Genetic diversity of Faidherbia albida (Del.) A. Chev collections held at the World Agroforestry Centre (ICRAF), Nairobi Kenya

Faidherbia albida (Del.) A. Chev is a tree species native to Africa and the Middle East. It is an important agro-silvo pastural species owing to its morphological and physiological dynamics that mediate improvement of soil structure and fertility while offering several other benefits to farmers and the environment. Key among these is its reverse phenology, a phenomenon that allows the tree to compete minimally with crops while providing a favorable microclimate for their growth. It is also a chief source of fodder, wood, medicine and nectar for apiculture in the dry season. Sustainable incorporation of F. albida in African farming systems will only be underpinned by proper management of its genetic resources. Molecular information has become indispensible in the contemporary management practices of agroforestry plant species. Genetic structure data is crucial in conservation, breeding and introduction. Faidherba albida accessions in ICRAF seed bank are not characterized and they are gradually losing viability. This study assessed the genetic diversity of seventeen Faidherbia albida provenances from 10 African countries by employing amplified fragment length polymorphism (AFLP) with an aim of providing crucial background genetic diversity information for in situ and ex situ management and utilization of the collections. Plant materials consisted of F. albida accessions held at World Agroforestry Centre (ICRAF) seed bank. Five primer sets (EcoRI-ACA/MseI-CAT, EcoRIACT/ MseI-CTC, ECoRI-AAG/MseI-CTT, ECoRI-ACC/MseI-CAT and ECoRI-AGC/MseICTC) that produced clear and scorable bands were utilized for the analysis. Fragments were resolved using the ABI 3730 DNA analyzer. A total of 676 bands ranging from 50 to 499 base pairs were produced. GenALEx 6.41 was employed to reveal partitioning of variation across the populations and to display molecular relationships among the populations. Genetic diversity estimates were computed using TFPGA software. EcoRI-ACT/MseI-CTC was the most informative of the five markers (mean PIC 0.24). The average percentage of polymorphic loci over all populations was 34 %. Collections from the Taveta (Kenya) provenance had the highest percentage of polymorphic loci (69.53 %) while those from Manapools (Zimbabwe) had the lowest percentage of polymorphic loci (13.46 %). The average heterozygosity ranged from 0.05- 0.28 with a mean of 0.17 across all the provenances. There was high and quite significant population differentiation among the populations (PhipT =0.583, p=0.01). Amova revealed that 58 % of the total molecular variation was partitioned among the populations while 42 % was within the populations. UPGMA clustering to a great extent reflected the geographical origins and similarity of the germplasm save for Bolgatonga (Ghana) and Bignona (Senegal) whose positions could explain the origin and evolutionary trends that have shaped the population structure and distribution of the species. The results show that the germplasm held at ICRAF seed bank is of low genetic variability with the Western and some of the Eastern Africa provenances having the highest diversity. These can be used as seed sources for introduction and domestication programs. More collections need to be done to cover the entire distribution range of this species to capture more diversity and enrich this genepool.

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