In vitro propagation and reintroduction of golden paintbrush (Castilleja levisecta), a critically imperilled plant species

Abstract

Golden paintbrush (Castilleja levisecta Greenm.) is a hemiparasitic herbaceous perennial native to the Pacific Northwest of North America and is considered critically imperilled with only 11 populations remaining in the wild. The main objective of this study was to develop ex situ and in situ conservation through micropropagation and field plantings. In vitro cultures were initiated using nodal explants from two plants raised from seeds collected from a natural population. Shoots were then multiplied on Murashige and Skoog basal medium with 2.0 μmol L−1 6-benzylaminopurine (BA), 3.0 μmol L−1 kinetin (Kn), 2.2 g L−1 phytagel, and 3% sucrose. Explant position on source plants, culture vessel design, and application of different plant growth regulator levels for BA, Kn, and thiadiazuron (TDZ) were tested to optimize micropropagation protocols. Clones from the plants showed differences in plant height and number of nodes in response to various BA and TDZ concentrations. In vitro shoots were successfully rooted under ex vitro conditions using commercial rooting powder (0.8% indole-3-butyric acid) with an average of ∼17 roots per shoot and acclimatized in the greenhouse with 100% survival rate. Two-month-old plants were transferred to a Parks Canada restoration site at Fort Rodd Hill, Victoria, BC, with 7.5% survival. The use of micropropagation in combination with reintroduction efforts offers an excellent opportunity for conserving endangered plant biodiversity in vitro and facilitating in situ conservation efforts by providing plants for reintroduction.