In vitro germination and development of western hemlock dwarf mistletoe

A procedure for in vitro culture of the parasitic flowering plant western hemlock dwarf mistletoe, Arceuthobium tsugense (Rosend.) G.N. Jones subsp. tsugense, is described. A factorial experiment evaluated the effects of media (Harvey's medium (HM) and modified White's medium (WM)), temperatures (15 °C and 20 °C), presence or absence of light, and plant growth regulators (the auxin 2,4-dichlorophenoxyacetic acid (2,4-D) and the cytokinin 6-benzylaminopurine (BAP) at varying concentrations (0.001 mg l⁻¹ to 1 mg l⁻¹)). Seed explants germinated in less than one week in culture and produced radicles. Optimal conditions for radicle elongation were WM at 20 °C in the presence of light and without plant growth regulators. Some of the radicles split at the tip to yield callus while others swelled to become spherical holdfasts. Holdfasts were also produced at the tips of radicles, and callus arose from split holdfasts. Factors that promoted holdfast production were Harvey's medium, light, and 2,4-D at 1 mg l⁻¹. Callus development from split radicles and split holdfasts was optimal on WM with 0.5 mg l⁻¹ 2,4-D and 1 mg l⁻¹ BAP at 20 °C in the dark. This revised version was published online in June 2006 with corrections to the Cover Date.