Development of a Micropropagation Protocol for the Ex Situ Conservation of Nuttall's Scrub Oak (Quercus dumosa)

Worldwide, oak species are threatened with extinction due to habitat loss, pathogens, and changing fire regimes. Ex situ conservation through tissue culture may protect the remaining genetic diversity of Quercus dumosa, or the coastal sage scrub oak, from further loss. We designed three basal salt formulations based on the mineral composition of shoot tips and first leaves from mature Q. dumosa and explored carbohydrate source, stress-mitigating compounds, and plant growth regulator concentrations to develop a method of cultivating many Q. dumosa culture lines in vitro. All three novel basal salt formulations led to decreased necrosis compared with commercial basal salt formulas WPM, MS, and DKW. Substitution of 30 g L^-1 sucrose with glucose and adding 250 mg L^-1 ascorbic acid, 5.2 mg L^-1 SNP sodium nitroprusside, and 103 mg L^-1 y-aminobutyric acid improved culture health overall. In an experiment involving 115 culture lines, 0.66 mg L^-1 6-benzylaminopurine produced the highest average shoots per explant, but 0.33 mg L^-1 produced the greatest proportion of shoots 2 cm or greater. Incubation for 24 h in 20 mg L^-1 indole-3-butyric acid led to the most rooting. These methods show promise for the ex situ conservation of many genotypes of endangered Q. dumosa.