Occurrence of polyploidy in populations of Acacia dealbata in south-eastern Tasmania and cytotypic variation in reproductive traits

The frequency of polyploid trees in 10 populations of the predominantly diploid species Acacia dealbata subsp. dealbata Link in south-eastern Tasmania was determined using flow cytometry. At seven of the sites, all trees were diploid. At two sites, single triploid genets were found and, at a third, two tetraploids. Microsatellite markers were used to confirm that triploid trees distributed over an area of at least 930 m² at the major study site were all ramets of a single genet. Three diploid clones were also confirmed at this site. The 16-grain polyads from the triploid genet were significantly larger than those from diploids, but only the diploid pollen showed any viability in vitro. At three months the green pods on diploids averaged 36 mm and contained four developing seeds per pod. Pods on the triploid were only 13 mm long, with no developing seeds. In spite of maturing pods, two of the diploids did not yield full seed, whereas two other diploids averaged only 0.1 seeds per pod. Seeds were not produced on triploid trees. The low reproductive output is discussed with reference to the breeding system and the impact of clonality on effective cross-pollination.