Artificial light improves productivity of mini-cuttings in a clonal minigarden of Eucalyptus benthamii and E. dunnii

Eucalypts are economically important worldwide, being largely propagated by clonal means, that is, frequently achieved by mini-cuttings. Regional climatic conditions, however, interfere with this strategy. Southern Brazil, especially in higher altitudes, has a considerable number of cloudy and cold days annually. It is a challenge for clonal propagation, even for cold-tolerant species such as Eucalyptus benthami and E. dunnii. The supplementation with artificial light has proved to be effective for improving growth in agricultural crops, but little work has been done with trees. Here we conducted a set of experiments for producing mini-cuttings of two commercial clones of E. benthamii and one clone of E. dunnii under the supplementation with artificial light, using red/far-red (660:730 nm) and red/blue (660:450 nm) light emitting diodes (LED), in comparison to a control (sunlight only). The supplementation with red/far-red and red/blue light increased the production of mini-cuttings in colder months, but more consistently positive impacts were observed with red/far-red lamps. The shoots produced under red/far-red light were more elongated and implicated in higher leaf canopy coverage. Overall, this work is a first step aimed at improving clonal propagation systems of E. benthamii and E. dunnii through mini-cuttings supplemented with artificial light.