GENETIC DIVERSITY OF Celtis zenkeri ENGL IN SOUTH WEST NIGERIA

Abstract

This study assessed the impact of anthropogenic activities on the genetic diversity of Celtis zenkeri (Ulmaceae) in South West Nigeria. Celtis zenkeri is a valuable tropical tree species for industrial and domestic functions. The stems are easily worked upon by wood workers while the leaves are mainly used for food, trado-medical and agroforestry purposes. For several years, exploitation has been heavily carried out on this important tree species without reforestation effort. Therefore, this study was carried out to investigate the impact of anthropogenic activities on the genetic diversity of Celtis zenkeri in South West Nigeria. A reconnaissance survey was carried out to identify the mature trees of Celtis zenkeri. In this study, four natural populations [two pristine forests (Queens’ Plot, Akure Forest Reserve and Osun Osogbo Sacred Grove) and two degraded forests (Oluwa Forest Reserve, OA3 series, and Eda Forest Reserve)] where Celtis zenkeri could be found were purposively selected. Complete enumeration of Celtis zenkeri were carried out, two young leaves were collected from each tree found in each location and their GPS coordinate were also recorded. In all, 130 accessions were sampled and were analyzed with five chloroplast microsatellite markers. The allelic richness (Ar), which is a measure of genetic diversity and an indicative of a population's long-term potential for adaptability and persistence, was significantly higher in the two pristine forests [Queens’ Plot, Akure Forest Reserve (Ar 6.20) and Osun Osogbo Sacred Grove (Ar 5.60)] than the two degraded forests [Oluwa Forest Reserve, OA3 series (Ar 5.00 and Eda Forest Reserve (Ar 3.60)]. The observed heterozygosity recorded for the two pristine forests [Queens’ Plot, Akure Forest Reserve (Ho 0.09) and Osun Osogbo Sacred Grove (Ho 0.13)] were not significantly different from a degraded forest [Oluwa Forest Reserve, OA3 series (Ho 0.09)]. Also, the expected heterozygosity, the probability that two gametes randomly chosen from the gene pool are of different alleles, was significantly higher in a pristine forest [Queen’s Plot, Akure 3 Forest Reserve (0.78)] and a degraded forest [Oluwa Forest Reserve, OA3 series (0.78)]. Generally, the allelic richness, observed and expected heterozygosity were significantly low in the degraded forest. Anthropogenic activities, which may cause inbreeding and inbreeding depression, had negatively impacted the genetic diversity of Celtis zenkeri in Eda Forest Reserve. The results obtained for the degraded forests could be traced to the level of anthropogenic activities and unsustainable timber harvesting. It is therefore recommended that conservation measure be put in place by the government to ensure high genetic diversity of important tree species threatened with extinction.