Forest biotechnology has witnessed many new inventions and techniques over the past decade, and it is likely this will continue at an even more rapid pace in the future. As such, it may be difficult to know what to expect from biotechnology, nevertheless, it is important we continue to evaluate the basic forest genetic management principles that should be considered, irrespective of the options that technologies will offer forest managers.
While the biotechnology debate in agriculture will continue to be very instructive to forestry, several issues in forestry are different and will require special attention. This article will briefly 1) summarise biotechnology currently used and being developed in forestry, and 2) explore some of the issues and controversies related to their use.
Biotechnology can be described as "any technological application that uses biological systems, living organisms, or derivatives thereof, to make or modify products or processes for specific use" (CBD, 2000). This can encompass a wide variety of techniques, but the three main areas in forestry that will likely be important are: 1) the use of vegetative propagation methods, 2) the use of molecular genetic markers, and 3) the production of genetically modified trees (GM trees).
Vegetative propagation comprises a broad range of techniques involving manipulation of plant tissue (e.g. sections of stems, leaves, roots, seeds or even cell cultures) which ultimately allows for complete vegetative "re-propagation" of the whole plant, i.e., the production of clonal "varieties" or lines.
The simplest forms of vegetative propagation are the various techniques of grafting and the rooting of stem sections or "cuttings." Some species can root or graft easily onto rootstock, whereas other species may require more elaborate "treatments" in order to be successfully rooted or propagated. In forestry, most commercial scale cloning methods rely on rooted cuttings for reforestation purposes, however, advanced cloning techniques (see below) are also a basic prerequisite for the production of genetically modified (GM) trees. Specific "biotechnologies" related to vegetative propagation in forestry fall into the three main categories of micropropagation, cryopreservation and in vitro storage, and in vitro selection.
Micropropagation. Micropropagation is the development of clonal lines from small tissue samples such as buds, roots or embryos extracted from seeds. The last, referred to as somatic embyrogenesis (SE), will likely be the most promising micropropagation technology for long-term storage and large-scale production of trees from selected clonal lines, particularly for conifer species. SE can be particularly useful once the genetic value of the clones has been determined through field testing. However, the development costs of such advanced tissue culture technologies are high compared with simpler techniques.
Cyropreservation and in vitro storage. With this technique small tissue samples are maintained at very cold temperatures to maintain their current physiological condition. Therefore, the evaluation of genotypes for efficient production of plant material later on is usually one of the main goals of cyropreservation (e.g., in SE storage). While the technology is useful and necessary for many applications in clonal forestry, it may also have applications in programmes for species with recalcitrant seed, where basic seed storage is a major problem (Englemann, 1997).
In vitro selection. This technique involves selecting for a trait (e.g. heavy metal or salt tolerance) at an early stage in the micropropagation phase. Although in vitro selection has been used to some degree in crop plants, attempts in forest trees have been limited to selection of expressed GM traits in trees (i.e., in vitro selection techniques are a basic requirement in the process of screening for successfully GM transformed clonal lines). Other traits, therefore, can be combined with basic in vitro selection criteria required for GM screening (e.g. mercury tolerance in yellow poplar [Rugh et al., 1998]), which could be used for identifying clonal lines useful for phyto-remediation purposes (Guller et al. 2001).
Genetic markers are essentially DNA sequences that are indicative of common ancestry. The challenge to the geneticist is to look for relationships between these markers and characteristics of trees from pedigrees or specific populations. With correct interpretations, genetic markers are invaluable for examining patterns of genetic variation among and within populations, assessing levels of outcrossing and inbreeding, and genetic identification or "fingerprinting" of varieties or pedigrees.
Genetic marker data can also be used for assisting with early selection of better genotypes, rather than waiting for the tree to express the trait much later. However, marker-assisted selection (MAS) is yet being routinely applied in tree breeding programmes, largely because of economic constraints (i.e., the additional genetic gains are generally not large enough to offset the costs of applying the technology). Thus it is likely that MAS will only be applied for a handful of species and situations, e.g. a few of the major commercially used pine (e.g. Frewen et al., 2000) and Eucalyptus species. Molecular markers are therefore primarily an information tool and are used to locate DNA/genes that can be of interest for genetic transformation, or information on population structure, mating systems and pedigree confirmation.
