MORPHOLOGIC AND MOLECULAR CHARACTERISATION OF Ricinodendron heudelotii (Baill.) Pierre ex Pax IN SOUTHERN NIGERIA

Abstract

Ricinodendron heudelotii is an ethnomedicinally important indigenous tree species found in wild populations in Nigeria, but its utilisation is limited by insufficient taxonomic information. Morphologic and genetic characterisations provide detailed taxonomic description for effective identification of indigenous tree species. However, such information is scarce with respect to Ricinodendron heudelotii in Southern Nigeria. Therefore, morphology and molecular characteristics of leaf and fruit of Ricinodendron heudelotii trees in Southern Nigeria were investigated. Wild Ricinodendron heudelotii trees were purposively selected from Oyo [Ibadan (n=1) and Onigambari (n=5)], Ondo [Oloruntele (n=12) and Akure (n=4)], Osun [Osu (n=8), Ikoyi (n=4) and Ile-Ife (n=10)], Edo [Benin (n=4)] and Cross River [Boki (n=2)] States, based on availability. Fifty random samples of uniformly sized leaves, from each location, were assessed for Leaf Length (LL, cm), Petiole Length (PL, cm), epidermal cell shape, Guard Cell Area (GCA, µm2), Pore Size (PS, µm2), Stomata Length (SL, µm) and epidermal cell length (ECL, µm) following standard methods. For fruit and seed morphology, 50 matured fruits were randomly collected from each location and used to determine Fruit Length (FL, mm), Pulp Weight (PW, g), Fruit Largest Width (FLW, mm), Fruit Roundness Ratio (FRR), seed length (mm) and Seed Diameter (SD, mm2) using standard procedures. Six leaves from each location were subjected to molecular characterisation using 19 Inter Simple Sequence Repeat (ISSR) markers following standard methods. Polymorphic Information Content (PIC), genetic diversity, similarity index, and unique allele were determined. Data were analysed using descriptive statistics, Principal Component Analysis (PCA), Cluster Analysis and ANOVA at α0.05. Leaf length significantly increased from 22.3±5.7 (Osu) to 53.0±5.8 (Onigambari), while PL varied from 8.9±0.1 (Boki) to 30.9±5.0 (Onigambari). Epidermal cells were polygonal in all sites, except Akure with irregular shape. Highest GCA (243.1±30.5), PS (322.8±78.5), SL (29.4±2.4) and ECL (43.7±8.8) were in Akure, while the least were in Ikoyi (72.7±7.0), Onigambari (40.3±8.0), Ikoyi (20.4±3.6) and Ibadan (19.2±8.7), respectively. Boki had highest (45.4±2.6) FL, while Ile-Ife had least (30.2±11.5). The PW and FLW were highest at Oloruntele (34.3±7.2; 44.2±4.0) and least at Akure (18.4±3.3; 31.2±1.3). The FRR and seed length varied from Oloruntele (14.4±1.7; 0.77±0.3) to Akure (17.1±0.7; 1.31±0.11), while SD ranged from 12.9±0.9 (Akure) to 16.3±0.6 (Ile-Ife). The GCA (0.48), PS (0.57) and SL (0.39) had highest contribution to the 76.8% total variance in leaf and fruit morphometrics. The ISSR marker-840 had highest PIC (0.42), while ISSR marker-848 had the least (0.21). Genetic diversity increased from Akure (0.09) to Oloruntele (0.24). Highest genetic similarity (60.3%) was between Ibadan and Osu, while the least (1.0%) was between Akure and Benin. Three unique allele (1600-2000bp) were identified in Oloruntele. The population of Ricinodendron heudelotii clustered into four groups; Akure, Benin and Oloruntele were distinct, while others formed a group. Leaf-based characters showed distinct taxonomic differences across populations of Ricinodendron heudelotii in Southern Nigeria. The most genetically diverse population was found in Oloruntele, which indicates potential germplasm for domestication of the species. The unique alleles identified could be used for marker assisted identification of the population.