INFLUENCE OF CULTURE MEDIUM, EXPLANT LENGTH AND GENOTYPE ON MICROPROPAGATION OF Pinus taeda L.

This work aimed to establish a micropropagation protocol for Pinus taeda L. Apical shoots from 5-day seedlings, of different genotypes (F27, B05 and PC), were cultured on WV5 medium supplemented with 44 mu M 6-benzylaminopurine (BAP) and 0.05 mu M alpha-naphtaleneacetic acid (NAA), for 14 days, followed by subcultures on growth regulator-free medium. Explants were sectioned into apical shoots and nodal segments for multiplication. Different lengths of explants, BAP concentrations and cultivation periods were tested. Rooting was induced on WV5/2, WV3/2, GDm/2 and agar-water culture media supplemented with 2.68 mu M NAA and 0.44 mu M BAP for nine days, followed by a 4-week subculture on growth regulator-free medium. It was verified that genotype influenced shoot formation and rooting. The length of 1.0 cm is recommended for nodal segment explants to obtain a high number of axillary shoots. For apical shoots, 0.5 cm explant and WV5 medium formulation allowed the best results for elongation. The best period of subculture was eight weeks, both for nodal segments and for apical shoots. The higher percentage of nodal segments with shoots (99.2%) and the higher average number of shoots per explant (4.0) were obtained with F27 genotype in medium culture containing 2.5 mu M BAP. For apical shoots, the best result for elongation was observed for the shorter explants (0.5 cm) on WV5 culture medium (218.3%). The maintenance of in vitro clonal micro garden of vigorous shoots was obtained for two years of 8-week subcultures on WV5 culture medium. The best rooting rate (55.6%) was obtained when shoots were inoculated in agar-water medium with 2.68 mu M NAA and 0.44 mu M BAP for nine days. Plantlets were successfully acclimatized (85% of survival), so a micropropagation protocol was established.