Genetic Diversity and Strong Population Structure of Tallow Tree (Pentadesma butyracea) in Natural Stands of Bassila, Benin: Insights from Microsatellite Markers

Abstract

The main objective of this study was to assess whether genetic diversity within individual mother trees influences allelic diversity within Pentadesma butyracea stands. Eight microsatellite markers were assessed in 43 individuals from 15 mother trees belonging to three natural stands of Pentadesma butyracea (Manigri, Bakabaka and Pénessoulou). The results reveal moderate genetic diversity within stands and marked differentiation among them. Four loci (50%) were polymorphic in Manigri, and five (62.5%) in Bakabaka and Pénessoulou. Pent18 and Pent24 were the most discriminating markers (PIC up to 0.720). The mean number of alleles per locus ranged from 2.6 to 3, and the Shannon index remained below 1 (0.144–0.294). Expected heterozygosity was similar in Manigri (He = 0.477) and Bakabaka (0.488), and lower in Pénessoulou (0.403), where a heterozygote deficit was observed (Ho = 0.389; FIS = 0.035), whereas an excess was observed in Manigri (FIS = −0.209). Genetic distances among individuals from the same mother tree were generally low (0 to 0.914). Genetic differentiation was very high (FST = 0.619 to 0.685). Among-stand variability (DST = 54.4%) exceeded within-stand variability (He = 46%). Gene flow was very low (Nm = 0.076–0.101). Principal coordinate analysis (96.22%) distinguished two gene pools comprising individuals from all populations. UPGMA clustering of the 43 individuals defined three groups, one of which comprised 83% of individuals, originating from several mother trees and stands, some with zero genetic distance. These results provide key molecular tools and crucial genetic insights to optimize mother tree selection, guide reforestation programs, and prioritize in situ conservation of unique and fragmented gene pools of Pentadesma butyracea.