Diversity Analysis of Sweet Potato (Ipomoea batatas [L.] lam) Accessions from North Central Nigeria Using Morphological and Simple Sequence Repeats Markers

Aims: Genetic diversity analysis was carried out with the aim of assessing the genetic similarities and variability that existed among sweet potato accessions that are grown in North Central Nigeria using Morphological and Simple Sequence Repeats makers.

Study Design: The field experiment was laid out in a Randomized Complete Block design (RCB) with 5 replications. Morphological characterization was done in the field while Molecular characterization was carried out in the Molecular laboratory.

Place and Duration of Study: Field experiment was carried out at the Teaching and Research farm of the Federal University of Agriculture Makurdi while the laboratory experiment was done at the Molecular Biology laboratory of the Federal University of Agriculture Makurdi. The experiment was carried out between May and August 2018.

Methodology: A total of 20 potato accessions collected from six states (Benue, Kogi, Nasarawa, Niger, Plateau and Abuja) in north central Nigeria were planted in the field for morphological characterization and Observations were made on 21 morphological characters at 90 days after planting (DAP). Genomic DNA for molecular characterization was extracted from young leaves (20 DAP) located at the tip of the main vine of the sweet potato plant using DNA Zol extraction protocol. The extracted DNA was amplified using five SSR primers via Polymerase Chain Reaction in a thermocycler. The amplified DNA was then subjected to 5% Agarose gel electrophoresis and the products were viewed under U-V light. The bands formed as a result of amplification were scored in a binary pattern for analysis.

Results: ANOVA of the of morphological characters revealed that there were significant variation for 18 out of the 21 morphological characters studied among the sweet potato accessions, with the first 4 Principal Components accounting for 72.1% of the total variations among the accessions. The 18 characters were thus useful as morphological markers for diversity analysis and based on them, cluster analysis grouped the sweet potato accessions into 4 clusters based on their average linkages and the Euclidean test. Four pairs of duplicates (NC 7 and NC 15, NC 8 and NC 16, NC 17 and NC 19, NC 18 and NC 20) were identified to be similar accessions based on the morphological characterization. For molecular characterization, Polymorphic Information Content (PIC) for the DNA bands formed showed the usefulness of the primers used in revealing genetic diversity among the accessions with primer 1 (IB02) and 4 (IBS 199) showing 31.818% polymorphism in 1 (IB02) and 4 (IBS 199). For cluster analysis, three distinct clusters were observed with all the accessions in cluster I and II which were approximately 30% similar while accession NC 10 which stood alone in cluster III shared no similarity with any of the other accessions and could possibly be a hybrid. The cluster analysis also revealed a total of 4 sets of duplicates thereby further reducing the total number of accessions to 6 which indicated that a very low diversity existed among the accessions.

Conclusion: This study established that a lot of duplicates existed among the sweet potato accessions indicating that there is a very low level of sweet potato genetic diversity in the North Central region of Nigeria.