AN N ALS OF SILV IC U LTU RAL RESEARCH 44 (1), 2020: 41-46 https://journals-crea.4science.it/index.php/asr Technical note Special Issue: HORIZON 2020 GA 728086 WOODnat “Second generation of planted hardwood forests in the EU” http://dx.doi.org/10.12899/asr-1929 1 Bosques Naturales SA, Alcobendas, Madrid – Spain *Corresponding author: jesusfernandez@bosquesnaturales.com Introduction Walnut trees are species of the genus Juglans spp. L., traditionally characterized by their high- ly-valued nuts and timber. Considering the high timber value and the shortage of the species, many walnut forest plantations oriented for tim- ber production have been established during the last decades (Mohni et al. 2009). These plantations have been established with the common species of Persian or European walnut (J. regia L.) and Black or American walnut (J. nigra L., J. major (Torr.) A. Heller, J. hindsii (Jeps.) Jeps. ex R.E. Sm.) but also with several hybrids which have been specificall developed for timber production, e.g.: Mj-209xRa y Ng-23xRa (Aletà 2004, Victory et al. 2006, Mohni et al. 2009, Clark and Hemery 2010, Coello et al. 2013). The success of this kind of planted forests have been very variable and the genetic material is con- sidered as one of the main drivers (together with site selection and forest management) for the success or failure of the plantations (e.g. Aletà et al. 2003, Aletà 2004, Urbán-Martínez et al. 2013, Licea-More- no 2016). To this respect, Aletà and Vilanova (2006) pointed out the high variability in the performance of the trees from seed material, despite the trees are genetically close between them. Considering the relevance of this genetic material selection for wal- nut (Juglans spp.) planted forests oriented for tim- ber production, there have been two big research groups working in the clone selection in Spain: 1) from the public center IRTA (e.g. Aletà et al. 2003, Aletà 2004) and 2) from the private company Bos- ques Naturales SA (e.g. Urbán-Martínez et al. 2013, Licea-Moreno 2016). To this respect, the Spanish Register for Forest Reproductive Material includes 29 clones (21 for J. nigra, 8 for J. regia and 10 for J. x intermedia), 9 parents of family (5 for J. regia and 4 for J. x intermedia) and one seed orchard of J. regia (MAPA 2016). Urbán-Martínez et al. (2013) published a de- tailed characterization of the selection process of the Bosques Naturales SA clones. At the moment, the in-vitro micropropagation plant production is focused in 4 clones (D-15, D-117, D-53 and D-M) selected by their vigour, trunk straightness (based on the classification of MacDonald et al. [2001)) and wood quality. The clone D-15 (commercial name NAT-7-BN] is the one most widely used by the company because it was one of the firsts to be in- troduced in vitro. The original D-15 plus tree is in Cáceres and it had, with 12 years old, 13.5 m height, Clonal effect on rooting and acclimation rates for in-vitro micropro- pagation in hybrid walnut (Juglans x intermedia Mj 209): preliminary observations Jesus Fernández-Moya 1* , Ricardo Julian Licea-Moreno 1 , Ignacio Urbán-Martínez 1 , Ruth M. Castro-Fernández 1 , Cristina Ramírez-López-Ramallal 1 Received 3/09/2019 - Accepted 4/01/2020 - Published online 07/02/2020 Abstract - The success of walnut (Juglans sp.) planted forests for timber production have been very variable and genetic material is considered as one of the main drivers (together with site selection and forest management) for the success or failure of the planta- tions, as the performance of the trees from seed material is very variable. Considering the relevance of this genetic material, several clones have been selected and research have been conducted in order to improve micropropagation procedures. The objective of the present study is to analyze the effects of different clones in the rooting and acclimation rates for in-vitro micropropagation in hy- brid walnut (Juglans x intermedia Mj 209). The results show a signifcative effect of clones on the rooting and the total micropropagation effciency rates, but not on the acclimation rate. The effciency rate of D-117 (65%) is considered statistically higher than the one for D-15 (38%), caused by a higher rooting rate of D-117 (73%) compared with D-15 (55%), because acclimation rate (57%) did not show any clone effect. Considering these differences in the micropropagation success, it might be considered (together with other factors) for clone selection to increase the general performance of the plant production units in large-scale propagation. Keywords - clone selection, hybrid walnut, microprogation, vitroplants, rooting, acclimation.