is imperative. However, the relatively high genetic differentiation (F ST estimate = 0.3037) Electronic supplementary material The online version of this article (

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 (LD 50 ) of M 1 V 1 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.

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