Submitted to: CryoLetters
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: May 1, 2013
Publication Date: October 31, 2013
Citation: Jenderek, M.M., Holman, G.E., De Noma, J.S., Reed, B.M. 2013. Medium- and long-term storage of the Pycnanthemum (Mountain mint) germplasm collection. CryoLetters. 34:490-496. Interpretive Summary: Mountain mint germplasm that does not produce seeds is maintained clonally in pots and backed-up in test tubes. Plants maintained in the tubes have to be often subcultured to keep alive. To avoid the resource consuming subculturing, a method for a medium- and long-term storage was developed. For a medium-term (>2 years) storage, the Mountain mint germplasm was kept at 4oC in special plastic bags on a medium without growth regulators. For a long-term, the plants were cryopreserved (-196oC) using an encapsulation-dehydration technique. The survival of the cryopreserved material was between 40 and 100%. The results of the study contributed to the development of conservation methods for clonally propagated Mountain mint.
Technical Abstract: The US collection of mountain mint (Pycnanthemum Michx.) is held at the USDA-ARS National Clonal Germplasm Repository (NCGR) in Corvallis, OR as seed, potted plants and tissue cultures and a long-term storage collection is preserved at the USDA-ARS National Center for Genetic Resources Preservation (NCGRP) in Fort Collins, CO. The clonal collection is comprised of 34 accessions as potted plants that are duplicated with 31 accessions stored as in vitro cultures at 4°C in tissue culture bags for medium-term storage at NCGR and as cryopreserved shoot tips in liquid nitrogen at NCGRP for long-term storage. This study reports on these two models of preservation of Mountain mint at the U.S. National Plant Germplasm System. In vitro plants required 2 to 7 months for propagation on MS medium without growth regulators before storage at 4°C. Plants remained in storage with good vigor in bags on ½x nitrogen MS medium without growth regulators for a mean of 2.08 yr. An encapsulation-dehydration protocol was successful for cryopreservation of shoot tips from cold acclimated in vitro plants. Post cryo viability, indicated by shoot tips with developed leaves and roots, ranged from 60 to 100% for 27 accessions and 40 to 50% for the other four. The encapsulation-dehydration cryopreservation method proved suitable for long-term preservation of the 31 Pycnanthemum accessions. These alternative storage forms allow for active use of the collection as well as base storage for clonally propagated accessions.