Establishing tissue culture lines from mature Nuttall’s scrub oak (Quercus dumosa Nutt.) for ex situ conservation

Authors: REE, JOSEPH - San Diego Zoo; POWELL, CHRISTY - San Diego Zoo; FOLGADO, RAQUEL - Huntington Library, Art Collections, And Botanical Gardens; PENCE, VALERIE - Cincinnati Zoo & Botanical Garden; Walters, Christina; MASCHINSKI, JOYCE - Center For Plant Conservation (CPC)

Submitted to: In Vitro Cellular and Developmental Biology. Plants
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/26/2024
Publication Date: 1/14/2025
Citation: Ree, J.F., Powell, C., Folgado, R., Pence, V.C., Walters, C.T., Maschinski, J. 2025. Establishing tissue culture lines from mature Nuttall’s scrub oak (Quercus dumosa Nutt.) for ex situ conservation. In Vitro Cellular and Developmental Biology. Plants. 61:102-116. https://doi.org/10.1007/s11627-024-10475-4.
DOI: https://doi.org/10.1007/s11627-024-10475-4

Interpretive Summary: Establishing vegetative cultures of explants collected from woody plants growing outside is challenging. Yet, this process may be necessary to capture genetic diversity of a stand that is suffering from reproductive failure (i.e., no seed set). In this work, we studied the process using the endangered oak species, Quercus dumosa, Nuttall’s Scrub Oak. Using standard protocols that prevented fresh cuttings from drying out and used medium with commercially available basal salts, explants became 100% necrotic within a few days. By incremental improvements of processing and medium additives, we were able to generate 11 culture lines from 17 source plants. Key improvements occurred when we used antioxidants, plant growth regulator 6-benzylaminopurine, and silver thiosulfate (an inhibitor of ethylene production). This optimized medium provides a good starting point to introduce other plants from coastal sage scrub and chaparral ecosystems into culture.

Technical Abstract: Quercus dumosa, a scrub oak native to the coastal sage scrub and chaparral ecosystem of Southern California and Baja California, is endangered, and its remaining populations face many threats. Because technologies do not currently exist to bank Q. dumosa acorns, the species requires alternative strategies for ex situ conservation, such as tissue culture. During initial trials, nodal segment explants created from fresh growth harvested from native populations of mature trees showed necrosis within several days when placed on WPM medium with 30 g L-1 sucrose, 1 mg L-1 BAP, and 8 g L-1 agar. Explant survival increased steadily through protocol optimization experiments, and, eventually, we could reliably establish and grow stable culture lines derived from mature Q. dumosa trees. After disinfestation, explants were dried on autoclaved filter paper to remove excess water, sectioned into nodal segments, and then placed on a medium composed of basal salts designed for Q. dumosa, 45 g L-1 glucose, 250 mg L-1 ascorbic acid, 50 mg L-1 phloroglucinol, 100 mg L-1 polyvinylpyrrolidone, 100 mg L-1 glutathione, 0.33 mg L-1 6-benzylaminopurine, and 20 µM silver thiosulfate. This medium led to the creation of stable culture lines from 11 of 17 source plants, suggesting that it can be used for the ex situ conservation of Q. dumosa. Additionally, 27 of 34 other species native to the coastal sage scrub ecosystem established at least one culture line on this medium, suggesting that this protocol has utility beyond Q. dumosa.