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Title: Salix dormant buds cryotolerance varies by taxon, harvest year and stem-segment length [\ARS115 Salix ms FY19]

item Jenderek, Maria
item Ambrusz, Barbara
item Holman, Gregory
item Carstens, Jeffrey
item ELLIS, DAVID - International Potato Center
item WIDRLECHNER, MARK - Iowa State University

Submitted to: Crop Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/11/2019
Publication Date: 3/5/2020
Citation: Jenderek, M.M., Ambruzs, B.D., Holman, G.E., Carstens, J.D., Ellis, D., Widrlechner, M. 2020. Salix dormant buds cryotolerance varies by taxon, harvest year and stem-segment length. Crop Science.

Interpretive Summary: Preservation of willow genetic resources might be done as field plantings, shoot tips derived from tissue culture, or dormant winter buds stored in liquid nitrogen vapor (LNV; -180 to -196oC) that is described as cryopreservation. The last method is the most cost effective of the mentioned preservation methods. With an emerging trend of using willow species as an energy crop to produce biofuel and the proposed mass cultivation as a short-rotation coppice, willow shrubs and trees are progressively more endangered by blue willow beetle and rust in field plantings and make 'off-site conservation' a high-priority. Research done by USDA-ARS and Iowa State University scientists has established some factors that influence viability of dormant winter buds exposed to LNV. The factors are stem-segment length with the dormant buds, harvest year, taxon and bud viability before processing. Dormant bud appearance before cryo-storage is a good indication of their possible cryotolerance; buds in deep dormancy without any signs of growth have the best chance to survive the ultra-low temperature.

Technical Abstract: Salix L. is one of the few genera that may be cryopreserved as dormant winter buds (DB). The use of DB as source plant material for cryopreservation is more cost effective than are methods that employ tissue culture techniques. Processing DB does not require aseptic conditions or time-intensive cryopreservation procedures. The objective of our study was to evaluate selected factors that affect cryotolerance of eight Salix germplasm accessions representing five species in the USDA-ARS National Plant Germplasm System (NPGS). One-year old branches harvested in January during 2007-2009, were cut into either 6 or 10 cm segments containing at least two DB. Segments were treated with a slow- cooling procedure and stored in a vapor phase of liquid nitrogen (LNV) for at least six days. Control segments were stored at -5oC until planting. The LNV-exposed and the -5oC-stored nodal segments were warmed and direct planted in a cold greenhouse. Six weeks later, the material was evaluated for shoot and root development. Twig segments that developed a shoot(s) were considered viable. Average viability varied among years (0 to 35.1%), species (2.8 to 51.4%), accessions of S. purpurea (8.3 to 30.6%) and the length of the branch segment. Dormant buds on 10 cm segments had a higher viability (82.2 %) than did DB on 6 cm segments (43.9 %), suggesting higher suitability for cryopreservation. In the material studied, Salix DB viability was correlated with branch diameter, the DB density and the ability to develop shoots and roots prior to cryopreservation. The visual appearance of DB before cryoprocessing was an indicator of possible cryotolerance. Interactions among harvest year, species and treatment were evident. These results contributed to the development of and applied Salix DB cryopreservation procedure and suggest that post-cryopreservation viability for the same accession varies between years.