Genetic diversity and population structure of Trichilia emetica Vahl in western Kenya using ISSR markers

Abstract Land-use changes can reduce genetic variation and limit the ability of tropical trees to adapt to climate change. Trichilia emetica , a versatile tree of ecological and economic importance in Kenya, remains uncharacterized at the genetic level. This study determined the genetic diversity and population structure of T. emetica in western Kenya using 15 Inter-Simple Sequence Repeat (ISSR) markers. A total of 171 DNA fragments were amplified, of which 94.65% were polymorphic, revealing substantial genomic variability. Overall, gene diversity was moderate (He = 0.15; I = 0.22), with Nandi (0.24) and Kakamega (0.18) populations showing the highest diversity while Kisumu and Siaya had the least (0.10). Analysis of molecular variance (AMOVA) partitioned 65% of total variation within populations and 35% among populations (ΦST = 0.35, p < 0.001), indicating moderate differentiation and restricted but ongoing gene flow (Nm = 2.39). The six populations were clustered into three major genetic groups consistent with ecological gradients. This study establishes the first molecular baseline for T. emetica in Kenya and demonstrate that ecological heterogeneity may play a role in influencing its genetic structure. Conservation work should preserve the populations in Nandi and Kakamega while implementing enrichment and assisted regeneration in Siaya and Kisumu populations to reduce loss of genetic diversity.