Abstract
Micropropagation of Pinus taeda by axillary bud proliferation technique and anatomical study of adventitious roots were studied. Apical and basal segments were establishedin vitro in Murashige and Skoog (MS) culture medium. For multiple shoot induction, the explants were transferred to WV3 medium with or without 6-benzylaminopurine (BAP) (0.12, 0.25 or 0.50 µM). The effect of the culture medium and combinations of α-naphthalene acetic acid (NAA) with BAP on adventitious rooting were evaluated. The basal segments exhibited higher multiplication rates (3.7 shoots per explant) than apical segments during establishment of in vitro culture. The best rooting rate (40%) was achieved by induction of roots in water-agar (WA) culture medium supplemented with 2.69 µM NAA and 0.44 µM BAP, for 9 days, followed by transfer into GDm/2 medium. Adventitious roots can be derived from the cambium cells, from adventitious meristem, or from a callus developed at the base of the shoots. When formed indirectly, roots can be derived from peripheral cells of the callus. In treatment resulting in the best rooting rate, 58.3% of the roots were formed directly. The callus formation at stem basis did not prevent rooting and did not impair acclimatization. The plantlets were successfully acclimatized with 90% survival. Key words: Loblolly pine, apical segment, basal segment, rooting, vascular connection, callus.
Highlights
Pinus taeda L. is an important forest species because of the productivity and quality of its timber, being used primarily at sawmills, rolling mills, manufacturing of particle board, MDF, construction, furniture, crates, pulp and paper (Schultz, 1997)
The best rooting rate (40%) was achieved by induction of roots in water-agar (WA) culture medium supplemented with 2.69 μM naphthalene acetic acid (NAA) and 0.44 μM BAP, for 9 days, followed by transfer into Gresshoff and Doy modified culture medium (GDm)/2 medium
Basal segments showed a higher percentage of explants forming axillary shoots (90 to 100%) and average number of shoots per explant (3.7), compared to apical segments (Table 1; Figure 1b and c)
Summary
Pinus taeda L. is an important forest species because of the productivity and quality of its timber, being used primarily at sawmills, rolling mills, manufacturing of particle board, MDF, construction, furniture, crates, pulp and paper (Schultz, 1997). Research on vegetative propagation of Pinus is of great importance and has been applied to improve the quality of its wood and plantation. It is frequently still propagated from seed, since the rooting of cuttings depends on the season of the year or on the availability of juvenile material (Schestibratov et al, 2003; Alcantara et al, 2007; Cuesta et al, 2008; Andrejow and Higa, 2009). The micropropagation techniques became a necessary tool for large-scale production of P. taeda plants and serve as strategies for tree improvement (Gupta and Durzan, 1991; Govil and Gupta, 1997; Menzies and Aimers-Halliday, 1997)
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