Introduction to the topic

Risk assessment and risk management of transgenic trees

by Dr. Sofía Valenzuela A., Biotechnology Center and Forest Science Faculty, Universidad de Concepción, Concepcion, Chile. E-mail: sofvalen@udec.cl

The high demand of wood for industrial, heating, structural wood and fuel will require that in a short term time the area of forest plantations should be increased. In comparison to agricultural crops, trees planted for wood production are still undomesticated plants, having an enormous genetic potential that could be expressed in valuable new varieties. Biotechnology has been used as a tool for improving trees in the last years, the first genetically modified (GM) tree being developed in 1988. Traits under study for the development of GM trees include improving wood quality (lignin and cellulose amounts), flowering control, disease resistance and stress tolerance. In fruit trees, the main traits under study include virus resistance and fruit quality.

Some specific characteristics of trees include: large population size, many years before flowering, complex ecological backgrounds, low domestication, perennials, wind pollinated. These issues raise concerns regarding the introduction of GM trees into the environment, especially with traits which can give a better fitness, as high-growth. At a commercial level, two cases of environmental release of GM trees have occurred, GM papaya in Hawaii in 1997 and GM poplar in China in 2002 have been reported.

To date, no risk assessment (RA) studies which predict with any certainty the impact of releasing GM trees on native biodiversity has been reported. The main issue that has been discussed is gene flow, but little research has been done on the impacts that the transgene(s) might have on fitness or other ecological characteristics. Knowledge of gene flow in forest trees is still unsatisfactory due to continued shortcomings of available markers, inherent limitations of statistical models. Ecological risks from non-native species and their spread is known to be unpredictable, and if it occurs can have very significant effects. A sufficient number of field studies in diverse environments need to be conducted to determine if the physiological and fitness modifications are significant or not. These field trials need to be conducted for several years and in environments (sites), since there is a strong genotype x environment effect on trees that can affect fitness.

Currently, there are several GM-tree species that are herbicide tolerant and or have been transformed using marker genes, which have already been tested at field trials. The development of GM trees has increased in the last years, having more than 200 field trials involving at least 15 forest species. However, traits with large economical value in forestry as stress tolerance, low lignin and high cellulose levels and others will require the introduction (or suppression) of many genes. Therefore transformation will include the introduction of several genes, in order to obtain the trait of interest.

Since trees are long-lived, often producing copious amounts of pollen and seeds and in some cases they multiply asexually. Some aspects of risk management of GM trees that call for further consideration include the following: 1. Flowering control: sterility is one way of controlling the spread of transgenic trees to surrounding populations of related trees. In some species, however, more seed or fruit production might be desired, such as those with high wildlife value. Flowering control is, thus, a higher priority research item than is sterility. 2. Isolation of transgenic populations: establishment of transgenic plants in an environment far away from their relatives in order to avoid introgression of modified plants with indigenous populations. 3. Establish refugia or connecting corridors of stands of non-transformed trees when designing plantations. This strategy is a combination of factors associated with the maintenance of unaltered populations of trees in the midst of plantations that have been engineered for selected morphological and physiological properties.

Despite the differences between agricultural crops and trees, the general principles and methodologies for risk assessment as described in Annex III of the Cartagena Protocol can also be applied to GM-trees. The framework for RA can be used to address specific issues raised by trees. The biosafety issues associated with transgenic trees will require that in-depth analysis is carried out on specific traits.

References provided by the author

Balocchi C, Valenzuela S (2004) Introduction to GMOs and Biosafety in Forestry. In: Kellison R, MCcord S, Gartland K (eds.) Proceedings of the Forestry Biotechnology Workshop, Global Biotechnological Forum, 2-5 March 2004, Concepción, Chile, p. 85-96. (reprint)

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