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Title: Cryopreservation of Populus trichocarpa and Salix using dormant buds with recovery by grafting or direct rooting

item Bonnart, Remi
item Waddell, John
item HAIBY, KATHY - Greenwood Resources, Inc
item WIDRLECHNER, MARK - Iowa State University
item Volk, Gayle

Submitted to: CryoLetters
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/4/2014
Publication Date: 12/16/2014
Citation: Bonnart, R.M., Waddell, J.W., Haiby, K., Widrlechner, M., Volk, G.M. 2014. Cryopreservation of Populus trichocarpa and Salix using dormant buds with recovery by grafting or direct rooting. CryoLetters. 35(6):507-515.

Interpretive Summary: Black cottonwood (Populus trichocarpa) and willow (Salix) species are valued for their timber, plywood, pulp, paper, ornamental and revegetation uses. P. trichocarpa has also been a model tree genetic system due to its small genome size, rapid growth rate, and short time to maturity. Collections of diverse breeding materials, as well as genomic and genetic resources, are expensive to maintain in field, greenhouse, or in vitro conditions. We used dormant buds of P. trichocarpa and Salix as source materials for cryopreservation experiments to determine the feasibility of backing up field collections with cryopreserved germplasm. Viability assessments were performed by either grafting or by direct rooting and shoot elongation. High levels of regrowth after exposure to liquid nitrogen vapor, as measured by grafting, were observed for all 12 accessions of P. trichocarpa that were studied. Ten of 11 diverse accessions of Salix were recovered by rooted cuttings after exposure to liquid nitrogen vapor. This work demonstrated that dormant bud methods could be successfully implemented for long-term back up of some field collections of Populus trichocarpa and Salix.

Technical Abstract: Populus trichocarpa and Salix can be successfully cryopreserved by using dormant scions as the source explants. These scions (either at their original moisture content of 48 to 60% or dried to 30%) were slowly cooled to –35 degree Celsius, transferred to the vapor phase of liquid nitrogen (LNV,-160 degree Celsius), and warmed before determining survival. Dormant buds that were harvested from P. trichocarpa clones from Puget Sound, WA and Boardman, OR had regrowth levels between 42 and 100%. Direct rooting of thawed P. trichocarpa was also possible. Ten of 11 cryopreserved Salix accessions, representing 10 different species, exhibited at least 40% bud growth and rooting after 6 weeks when a bottom-heated rooting system was implemented. These results demonstrate that dormant buds of P. trichocarpa and Salix accessions can be cryopreserved and successfully regenerated without the use of tissue culture.