Molecular Characterization of Sclerocarya birrea ICRAF Field Genebank Collections

Abstract

Scelerocarya birrea is an important fruit tree that is widely used by the rural populations in most regions in which it is found, for its fruits, bark, timber and even its roots. The local communities harvest the tree products from the wild with minimal attempts to grow it on-farm. The sustainability of such wild harvests is threatened by agriculture, overgrazing and overexploitation for other purposes. Therefore, the species needs urgent conservation measures in addition to selecting superior germplasm for on-farm tree management that will facilitate ease of species cultivation. This has prompted the International Center for Research in Agroforestry (ICRAF) and partners to collect and manage S. birrea germplasm in field genebanks as the initial step towards the species domestication and conservation. In order to effectively manage germplasm, it is important to establish the collection genetic diversity. Six ISSR markers yielded a total of 76 polymorphic bands across the 257 accessions studied. Percentage of polymorphic loci and observed heterozygosity ranged from 75% to 7.89% and H=0.362 to H=0.043, respectively. The partitioning of genetic diversity found a higher (86% P>0.001) intra-population variation and low inter-population variation, typical of the outcrossing nature of S. birrea. According to Jaccard’s dissimilarity index, the highest genetic distance between accessions was 1.000 and the least genetic distance was 0.000. Neighbour-joining clustering grouped the accessions into three major clusters and twenty probable duplicates were identified, which should be eliminated to cut down the cost of conservation. The results obtained suggest that S. birrea ICRAF field genebank collections have a comparatively rich gene pool and, hence, valuable for conservation of S. birrea. The twenty samples showing duplicates would be good for evaluating performance of this long-lived tree species in both locations.