Vegetative rescue and cloning of Eucalyptus benthamii selected adult trees

Abstract

Eu calyptus benthanii presents great aptitude for cultivation in American continent, and due to its origin from western Sydney, NSW, Australia, is especially recommended for regions with cold climates and frequent frosts. Taking their optimal silvicultural performance into account, selected genotypes will certainly represent an excellent alternative for future plantations. The cloning of superior genotypes is accomplished by vegetative propagation of mature trees, and requires physiologically juvenile or rejuvenated material. Special techniques are necessary to reverse the juvenility and adult tree recovery and promote favorable growth and rooting conditions. In the specific case of Eucalyptus sp., the most common vegetative rescue method used by forestry companies to obtain shoots (i.e., propagules) is the coppicing of adult trees, a technique which provides excellent juvenile shoots, favoring the adventitious rooting in cuttings. Cloning techniques are required to vegetative rescue and germoplasm banks formation of selected trees. The present study aimed to evaluate the vegetative rescue after the selection of phenotypes with superior silvicultural characteristics to clone adult trees of E. benthamii, evaluating which technique presented the best cloning result. The cuttings from canopy branches, epicormic shoots from the first (lowest) canopy branches, shoots obtained from girdling and shoots from the pruning of canopy branches were submitted to micropropagation, cutting, and microcutting techniques for each shoot type. Among the key findings for vegetative rescue and cloning, the percentage of in vitro establishment of epicormic shoot (79.2 %), ex vitro rooting (75.0 %) and acclimatization (27.8 %) were suitable. The cuttings of sprouts from girdling stood out as having rooting (18.7 % from greenhouse and 14.3 % from mini-incubator) and acclimation (11.2 % from greenhouse and 9.0 % from mini-incubator). The others vegetative propagations techniques tested did not result in shoot survival, rooting or acclimation.