ABSTRACT

Assessment of genetic diversity is an essential component in germplasm characterization and utilization. Therefore, a study was undertaken to investigate the morphological and molecular characterization for assessment of genetic diversity of some sweetpotato accessions in Nigeria. Evaluation of the sweetpotato germplasm was carried out under rain-fed conditions using Randomized Completely Block Design (RCBD) with three replications at the Teaching and Research Farm of the Federal University of Technology, Owerri (FUTO) and at the National Root Crops Research Institute (NRCRI) Potato Programme, Kuru, Jos, Plateau State, North Central Nigeria during the 2018 cropping season. The molecular characterization was carried out at the Molecular laboratory of the Godfrey Okoye University, Enugu State in 2019. Thirty sweetpotato seeds were obtained from International Potato Center, Kumasi, Ghana, Mozambique and local germplasm of the National Root Crops Research Institute (NRCRI), Umudike, Umuahia, Abia State in Nigeria as well as sweetpotato vines from local farmers’ fields in Jos, Plateau State and Bauchi, in Bauchi State, Nigeria. These were investigated using Morphological and Molecular characterization approaches. The attributes for morphological, agronomic and nutritional characters were used to identify variations among the accessions. The results revealed that significant differences existed among the accessions (P<0.05) for the morphological and agronomic characters investigated. The first ten principal components with coefficient values greater than 1.0 together accounted for 97.68% of the total variation. Significant positive correlation was found between predominant flesh colour and storage root shape (r=0.722**, p<0.01), and also between predominant skin colour and mature leaf colour (r=0.831**, p<0.01). Total storage root yield had positive correlation with number of marketable roots, (r=0.788**, p<0.01), marketable weight/ha (r=0.99**, p<0.01) and unmarketable weight/ha (r=0.241*, p<0.05) but negative correlation with number of unmarketable roots, (r=-0.282, p<0.01). Cluster analysis based on the Unweighted Paired Grouped Arithmetic Average (UPGMA) grouped the accessions into three clusters for the morphological characters and four clusters for the molecular characters. Five Simple Sequence Repeats (SSR) primers used for the study detected polymorphism among the sweetpotato accessions. The primers detected a total of 18 alleles and the number of alleles per locus was 4 for IBR-19, IBR-286, IBR-297 and 3 for IBR-16 and IBR-242 with an average of 3.67 alleles per locus. The polymorphic information content (PIC) of the markers varied from 0.35 to 0.72 with an average of 0.497. Marker IBR-19 revealed the highest PIC of 0.72, while marker IBR-297 had the lowest PIC of 0.35. Observed heterozygosity ranged from 0.32 to 0.89 with a mean of 0.675 across the five SSR loci. Based on the genetic distances resulting from the analysis of the dendrogram for the combined morphological and molecular characters and also from the agronomic and nutritional characterization, twenty accessions were selected for in vitro and ex situ conservation and as core collection for future breeding and other agronomic programmes.