ABSTRACT

There is a paucity of eucalypt species in tropical Australia that produce a foliar essential oil in high concentration and rich in 1,8-cineole, the sought-after component of medicinal eucalyptus oils. Eucalyptus bakeri, a mallee from the dry subtropical parts of northern New South Wales and Queensland, is an exception, with limited earlier studies reporting that this species produced foliar oil with commercial characteristics. The aim of this study was to determine the variation in foliar oil characteristics throughout the natural range of E. bakeri as a precursor to the more intensive field-testing of the species as a commercial source of eucalyptus oil. Mature leaves and, when available, coppice leaves for comparison were collected over three separate field trips in 2020 from individual trees representing each of 17 provenances throughout the natural range of E. bakeri in Queensland. Foliar oil concentrations on a fresh-weight basis throughout the provenances sampled were relatively high, averaging 2.3% for mature leaves and 2.8% for coppice leaves, with an individual tree high of 4.1% for both leaf categories. 1,8-Cineole was the dominant compound in all foliar oils sampled, averaging 89.3% (range 70.2–94.6%) in oils from mature leaves and 87.6% (range 79–92.5%) from coppice leaves. Sabinene levels, restricted to a maximum of 0.3% in some oil standards, averaged 0.3% (range trace – 1.5%) in oils from mature leaves and 0.4% (range trace – 0.7%) from coppice leaves. The high foliar oil concentrations and consistency in oil qualities mark this species as a potential candidate as a eucalyptus oil source species for the dry subtropics. Provenance/progeny trials are now needed to determine which provenances produce adequate growth rates and the silviculture required to manage the species as an oil-producing crop, as well as to investigate variations in oil characteristics, including sabinene levels, when all sources are grown at a common site.

摘要

澳大利亚热带地区的桉树种类很少，它们产生的叶面精油浓度很高，富含 1,8-桉树脑，这是药用桉树油中广受欢迎的成分。Eucalyptus bakeri是一种来自新南威尔士州北部和昆士兰州干燥亚热带地区的木槌，是一个例外，有限的早期研究报告说，该物种生产具有商业特征的叶面油。本研究的目的是确定E. bakeri整个自然范围内叶油特性的变化作为桉树油的商业来源，对该物种进行更深入的现场测试的先驱。在 2020 年的三个单独的实地考察中，从代表E. bakeri自然范围内 17 个种源中的每一个的单棵树中收集成熟的叶子和（如果有的话）用于比较的矮林叶在昆士兰。在整个取样的种源中，以鲜重计的叶油浓度相对较高，成熟叶平均为 2.3%，矮林叶平均为 2.8%，两种叶类的单棵树高 4.1%。1,8-桉树脑是所有采样叶油中的主要化合物，成熟叶油中的平均含量为 89.3%（范围 70.2-94.6%），矮林叶油中的含量为 87.6%（范围 79-92.5%）。在某些油标准中，桧烯的含量最高限制为 0.3%，成熟叶油中的平均含量为 0.3%（范围痕量 - 1.5%），而灌木叶油中的含量平均为 0.4%（范围痕量 - 0.7%）。高叶油浓度和油质的一致性标志着该物种作为干燥亚热带桉树油源物种的潜在候选者。