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Plant Focus

Quercus peninsularis
A Red Oak (Section Lobatae) endemic to inland ranges of northern Baja California, Mexico

Shoot-Tip Cryopreservation for Oak Conservation

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Gillian M. Ross and Valerie C. Pence

Published May 2023 in International Oaks No. 34: 149–158


Because conventional seed banking is not an option for oaks, ex-situ conservation requires living collections and/or tissue cryopreservation. Demonstrated cryopreservation options for oaks include zygotic embryos, somatic embryos, and shoot-tips, but the development of these as conservation tools is in its infancy. The objectives of the Oak Cryopreservation Project at the Center for Conservation and Research of Endangered Wildlife (CREW) are to 1) initiate a variety of species into in-vitro culture, 2) evaluate shoot-tip survival through cryopreservation, and 3) compare shoot-tip and somatic embryo cryopreservation.  To date shoot-propagating cultures of nine species have been initiated, including two threatened species (Quercus hinckleyi and Q. arkansana); four species are in early establishment (including Q. acerifolia), and others are newly cultured (including Q. georgiana). Differences in species’ responses have been observed both in survival through cryopreservation and growth in vitro. For example, the use of the ethylene inhibitor silver thiosulfate (STS) in the growth medium can alter the phenotype of some species but not others. Factors including STS, light intensity, antioxidants, growth temperature, and cryoprotectants have been examined for their effects on cryosurvival. Cold hardening of cultures and post-cryo recovery growth with cooler night temperatures have improved survival through cryopreservation and recovery with some species, particularly Q. virginiana. Other factors examined thus far have not shown a positive effect. Cryopreservation has a demonstrated potential for conservation of oaks, but further work is required to broaden its applicability to all oak taxa.


cold hardening, exceptional plant, Quercus


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