The Frankincense tree (Boswellia sacra, Burseraceae) from Oman: ITS and ISSR analyses of genetic diversity and implications for conservation.

DNA sequences from the ITS region of the nuclear genome and Inter-Simple Sequence Repeat markers (ISSR) were used to estimate genetic diversity among and within populations of the Frankincense tree Boswellia sacra from Dhofar, Oman. This is a culturally and ecologically relevant species that is showing symptoms of decline due to anthropic factors and, possibly, global warming. ITS sequences were 511 bp long and showed low (6.4%) variation among geographically different populations. The four selected ISSR primers yielded 93 reproducible bands, of which 91 (97.9%) were polymorphic in the 97 individual profiles obtained. Total genetic diversity (HT) and average heterozygosity within populations (HS) resulted fairly low (0.22 and 0.136, respectively). The accession from Wadi Dowkah, an UNESCO world heritage site, showed the lowest level of genetic diversity (HE = 0.107), while the eastern populations from the Hasik area harboured a slightly greater amount of variation. Analysis of Molecular Variance showed that differentiation among populations was relatively high (38.1%), possibly due to the reduced gene flow between the largely isolated stands of Boswellia (Nm = 0.39). Genetic distances and AMOVA suggested a clear differentiation between the eastern and western coastal populations, while those from the internal area did not form a consistent group. For conservation, the eastern sites should be given priority as core populations harbouring significant amounts of allelic diversity. Reasons for reinforcing the more depauperated stands, such as Wadi Dowkah, with local plant material only or, alternatively, with the introduction of germplasm from genetically distinct stands are discussed.