Genetic modification of plants usually involves the artificial introduction of well-characterized genes from other species into a new plant genome, which then expresses itself as a new novel trait. "Biolistics" (i.e. blasting DNA into the cell nucleus) or microorganism vectors (e.g. Agrobacterium) that carry the specific gene of interest are typically used to introduce the gene(s). Of course, long-term or adequate expression of the gene in the GM plant is critical.
To be of economic value, GM trees must offer unique features that cannot be economically delivered through conventional breeding programmes, and that are capable of offsetting the costs in developing the technology. The traits that have so far been considered for potential genetic modification of forest trees are herbicide resistance, reduced flowering or sterility, insect resistance and wood chemistry. While conventional tree breeding programmes have been able to make changes to insect resistance and wood quality, they have limited possibilities of incorporating traits such as herbicide resistance, specific changes in wood chemistry or reduced flowering. With GM technologies, these possibilities are likely to come within reach.
Most of the concern about genetically modified plants, derives from concern about these products grown as food. Although this will rarely be a direct issue in forestry, careful evaluation will still be necessary to all aspects of use of the trees because they can have many purposes.
It is difficult to say that any particular technique in itself can pose increased biological risk. It is the gene products that pose a risk, irrespective of the technology used to obtain them. To evaluate possible risks fully, in-depth knowledge of the particular genetic transformation is necessary, e.g., what is the protein products produced by the transformation in the plant and their possible interactions with other genes. This may be particularly true when more than one or two transgenes are incorporated. In such cases there may be requirements for longer field testing, more environmental assessments and caution in deployment (Burdon, 1999). These issues, however, should not be considered unique to GM trees per se, as they are considerations that tree breeders must consider even for conventionally bred trees.
Herbicide resistance. Herbicide resistance in poplars is probably the most well developed GM technology in forest trees. The first concern with herbicide-resistant GM plants is the evidence of the development of resistance in the weeds. The risk may be substantially less in forestry than in agriculture, as herbicides are only applied for a short period of time, with fewer applications as total weed control is not necessary in forest tree plantations. The introduction of herbicide resistance with GM technology may be one of the most feasible and applied genetic modifications in trees; however, it is only likely for a few well-developed species in certain situations, such as in intensive poplar fibre farms.
The second question is of course related to the effects on adjacent or local wild populations of trees, if cross-breeding does occur (e.g. in important in situ conservation areas). If the acceptability of this risk is too great, reduced flowering or sterility transgenes (see below) may need to be incorporated into GM tree lines.
Reduced flowering or sterility. Reduced flowering in forest trees may be desirable to re-direct products of photosynthesis into wood production, rather than into reproductive tissues. However, since our knowledge of the reallocation of such internal resources in a tree is not well quantified at this point, the main justification for reduced flowering or sterility development is to substantially reduce gene flow to wild adjacent populations of the same species. Although substantial research on flowering mechanisms is under way (e.g., Strauss and Bradshaw, 2001), the stability of sterility-gene expression over time will have to be confirmed in field trials that reflect expected rotation lengths.
Insect resistance. The development of GM insect resistant is now common, but it also creates some of the most complex ecological questions. First, is the possible toxicity of the compounds produced in GM insect-resistant plants when they are grown specifically for human consumption, or in forestry, on non-target animals. Second, there are ecological concerns of cross-breeding with wild relatives as well as the evolution of resistance in the pest populations. Moreover, the long generation time of most tree species allows for many generations of insect populations to challenge a new single-gene resistance mechanism.
