Feb 12, 2010

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Aims of genetic engineering in woody plants

New traits in woody plants

Quickly growing trees with high yields, trees with less lignin for simpler production of paper, apples that are resistant against the dangerous fire blight pathogen, fruits that keep longer and are simpler to store - the list of the breeding aims with wood is long. For about the last 20 years gene technological methods have been pursued.

In comparison with genetically modified agricultural crops, which are already grown commercially throughout the world, transgenic woody plants have so far played only a minor role. One of the reasons for this is that they have a very long life time. Many years or decades of research are necessary to determine whether a genetic modification shows the desired effect and remains stable with time. Because of the long lifetime and the complex and comparably little explored propagation avenues, the risks of a further spread of the foreign gene in woody plants is estimated to be particularly high.

It will probably be another five to ten years before the research and development is far enough for the first genetically modified trees can be commercially used in Europe. In the USA there is already market approval for papaya (since 1996) and plums (since 2007) with gene technology-generated virus resistance.

Currently, gene technological approaches are being pursued for fruit and ornamental shrubs and trees in large-scale plantations.

Wood as an energy plant

Woody plants are playing an increasingly important role in the use of biomass for energy generation. Studies are therefore being carried out on rapidly growing trees, such as poplars or eucalyptus, which can deliver more wood and also grow in colder regions.

Wood is also gaining increasing importance as the raw material for bioethanol. For this the plants have to be genetically modified so that they produce enzymes that can breakdown the cellulose into fermentable sugars.

Armed against pests

Of particular interest, also for woody plants, is to make the plants resistant against diseases and herbivores. For forest plants, this primarily concerns resistance against insects and fungi, for fruit trees resistance against bacterial pathogens such as fire blight, fungal diseases such as apple scab and mildew, as well as viruses.

Resistance against herbicides is, in contrast, not so important for woody plants since clearance of weeds plays a lesser role here than in agriculture. Herbicides are used, for example, against too strong undergrowth with young trees.

Improvement of product quality

When processing wood to paper, the lignin has to be separated out in complex and environmentally unfriendly processes to obtain the pure cellulose fibres. The paper industry has therefore a strong interest in trees with less lignin or a modified lignin that is easier to separate from the cellulose. Gene technological approaches through which trees would deliver longer cellulose fibres are also being followed.

With fruit trees, genetic modifications are aimed, for example, at delaying the ripening of the fruit or improving its shelf life. Improving the quality of the fruit is also an aim, such as the increased production of flavonoids in apples, which are said to have a health-promoting effect.

Trees for extreme locations

Normally, trees are well adapted to their location. But increasingly trees are expected to flourish in difficult locations, such as places where there is a high burden of air pollution. In plantations, trees have to be grown in locations that may not be their normal habitat, i.e. depending on the given conditions, they need to be tolerant to, for example, drought, salinity or frost.

Trees for reclamation of burdened soils

Trees can be used to remediate soils burdened through previous mining or chemical industry locations. Gene technology could be used to help improve the natural ability of trees to detoxify heavy metals, through chemical reactions, and to store these in their leaves.