Effect of light intensity and seal type on the in vitro elongation and adventitious rooting of Eucalyptus grandis × E. urophylla

Background: Rejuvenation/reinvigoration of tissues through micropropagation has become an important tool for clonal propagation in eucalypts species. This study evaluated the effect of photomixotrophism (i.e., light intensity and seal type) on in vitro elongation and adventitious rooting to identify the limiting factors on in vitro culture of the Eucalyptus grandis × E. urophylla hybrid. Methods: Nodal segments (i.e., explants) from ministumps grown in a semi-hydroponic system were collected. The effects of light intensity and seal type on in vitro elongation and adventitious rooting stages were evaluated from a 40 μmol m-2 s-1 fluorescent lamp and 20, 40, and 80 μmol m-2 s-1 red/blue LEDs, with (through porous membranes) and without gas exchange. Results: Based on the results at 35 d, 40 μmol m-2 s-1 fluorescent lamp and gas exchange combination was the most suitable for in vitro elongation and adventitious rooting of Eucalyptus grandis × E. urophylla. Both factors increased the vigour, shoot length, photosynthetic pigment content, xylem, phloem, stomatal number and density, root length, diameter, number of roots per explant, and adventitious rooting fraction. Conclusions: Light intensity and seal type influences the in vitro elongation and adventitious rooting of Eucalyptus grandis × E. urophylla. The results contribute to optimising the cloning of commercial eucalypts species by the micropropagation technique.