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 (GA3) 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 -1 ) of chlorine. Explants were grown on ½MS medium supplemented with BAP (0, 0.25, 0.50, 0.75 and 1.00 mg L -1 ) and NAA (0, 0.025, 0.050, 0.075 and 0.100 mg L -1 ) for bud production. They were elongated on MS and ½MS media supplemented with BAP (0, 0.05 and 0.10 mg L -1 ) and GA3 (0, 0.1, 0.2 and 0.3 mg L -1 ). The 0.50 mg L -1 BAP and 0.050 mg L -1 NAA combination was optimal for bud proliferation for H12 and H20. GA3 concentrations of 0.10 and 0.20 mg L -1 combined with 0.10 mg L -1 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.
Highlights
Important Eucalyptus species or varieties adapted to severe climate conditions are limited, but E. benthamii and E. dunnii stand out among these species, offering the possibility of climate adaptation and quality wood production
Bennett et al (1994) recorded that BAP concentrations above 2.5 μM (≈ 0.56 mg L-1) on MS medium reduced the average number of buds per explant of E. globulus, which was similar to the results found in the present study, where concentrations over 0.5 mg L-1 BAP reduced the number of buds per explant (Figure 1)
It was verified that the genotype had low rooting rates, even when cultivated in vitro, similar to the rates observed for ex vitro conditions. These results show that E. benthamii x E. dunnii hybrid material can be directly rooted ex vitro, maximizing micropropagation process tested
Summary
Important Eucalyptus species or varieties adapted to severe climate conditions are limited, but E. benthamii and E. dunnii stand out among these species, offering the possibility of climate adaptation and quality wood production. In regions where severe frosts compromise the establishment and growth of Eucalyptus, resistance to cold conditions is a crucial feature that may be introduced by interbreeding (BORÉM, 2007). It was shown that the occurrence of spontaneous hybrid formation between E. benthamii and E. dunnii at Embrapa Forests in Colombo, Paraná State, might present frost-tolerant varieties. E. benthamii and E. dunnii hybrids are an alternative for future forest plantations, due to frost tolerance and low temperature resistance (HIGA et al, 2000; JOVANOVIC et al, 2000). 655-663, 2011 mainly because of the high price and low availability of hybrid seeds. Before the commercial use of these hybrids can be completed, studies are required to identify methods for obtaining seeds or plants from those hybrids
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