Genetic diversity, Species Niche Modelling and Ethnobotanical uses of Strychnos henningsii for Sustainable Conservation and Utilization

Abstract

Strychnos henningsii (Gilg.) belongs to the family Loganiaceae. It is a narrow endemic and endangered medicinal plant species largely confined to the dry land parts of Kenya. It is highly over exploited for medicinal purposes, which has resulted in its decline in the natural habitats. A research study was therefore undertaken to determine the genetic diversity, species niche modeling and ethnobotany of Strychnos henningsii in order to come up with strategies for its conservation, cultivation and sustainable utilization. Genetic diversity study of two hundred and seventy individuals sampled from nine populations of Strychnos henningsii in Kenya was carried out using RAPD and ISSR markers.This was undertaken to determine the genetic variation within and among its populations and recommend those that revealed sufficient genetic variation as the best sources of the planting materials. Ten RAPD and nine ISSR primers were selected from forty RAPD and ISSR markers screened for the study. The mean percentage polymorphism detected was 38.97 % for RAPD and 43.40 % for ISSR markers. The mean values of Shannon information index (I) and genetic diversity (H) showed by these primers were 0.3310, 0.2005 (RAPD) and 0.4473, 0.2889 (ISSR) indicating low genetic variability among .S. henningsii genotypes. The similarity coefficient based on the Nei’s unbiased genetic distance revealed low level of divergence among the different populations of S. henningsii. The values ranged from 0.8422 to 0.9796 (RAPD) and 0.7239 to 0.8803 (ISSR) AMOVA analysis revealed high genetic variation among populations than within populations ie 54 % and 46 % (p>0.001) respectively for RAPD and 58 % and 41 % (p>0.001) for ISSR analysis. Low genetic diversity could be attributed to the self pollination mechanism in S. henningsii. Therefore, conservation efforts should aim to preserve all the extant populations of this threatened species. The potential suitable habitats for growth and conservation of this species in Kenya were determined using maxEnt modeling method. MaxEnt performance in delineating the potential distribution areas of S. henningsii in Kenya was good and reliable. The area under the ROC curve (AUC) indicated the values for training and test data were 0.986 and 0.983 respectively. These values were close to 1 thereby showing the accuracy of the model in prediction. The predicted areas were Taita hills, shimba hills, Kilifi (Arabuko sokoke forest), Mt Kilimanjaro game reserve), Marsabit, Huri hills, Marigat, Baragoi, Malaral (dryland areas in Kenya), Ngong and Karura forests. These aera could be targeted for conservation of S. henningsii. Ethnobotanical study was conducted on Strychnos henningsii to determine the traditional knowledge of this species by the local people using semi structured questionnaires to collect the data. The study showed clearly that Strychnos henningsii a wide range of uses in all the areas of study and that majority of the respondents (50 %) obtained the plant species with lot of difficulty. The key difficulties identified were scarcity (29 %) and long distance walking (35 %) indicating the decline of this species in its natural habitats. Of all the persons interviewed sixty eight percent did not grow Strychnos henningsii in their farms while ninety eight percent collected their plant materials from the forests. The results also indicated that the roots (43 %) and stem (47 %) were the most frequently used plant parts for medicinal purposes and often crude methods which are destructive to this species are employed to collect the plant materials. The respondents suggested that training them on proper harvesting methods (32 %), establishment of nurseries (23 %) and planting this species locally (33 %) would be some of the ways to overcome the difficulties experienced while dealing with not only this species but also many other medicinal plant species.