The most developed GM approach for insect resistance in both forestry and agriculture, has been the use of genes from a natural insect pathogen, Bacillus thuringiensis (Bt). Poplars are again among the tree species in which the technology is most advanced (e.g. TGERC, 1999; Yifan and Jainjun, 2001). Research and development of other compounds is under way to reduce the reliance on the relatively narrow group of natural Bt toxins (ffrench-Constant and Bowen, 1999). Because of the complex ecological ramifications and public concerns surrounding GM insect-resistant plants, high levels of scientifically sound laboratory and field testing will be required.
Wood property chemistry. Genes important in the pathway of lignin development in wood have been modified to produce unique wood composition in very young trees (e.g. Lapierre et al. 1999: Akim et al. 2001), with the goal of easier and more environmentally friendly pulping. Two important questions that remain in developing lignin-modified varieties or clones are, "how much extra value would there be in plantations using such trees" and "would altered wood show susceptibilities to environmental stresses?" Once again, substantial periods of field testing will be required to answer such questions.
The primary ecological concern with GM plants appears to be from potential problems arising from gene exchange with wild populations. However, in many situations for which GM trees will be considered, it will be with exotic plantation species so this would not be a factor. If not, reduced flowering or sterility is likely to be a basic requirement, as well as implementing more restrictions in deployment. Some investigations to look at these specific questions are under way in forestry (e.g. DiFazio, et al., 1999).
Current regulations of the Forest Stewardship Council (1999) prohibit the use of genetically modified trees, but they also state that "the use of an exotic species shall be carefully controlled and actively monitored to avoid adverse ecological impacts." However, the idea that GM trees might be functionally analogous to some invasive exotic species does not seem very likely (Strauss and Bradshaw, 2001). On the other hand, a large genetic change made to the overall fitness of a native species, even by a single gene addition, and released without adequate consideration of local environmental risks is not appropriate either. Clearly, potential risks must be balanced with benefits in all types of improved forest trees, considering the deployment schemes that will be used in space and time. In any event, deployment strategies should be designed to minimize the risks of economic losses of the stand as well as future biological losses, such as the development of resistance in pest and disease populations (e.g. Roberds and Bishir, 1997).
To help address many of these types of concerns, several countries have developed regulations and restrictions specifying the requirements of confined field testing needed before commercial release of GM plants (OECD, 2000). These requirements, necessary to reduce biological and economic risks, will undoubtedly continue to evolve, as will national laws and regulations, and other broader international agreements on biosafety, e.g. the Cartagena Protocol on Biosafety (CBD, 2000). New institutions are also surfacing to assist with critical research in the applications and policy around the use of GM trees (Burke, 2001).
Private investors have taken the lead for most investments in modern biotechnology, and in so doing have also had to manage the associated economic risks. In many situations these investment risks are protected by patents, and agreements for the use of techniques or material could then be prohibitively expensive.
In order to offset some of these concerns, the role of governments may have to expand in research and development in order to provide a flow of material and information that can be used and shared by both private and public institutions (Santos and Lewontin, 1997). The allocation of funds, whether through private or public agencies, needs to achieve a balance between building scientific capabilities and knowledge, and supporting more applied, well proven forestry technologies (Burdon, 1994). In this regard, the investment and use of any biotechnology needs to be assessed on a case-by-case basis.
Although the rapid generation turnover in crops has allowed genetic modification technology to develop quickly, the ecological ramifications in forestry will likely be much more difficult to evaluate. Due to the relatively long period a tree requires to grow to a usable size, it is likely they will encounter more environmental stresses (e.g., variable weather, pests), that could trigger unpredictable genetic responses. Long periods of testing will be required for proper evaluation under both laboratory and field conditions. Public and government acceptance of GM plants is now as dependent on biological risk assessment and risk issue management (Leiss, 1999) as it is on any technical or economic issues.
The following are few summary points and conclusions that can be drawn from the discussion above:
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14 Received March 2002. Original language:
15 This article is the updated summary of a paper published in UNASYLVA No. 204(52):52-61, while the author was at FAO under the Visiting Expert from Academic and Research Institutions Program.
16 Research Branch, British Columbia Forest Service, 712 Yates St. 3rd floor, Victoria, Canada. V8W 9C2