Abstract
ABSTRACT This study aims to evaluate the effect of IBA concentrations and microcuttings successive collections in the micropropagation of Eucalyptus grandis x E. urophylla and Eucalyptus urophylla x E. globulus clones. Clumps containing six to eight buds of clones established in vitro were transferred to a 250 mL glass flask in JADS semisolid medium. Successive collections were performed every 20 days for Eucalyptus grandis x E. urophylla clone and every 30 days for Eucalyptus urophylla x E. globulus clone. The following variables were evaluated under in vitro conditions: number of shoots > 0.5 cm, number of microcuttings > 2 cm, length of the longest microcutting, and shoots vigor. Under ex vitro conditions, in the greenhouse and shade house, the following variables were evaluated: seedling height, percentage of survival, stem diameter, percentage of root observed at the lower end of the tube, and seedling vigor. In full sun (ex vitro), the following variables were analyzed: seedling height, stem diameter, survival, number of roots, root volume, seedling vigor, and shoot and root dry matter. Good in vitro microcuttings productivity was observed over the successive collections. IBA levels were adjusted for each clone, ranging from 0.25 to 0.50 mg L-1 for Eucalyptus grandis x E. urophylla clone, and from 0.75 to 1.0 mg L-1 for Eucalyptus urophylla x E. globulus clone. IBA concentrations led to residual effects under ex vitro conditions, providing good rooting and survival for Eucalyptus grandis x E. urophylla and Eucalyptus urophylla x E. globulus clones at IBA concentrations between 0.25 and 0.50 mg L-1 and between 0.50 and 1.0 mg L-1, respectively.
Highlights
This study aims to evaluate the effect of indole butyric acid (IBA) concentrations and microcuttings successive collections in the micropropagation of Eucalyptus grandis x E. urophylla and Eucalyptus urophylla x E. globulus clones
IBA levels were adjusted for each clone, ranging from 0.25 to 0.50 mg L-1 for Eucalyptus grandis x E. urophylla clone, and from 0.75 to 1.0 mg L-1 for Eucalyptus urophylla x E. globulus clone
IBA concentrations led to residual effects under ex vitro conditions, providing good rooting and survival for Eucalyptus grandis x E. urophylla and Eucalyptus urophylla x E. globulus clones at IBA concentrations between 0.25 and 0.50 mg L-1 and between 0.50 and 1.0 mg L-1, respectively
Summary
The successful productivity of Eucalyptus plantations in Brazil is a result of the combination of several factors, such as the well-established clonal forestry programs, the constant development of genetic improvement strategies, the production of specific hybrids, the selection of elite clones, and the improvement of clonal propagation technologies (Ferrari et al, 2004; Xavier et al, 2013).Micropropagation is a clonal technique that produces microcuttings and provides countless advantages to the production process of Eucalyptus seedlings, such as faster mass propagation of clones; greater nutritional, environmental, and phytosanitary control; and longer storage periods; besides retention of hybrid vigor and the possibility of transport over long distances without damaging the material (Bisht et al, 1999; Xavier et al, 2013).In addition, microcuttings production by micropropagation improves the cloning process due to the rejuvenation and reinvigoration technique used as a mechanism to overcome rooting problems of the cuttings, which is mainly observed in the rescue of adult trees (Joshi et al, 2003; Xavier et al, 2013).Specific innovations have been proposed for the application of large-scale micropropagation technologies in Eucalyptus (Xavier et al, 2013), such as the manipulation of the in vitro atmosphere and/or environment (e.g., photoautotrophic propagation) (Kozai, 2010); the use of temporary immersion and liquid medium bioreactors (Oliveira et al, 2011, 2014); the replacement of the semisolid medium with alternative substrates (Kirdmanee, et al, 1995); the automation and mechanization of systems operations (Penchel et al, 2007); and the use of in vitro microclonal hedge.Several factor can influence the productivity of the traditional miniclonal hedge, such as climatic variables, the genetic material, the production system (Cunha et al, 2005), the mineral nutrition (Cunha et al, 2009a), Revista Árvore. 2017;41(6):e410605 the management of miniclonal hedge seedlings (Mafia et al, 2005), among others. The successful productivity of Eucalyptus plantations in Brazil is a result of the combination of several factors, such as the well-established clonal forestry programs, the constant development of genetic improvement strategies, the production of specific hybrids, the selection of elite clones, and the improvement of clonal propagation technologies (Ferrari et al, 2004; Xavier et al, 2013). Micropropagation is a clonal technique that produces microcuttings and provides countless advantages to the production process of Eucalyptus seedlings, such as faster mass propagation of clones; greater nutritional, environmental, and phytosanitary control; and longer storage periods; besides retention of hybrid vigor and the possibility of transport over long distances without damaging the material (Bisht et al, 1999; Xavier et al, 2013). Cunha et al (2009b) concluded that the increase in temperature favors the production of minicuttings in eucalyptus miniclonal hedge, regardless of the miniclonal hedge type
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