Genetic assignment, diversity, and divergence of naturalised Acacia saligna (Fabaceae) in Tigray, Ethiopia

Reliable morphological identification of genetic entities within the Acacia saligna (Labill.) H.L. Wendl. species complex is difficult due to its high phenotypic plasticity, but essential due to its extensive use and ongoing development as a multipurpose agroforestry species in many countries. Acacia saligna, introduced into Ethiopia as a conservation tree in the 1980s, is recognised as a valuable multipurpose tree for fodder, fuelwood, and timber. Phenotypic variation is high, but the genetic diversity in the naturalised resource is unknown. We assessed the level of genetic diversity contained within, and genetic divergence among, five naturalised populations of A. saligna in Tigray, northern Ethiopia. Additionally, we used a Bayesian analysis approach to assign individuals of unknown taxonomic affinity in Tigrinian populations to one or more of the five known genetic entities present across the species’ natural range in Western Australia. Results suggest that naturalised populations of A. saligna established in Tigray have moderate to high levels of allelic genetic diversity, and genetic divergence among populations is low to moderate. The majority of Tigrinian individuals were assigned to the north-western lindleyi genetic entity (75.75%) or to the lindleyi genetic entity (7.57%). Knowledge of locally available genetic diversity, combined with additional genetic resources from Australia, will help researchers establish provenance resource stands that can provide a sound basis for an improvement programme. The programme will produce a range of A. saligna types for different agroforestry systems and for adoption by the farming community and forestry companies, thus supporting livelihood improvement and rehabilitation of degraded landscapes.