Genetic Diversity of Vernonia Schreb. Species in Nigeria
Vernonia Schreb. is a genus in the family Asteraceae. It has over 1000 species which may be trees, shrubs, woody climbers or herbs. Some of the species are economically important as sources of food and herbal medicine as well as for industrial purposes. Despite the economic importance of the species, the existing taxonomic and phylogenetic relationships among the taxa are not totally resolved. The objective of this study was to assess the genetic diversity of Vernonia species in Nigeria using in-situ morpho-genetic characterization, leaf epidermal micromorphology and molecular characterizations as well as geo-spatial modeling approaches.In–situ morphological characterization was carried out on 61 field samples consisting of 14 Vernonia species collected from Nigeria. Light microscopic studies of the foliar epidermal micromorphology were undertaken on the 14 Vernonia species from field collections with a view to elucidating the taxonomic significance of the epidermal features. The characters were analyzed to determine the variations which may be useful in species identification. Molecular characterization was carried out with a total of 50 Vernonia samples consisting of 34 samples (13 species) from field collections and 16 samples (10 species) from Ife Herbarium collections making a total of 23 species using 34 RAPD primers. Analysis of the molecular data was done using NTsys version 2.02j computer programme. GIS methods were employed for the geospatial data analysis of the samples using ARC GIS 10.1 in which Arc Catalogue and Arc Map were embedded. Geo-spatial data were used to generate a species distribution model (SDM) for Vernonia species. Qualitative and quantitative assessment of epidermal characteristics revealed diagnostic features such as anomocytic stomatal type found on amphistomatic and hypostomatic leaves. Mean stomata index ranged from 1.06 % - 22.22 % in the genus. The epidermal cell shape was mostly polygonal or sinuous on both surfaces or polygonal or sinuous on either surface. Anticlinal wall pattern was straight or undulate on both surfaces or straight/curved or undulate on either surface, as well as wavy or undulate on either surface. Multicellular and other trichomes which manifested various geometrical forms were also observed. Results from molecular studies showed amplification through polymerase chain reaction (PCR) with 4 RAPD primers namely OPA-02, OPD-14, OPC-10 and OPE-01. Analysis of the molecular data grouped the samples into 4 Clades with only one species ungrouped. Clades I had 17 species, II had 3 species, III had 6 species and IV had 2 species. V. amygdalina was represented in all 4 Clades, V. glabra and V. guineense were present in Clades 1 and 3, V. tenoreana and V. purpurea were in Clades 1 and 2 respectively, while V. colorata remained ungrouped. All 50 Vernonia samples used in the molecular study clustered at 64%. Phylogenetic analysis using combined data from morphological, leaf epidermal and molecular studies showed relationship among the 12 Vernonia taxa studied at these levels and grouped them into 4 Clades. Results obtained from in-situ morphogenetic studies of the 61 field Vernonia samples were used to construct dendrograms using unweighted pair group method with arithmetic average (UPGMA) clustering which showed the phenetic relationship amongthe accessions studied. Principal Components Analysis (PCA) revealed that leaf characters were important botanical marker traits with a large coefficient of variation (>51%) which most effectively discriminated theVernonia accessions andwas therefore used in establishing a simple but effective Vernonia classification system in Nigeria. The results of this study will be useful in the identification, classification, conservation, management and sustainable use of the species.SDM appeared to be clustered in space within the sampling areas through Nearest Neighbour Index (NNI) at a Z score of < - 2.58 and p = 0.01.