Forestry Research

Despite their high economic and environmental values, molecular geneticists have, until recently, largely neglected trees as a research area. This is understandable, since genetic analysis of organisms with such long reproductive cycles is frustratingly slow. Nonetheless, many biochemical reactions that are important for primary and secondary cell wall formation, and thus are determinants of wood quality, should attract the attention of molecular biologists. Indeed, certain fast growing trees, such as eucalyptus and poplar, are now being studied. Many thousands of expressed sequence tags have been sequenced and as a result, a wealth of new genes has been discovered. Transgenic trees that are down-regulated in enzymes involved in lignin biosynthesis have been generated. In this way, it has been possible to obtain poplar wood from which lignin can be more easily extracted. When applied, this might lead to a decreased use of chemicals during cellulose production for the paper industry.

By altering the degree of lignin methy-lation or by altering the levels of appropriate peroxidase enzymes, transgenic poplars with different lignin composition have been obtained. This pioneering work will hopefully attract additional researchers to molecular tree research, whose input will be required if work on tropical trees is to be initiated.

Selection of putatively superior trees, even within the genus Populus, is, however, a very long term process. Many genotypes flower only once every five or ten years. This means that screening the progeny for certain important economic traits involves a waiting period of 15 years until the tree has matured. Powerful molecular marker technologies, such as AFLP, can circumvent this problem by providing tree breeders early on with the necessary information to increase the efficiency of the analysis of the outcome of crosses. In our own work with fungal disease resistance (Melampsora larici-populina), bulk segregant analysis has identified rather efficiently a DNA fragment that is present in resistant trees but absent in sensitive trees.9 This marker is now being used in poplar breeding schemes, demonstrating the power of AFLP in breeding of trees in general.

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