In vitro germination and development of western hemlock dwarf mistletoe

A procedure for in vitro culture of the parasitic flowering plant western h emlock dwarf mistletoe, Arceuthobium tsugense (Rosend.) G.N. Jones subsp. t sugense, is described. A factorial experiment evaluated the effects of medi a (Harvey's medium (HM) and modified White's medium (WM)), temperatures (15 degreesC and 20 degreesC), presence or absence of light, and plant growth regulators (the auxin 2,4-dichlorophenoxyacetic acid (2,4-D) and the cytoki nin 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 degreesC in the presence of light and without plant growth regulators. Som e 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 rad icles, and callus arose from split holdfasts. Factors that promoted holdfas t production were Harvey's medium, light, and 2,4-D at 1 mg l(-1). Callus d evelopment 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 degreesC in the dark.