Protocols for Micropropagation of Woody Trees and Fruits

CHAPTER 11
MICROPROPAGATION OF YEW (TAXUS BACCATA L.)
D. EWALD
Federal Research Centre for Forestry and Forest Products, Institute for Forest
Genetics and Forest Tree Breeding, Eberswalder Chaussee 3A, D-15377
Waldsieversdorf, Germany
1. INTRODUCTION
Yews are slow-growing shade tolerant trees which were used over millennia because
of their durable and elastic wood, especially for weapons like longbows. This led to
an extreme shortage of this material and a dramatic negative selection for phenotypes
with straight stem forms over four hundred years ago. After the introduction of fire-
arms, this tree species recovered again. Later on, the accidental poisoning of valuable
domestic animals such as horses caused a further clearing of trees (e.g. near roads).
A growing interest in yew arose again with investigations on the toxic principle 50
years ago. The mitotic spindle poison paclitaxel was an effective inhibitor of fast
growing cancer cells and was mainly concentrated in the bark of the trees. Approximately
seven tonnes of yew bark is necessary to obtain one kilogram of paclitaxel.
Based on this and on similar calculations it became obvious that the supply of plant
material of yew might be limiting factor in the future (Croom, 1995). Therefore,
methods for vegetative cutting propagation were developed and improved in different
countries (Schneck, 1996; Ewald et al., 2002). Micropropagation methods to multiply
selected material were developed at the same time, however, the number of published
results concerning adult plant material is limited (Taxus mairei – Chee, 1995; Chang
et al., 1998, 2001; Taxus baccata – Majada et al., 2000). Somatic embryogenesis of
Taxus, mostly from very juvenile explants such as immature zygotic embryos, was also
reported (Wann & Goldner, 1994) but the regeneration of plants was often difficult
with regard to embryo formation and synchronous development (Taxus brevifolia –
Ewald et al., 1995 and Taxus chinensis – Qiu et al., 1998). Also, somatic embryogenesis
was not satisfactory concerning the percentage of germinating explants
(Taxus brevifolia – Chee, 1996). Testing these previously described in vitro methods
based on organogenesis, often led to failure in the laboratory of the author while
investigating micropropagation of adult yew material. Insufficient tissue culture
117
S.M. Jain and H. Häggman (eds.), Protocols for Micropropagation of Woody Trees and Fruits, 117–123.
© 2007 Springer.