Micropropagation of an Eucalyptus hybrid (Eucalyptus benthamii x Eucalyptus dunnii)

Abstract

ABSTRACT. This study was designed to micropropagate E. benthamii x E. dunnii, by testing chlorine concentrations for explant asepsis, the optimal concentrations of benzylaminopurine (BAP) and naphthaleneacetic acid (NAA) for bud proliferation, and the ratio between BAP and gibberellic acid (GA 3 ) in two nutrient media for shoot elongation. Nodal segments from H12, H19 and H20 clones were disinfected with 0.5, 1.0, 1.5 and 2.0% (v v BAP on ½MS resulted in the longest shoots, for H12 and H20, respectively. Regardless of clone, the rooting rate was low, with an average of 12.0% and 14.4% of plants having roots for in vitro and ex vitro conditions, respectively.Keywords: in vitro establishment, culture medium, cloning, BAP, NAA, GA 3 . RESUMO. Micropropagação de um híbrido de Eucalyptus (Eucalyptus benthamii xEucalyptus dunnii). Objetivou-se micropropagar E. benthamii x E. dunnii, testando concentrações de cloro para a assepsia de explantes, a concentração ótima de benzilaminopurina (BAP) e ácido naftalenoacético (ANA) para a proliferação de gemas e a relação entre BAP e ácido giberélico (GA 3 ) em dois meios de cultura para o alongamento de brotações. Segmentos nodais dos genótipos H12, H19 e H20 foram desinfetados com 0,5; 1,0; 1,5 e 2,0% (v v

Tissue Culture of Corymbia and Eucalyptus

“…Eucalypt shoots sometimes produce roots spontaneously in hormone-free medium or potting mix [45,46,64,88,92,96,104,113,119,143,144,150,161]. However, adventitious rooting on eucalypt shoots is usually induced with an auxin rooting hormone, typically IBA at a concentration between 0.49 and 49 µM (Table A1).…”

“…Sucrose at 87.6 mM has been used in proliferation media for Corymbia species and hybrids even when 58.4 mM sucrose was used in the establishment medium [45,46,64,69,87]. A lowered sucrose level of 43.8 mM has been used during elongation [92] or both proliferation and elongation [93] of E. benthamii × E. dunnii shoots. The sucrose level has been dropped from 58.4 mM in the proliferation phase to 29.2 mM to promote elongation of E. grandis × E. urophylla shoots prior to transfer to root induction media [104].…”

“…However, cytokinins prevent adventitious rooting and so it is unclear why auxin rooting hormones are added to shoot proliferation media that contain cytokinins. Cytokinin levels are often reduced during long-term maintenance of cultures or for a single passage prior to root induction [80,92,93,107,108]. The gibberellins, GA 3 at 0.29-0.58 µM or GA 4 at 0.5 or 1 µM, have been added for a single passage to promote elongation of E. benthamii × E. dunnii and E. impensa Brooker & Hopper shoots, respectively, prior to root induction [70].…”

“…For example, C. torelliana × C. citriodora shoots can be transferred after 3-7 days on IBA-containing medium to tubes containing sterile potting mix, with the tubes placed in sterile 1-L plastic containers that are covered initially with another container to create a humid sealed volume of 2 L [41,45,46,64,120]. Shoots of E. benthamii × E. dunnii, E. grandis × E. camaldulensis, E. grandis × E. tereticornis, and E. grandis × E. urophylla have been transferred directly ex vitro after auxin treatment [92,167]. Shoots of E. benthamii × E. dunnii and E. grandis × E. camaldulensis have also been transferred directly ex vitro without an auxin treatment, as have E. cloeziana and E. dunnii shoots [92,96,99,104,119].…”

“…ex Woolls, and E. urophylla have been germinated on sterile moistened filter paper prior to transfer to semi-solid media for shoot culture or callogenesis [85][86][87]. Anti-browning agents such as polyvinylpyrrolidone (PVP), ascorbate, and activated charcoal are sometimes added to the establishment medium to improve eucalypt explant survival [16,[88][89][90][91][92][93][94][95]. Antibiotics can also be used during establishment to reduce bacterial or fungal contamination.…”