The dramatic advances in molecular genetics over the last few years have provided workers involved in the conservation of plant genetic resources with a range of new techniques for their work. For the first time techniques are available to analyse variation in plants and animals at the DNA level. Differences in gene sequence can be directly observed and described, a degree of precision previously impossible to achieve. Many of the techniques that have been developed have already been used to study the extent and distribution of variation in species genepools and to investigate evolutionary and taxonomic questions. They have also shown their value in studies of accession identity and for the detection of novel useful variation. So far, much of the work on the development and use of molecular techniques has been carried out in developed countries. There are now a number of laboratories in developing countries that have begun to carry out their own programmes but the bulk of the expertise, facilities and capacity remains in the developed world. There is a great need to expand the facilities available in developing countries where much of the genetic diversity that can be examined using molecular techniques is to be found. The aim of the International Plant Genetic Resources Institute (IPGRI) is to strengthen the conservation and use of plant genetic resources worldwide with special emphasis on the needs of developing countries. Working in partnership with national programmes, research institutions and other organizations, it undertakes research and training and seeks to provide technical advice and information. In October 1995, IPGRI organized a small workshop on the use of molecular techniques in the conservation of plant genetic resources. One area of discussion was the considerable range of different molecular techniques available and the ways in which they could best be used. Deciding on which technique would be most appropriate for particular investigations is not always straightforward and depends on a range of different factors including the nature of the problem, the biology of the species and the resources available. The participants at the Workshop recommended that IPGRI should prepare a publication which provided users with some guidance on the different molecular genetic techniques currently available and their use in addressing some of the key questions faced by plant genetic resources conservation workers. A number of participants have therefore collaborated with IPGRI staff to prepare this publication. The publication attempts to provide a brief overview of currently available techniques and to outline some of their strengths and limitations. It also provides a framework to assist users in identifying what technique(s) might be most appropriate for their own needs. It is not intended as a laboratory manual of the techniques or as a substitute for the many excellent discussions of the strengths and weaknesses of individual methods that can be found in the literature. Rather, it is a broad survey of the main features of the different techniques and of the factors that conservation workers should bear in mind when initiating a molecular genetic based investigation. Molecular genetics is a fast-moving field and new techniques are likely to be developed in the future which will have their own strengths and limitations. Users of this publication will want to be able to consider these as well and it is hoped that the principles identified in this publication are sufficiently general to enable them to do this. Although the power of molecular techniques provides tremendous new opportunities for conservation workers, they should not be seen as a substitute for other agromorphological or biochemical studies that provide users with the information they need on the resources conserved. Indeed one of the main objectives of current work should be to link these different components together to provide a more complete understanding of the diversity available and the ways in which it can best be used to enhance agricultural and forestry production and sustainable development.

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