Tracing the genetic origin of two Acacia mearnsii seed orchards in South Africa

The aims of this investigation were to assess the genetic origin of two black wattle seed orchards at molecular levels and to determine genetic diversity within and among the A. mearnsii provenances planted in Southern Mpumalanga, South Africa using a reference population. The method used for sample collection, DNA extraction, PCR and genetic analysis followed the protocol developed in our laboratories for Acacia mearnsii. The overall mean alleles per locus was 8.8 among all A. mearnsii individuals; the highest number of allele was 14.0 for primer AH3-10 and the least was 3.0. for AH3-1 and AH16. The Potgieterskues provenance revealed the highest genetic diversity (He = 0.59), allelic richness (Ar = 5.78) and total number of private alleles (PA = 15), whereas Mittagong showed the lowest He = 0.50 and Ar = 4.42. An unweighted pair group method with Neighbour-joining cluster analysis and Bayesian STRUCTURE analysis, based on allele profiles of 11 microsatellite loci, separated the 281 individual trees into three distinct genetic clusters. The clustering of the samples did not strictly follow the geographic origin of individuals. Both the AMOVA and STRUCTURE analysis revealed the distinctiveness of the Potgieterskues stands with 36% of the trees related to Sheepmoor, Mittagong and Lake George provenances. The Sheepmoor, Mittagong and Lake George provenance largely grouped into the same genetic cluster with no significant genetic differentiation. The relatively larger number of unique allele from the Potgieterskues stand suggest that seed unknown to the ICFR was used to establish the orchard. Using assignment score > 95% as criteria, it was possible to trace the genetic origin of some of the trees in the Sheepmoor orchard. This work is the first of its kind for the South African wattle industry. It will provide the foundation for DNA-based molecular support to the breeding programmes.