Testing New Provenances of Eucalyptus polybractea: A Eucalypt Oil Mallee Adapted to Semi-Arid Environments

Novel genetic accessions of Eucalyptus polybractea from a previously untested, hotter and drier part of the species’ natural range were tested in a common garden trial at a semi-arid site in NSW, Australia. Eucalyptus polybractea is a mallee eucalypt cultivated for essential oils (1,8-cineole), bioenergy and carbon sequestration on dryland sites in southern Australia (sites receiving about 450 mm mean annual rainfall, MAR). A trial of six previously untested provenances from the relatively hot, dry part of the species’ natural range in South Australia (SA) (250–450 mm MAR) was established alongside seven provenances from New South Wales (NSW) and Victoria within a commercial plantation in NSW. The trial was assessed at age 3.7 years for growth and oil characteristics. While survival was excellent, most of the SA sources were slower growing and of sub-standard oil concentration and quality relative to those from Victoria and NSW. However, a single SA provenance, with the highest oil concentration and 1,8-cineole percentage of all provenances tested, may have potential as a source of selected germplasm. Infusion of SA material into the breeding populations of E. polybractea, which are currently based on NSW and Victorian selections only, may provide more resilience in the face of hotter and drier temperatures expected under projected climate change scenarios, and/or allow the introduction of the species to hotter and drier climates in Australia or other parts of the world with semi-arid climates. However, high-intensity selection of infusions will be required to maintain the growth and oil characteristics in the existing breeding population.