Effect of different cytokinin sources on in vitro/ex vitro multiplication and rooting rate in Eucalyptus spp.

Abstract

Eucalyptus globulus Labill. is of great interest to the pulp industry. However, the species is highly susceptible to leaf spot caused by Teratosphaeria nubilosa and has a low rooting capacity. In order to overcome these limitations, INIA has been implementing a genetic improvement program for this species and the generation of interspecific hybrids. The strategy is based on the selection of E. globulus clones with high precocity or foliage turnover, since the adult foliage is more tolerant to T. nubilosa. In addition, controlled crosses of E. globulus and E. maidenii with E. grandis are carried out to incorporate disease resistance and ease of rooting. The multiplication of the selected materials is carried out by micropropagation, but the low rooting capacity is a trait that needs improvement. The cytokines necessary for in vitro proliferation can have a negative effect on the rooting process. Benzyladenine is the most commonly used cytokine because of its low cost and easy availability, with some negative effects on rooting, while meta-topolin is a cytokine of lesser impact. The objective of this study was to evaluate the effect of benzyladenine and meta-topolin on the multiplication rate, rooting percentage and plantlets survival of E. globulus, E. grandis × E. globulus, and E. grandis × E. maidenii. In multiplication media, benzyladenine was supplied at 0.4 µM, while two concentrations of meta-topolin (0.4 and 2 µM) were used. Preliminary results indicated a higher multiplication rate with the inclusion of meta-topolin in both concentrations. The in vitro rooting percentage of explants treated with meta-topolin was 51% and 44%, at 0.4 and 2 µM, respectively, while with benzyladenine was lesser (37%). After 28 days post-transplanting, survival was higher in meta-topolin-derived plants. Meta-topolin improved multiplication, in vitro rooting and acclimation of plants. The use of this hormone could improve micropropagation protocols, facilitating rooting and multiplication of valuable genotypes.