Optimization of the micropropagation of elite adult trees of Sequoia sempervirens: forest species of interest in the Basque Country, Spain

Abstract

Forest trees are renewable sources of timber and other valuable non-timber products. Nowadays, the increase in population and demand for forestry products results in overexploitation of forestry. Therefore, there is an urgent need to produce elite plants with higher productivity under stress derived from climate change to have available to afforestation. For this reason, propagation methods should be improved to be more efficient in terms of quality and productivity. The main species planted in the Basque Country is Pinus radiata; during the last three years, Pinus radiata plantations have suffered a fungus attack affecting mainly needles until the tree's death. This crisis is caused by the combined action of two fungi of the genus Dothistroma and Lecanosticta acicola, whose expansion seems to have been enhanced by weather-related factors, such as humid and hot summers. Although we have evidence of this disease's presence in our mountains since 1942, the disease has had a speedy expansion with an aggressive effect for reasons that are not scientifically known today. For the above, Basque Country forestry sector is looking for alternative species to be used in its plantations. Part of the forestry sector considers that Sequoia sempervirens could be a good choice for plantations. Besides, its high-quality wood and its tolerance to the attack of several pathogens and other diseases derived from climate change are characteristics that could confer some advantage over other forest species. The main goal of this study was to optimize the micropropagation of adult elite trees of Sequoia sempervirens. The effect of 6-benzylaminopurine, meta-Topolin and Kinetin, and 4 types of explant in the multiplication stage were analyzed to carry out this objective. Furthermore, the effect of two types of auxins: 1-naphthalene acetic acid, indole-3-butyric acid, and a mixture of both, were evaluated on the induction of roots and their subsequent effect on the acclimatization process. The best multiplication index was obtained when 4.4 µM 6-benzylaminopurine and apical explants longer than 1.5 cm of length were used. The root induction percentage was 75% in the most responsive genotype analyzed when 4.4 µM 6-benzylaminopurine was used on the induction stage, and 50 µM of 1-naphthalene acetic acid was used for rooting. Finally, after 3 months in the greenhouse, the explants cultured with Kinetin and rooted in a culture medium with indole-3-butyric acid showed the highest acclimatization success (94%).

Adult Trees Cryptomeria japonica (Thunb. ex L.f.) D. Don Micropropagation: Factors Involved in the Success of the Process

“…The highest NS/E was obtained in BT explants cultured in QL medium (Experiment 1). In accordance with this result, in previous experiments in our lab, the highest number of NS/E was obtained in S. sempervirens when explants bigger than 1.5 cm in length were used [10]. Similarly, Hine et al [29] and Rafi and Salehi [44] developed an in vitro protocol for C. japonica and Cedrus deodara, using explants of mature trees from 1.0 to 2.5 cm in length, respectively.…”

“…During Experiment 2, explants cultured with BA or m-T showed an efficient organogenic response regarding shoot induction percentage, and although not significant, a slightly higher response in BT explants induced with BA was observed. Analogous results were obtained in several organogenesis protocols from adult trees of Pinus pinea, P. radiata, Sequoia sempervirens, and P. halepensis, where, to obtain an in vitro shoot response, BA at concentrations ranging from 4.4 to 50 µM was utilized [10,[40][41][42][43].…”

“…Micropropagation starting from nodal segments uses smaller explants than conventional techniques, and selection of juvenile explants is possible [8]. With regard to explants coming from mature trees, they are less likely to dedifferentiate and reprogram [9], but the use of explants from mature trees for conifer micropropagation has also been reported [10,11]. However, because these trees are selected after reaching maturity, there has been limited success reported in the vegetative propagation of mature conifers, and procedures should be improved.…”

Testing Explant Sources, Culture Media, and Light Conditions for the Improvement of Organogenesis in Pinus ponderosa (P. Lawson and C. Lawson)

“…In the same way, in P. sylvestris and P. pinaster , a higher rate of organogenic response was obtained by using m-T instead of BA [ 36 , 46 ]. However, in other studies of our group, no improvement was found when using m-T instead of BA for the induction of axillary shoots in P. radiata and Sequoia sempervirens [ 20 , 32 , 41 ]. Summarizing, the effect of different cytokinins at different concentrations depends on the species and the initial explant used to initiate the in vitro culture.…”

“…As has been recently reviewed, factors such as explant source and plant growth regulators influence the in vitro regeneration of plants via organogenesis in different species [ 30 , 31 , 32 ]. In this regard, other authors mentioned that cotyledon explants had several advantages over embryonic explants [ 33 , 34 ].…”