Introduction

The increasing global need for food and fiber results in new demands for the efficiency of wood production and wood products (Fenning and Gershenzon

2002) which has to be attained on the basis of sustainable development. The majority of world wood products still comes from natural and semi-natural forests, but there is a clear trend towards more efficient plantation forestry (Walter 2004). Development of vegetative propagation methods, including cutting technology, organogenesis and, in particular, somatic embryogenesis will yield additional profit for plantation forestry by the exploitation of non-additive genetic variation, by providing more homogenous material and by compensating potential shortage of improved seed stock. However, economically relevant clonal plantation forestry is currently a reality for only a few species, out of which Pseudotsuga menziesii Mirbel Franco, Pinus taeda L., Pinus radiata D.Don, Populus spp., Eucalyptus spp. and Picea spp. are prominent (Sutton 1999a,b; Peña and Séguin 2001; Cyr and Klimaszewska 2002).

Conventional breeding of forest trees is in many cases hindered by long generation times and self-incompatibility mechanisms. Genetic transformation of forest trees has been considered the mechanism to achieve genetic gain when combined with conventional breeding and plantation forestry. There are several traits that show potential for a molecular breeding approach, e.g. reduction of generation time, production of sterile trees, pest or disease resistance, wood formation (including lignin and cellulose engineering), resistance to biodegradable herbicides, durability, phytoremedia-tion of polluted sites and the production of novel chemicals and pharmaceuticals (reviewed by Peña and Séguin 2001; Fenning and Gershenzon 2002; Diouf

2003). Highly complex traits such as wood formation and the shortening of the juvenile phase have been considered the most important ones for achieving gain and for further domestication (Fenning and Gershenzon 2002).

1 University of Oulu, Department of Biology, Oulu, Finland

2 University of Helsinki, Department of Applied Biology, Helsinki, Finland

3 Finnish Forest Research Institute, Punkaharju Research Unit, Punkaharju, Finland

4 Department of Forestry and Environmental Resources, North Carolina State University, Raleigh, NC, USA

5 Finnish Forest Research Institute, Suonenjoki Research Unit, Suonenjoki, Finland

M.Fladung and D.Ewald (Eds.)

Tree Transgenesis: Recent Developments

© Springer-Verlag Berlin Heidelberg 2006

Future challenges will most certainly include an improved understanding of wood formation as well as the characterising the controlling genes with particular respect to their expression and regulation (Hertzberg et al. 2001; Lorenz and Dean 2002; Raes et al. 2003). Lignin biosynthesis is now quite well understood and modifications with regards to lignin content and quality have progressed well (reviewed by Boerjan et al. 2003). This provides an option for some practical applications in a commercial plantation forestry environment.

Together with the technological aspects of lignin modified trees, the potential environmental impacts of lignin modification have to be considered carefully. The environmental concerns on lignin modified trees have originated from views on the specific characteristics of forest trees. Trees are long-living organisms, many of which are wind pollinated. As primary producers they make contributions to community structure and ecosystem processes, such as nutrient and carbon cycles. The recognition of potential risks or benefits associated with the operational use and deployment requires comprehensive analyses in both contained use and field trials. Elegant reviews of perspectives on risk in transgenic forest plantations have recently been published by Burdon and Walter (2001), van Frankenhuyzen and Beardmore (2004) and Walter (2004). So far, there is relatively little information on environmental effects of lignin modified trees (Pilate et al. 2002). In this review we will discuss the information available on the environmental aspects of lignin modified trees with a specific focus on lignin modification in the pulp and paper industry as well as on the ecological interactions with insect herbivores and symbiotic ectomycorrhizal fungi.

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