General Concepts in Plant Germplasm Conservation

Plant germplasm is in reality biological information that is passed down through generations in an unbroken chain (Wilkes, 1988). Once this chain is broken, for instance by the destruction of a particular habitat and the consequent loss of certain gene pools, that unique information is lost forever. This has led to the necessity of pro- tecting and preserving plant genetic diver- sity for current and future use.

Habitat or ecosystem destruction or alteration throughout the world has resulted in the loss of increasingly large numbers of plant species, reducing genetic diversity and threatening the availability of plant germplasm needed for future genera- tions (World Wide Fund for Nature and International Union for Conservation of Nature and Natural Resources, 1994–1997). Consequently, preservation of the genetic diversity represented in all the plant ecosystems throughout the world has become a major issue of international con- cern (Holden and Williams, 1984; Brown et al., 1989; Holden et al., 1993; National

© CAB International 2007. Citrus Genetics, Breeding and Biotechnology (ed. I.A. Khan) 45

Research Council, 1993; Food and Agriculture Organization of the United Nations, 1996). Although in some cases habitat loss may be due to natural events or ‘catastrophes’, in most cases habitat loss is due to human activities. In historical per- spective, McNeely et al. (1995) have sum- marized these losses as paralleling the human hunter-gatherer, farming, urban and modern high-energy phases. These phases of course greatly simplify the actual causes of (among many others) population growth, domestication of fi re, pollution, exploita- tion of natural resources, conversion of nat- ural habitat to agricultural or urban uses, deforestation, etc. The reader is referred to McNeely et al. (1995) for an overview, and to the World Wide Fund for Nature and International Union for Conservation of Nature and Natural Resources volumes (1994–1997) for more specifi c information on particular localities.

Ideally, genetic resources should be conserved in situ. However, the factors mentioned above make maintenance of genetic resources in situ somewhat precari- ous. This is especially true today when technology makes possible the loss or alter- ation of large areas of habitat in very short time frames. Ex situ conservation is there- fore often necessary to save or conserve genetic resources. Genetic materials may be lost through disease, weather, etc., and so ex situ collections should be maintained in many cases even when there is not an immediate threat of habitat loss. Ex situ collections are also more accessible for researchers for characterization, evalua- tion and utilization. Maintenance of germplasm in a disease-free state is also desirable, and this is often possible only in ex situ collections. Unfortunately, losses can also occur in ex situ plant collections because of inadequate maintenance, natural disasters, etc. For more detailed informa- tion on general aspects of plant genetic con- servation, the reader is referred to Given (1994).

Plant germplasm conservation by humans can be considered to have started in some ways with early human beings,

who saved seeds of favoured varieties for food, feed, fi bre, and medicinal and reli- gious purposes, developed grafting (which allowed perpetuation of specifi c clones) and managed natural resources. Although with a small and technologically limited population, early human beings had a lim- ited impact in these areas, they still must have exerted some pressure upon the par- ticular varieties or types of plants con- served. Plants without obviously utilizable properties would probably not have received recognition as types being worth conserving. As humans increased in popu- lation and technology, this viewpoint led to the problems noted above.

Involvement of governmental bodies in germplasm conservation might be consid- ered to have started long ago with royal gar- dens, woods, etc. However, as with the early humans and agriculturally oriented societies in general, plants were selected for inclusion in these areas based upon obvi- ous traits, such as beauty, hunting habitat, etc. With the development of scientifi cally based agriculture, some agricultural types of plants were conserved almost by acci- dent as types for use in breeding pro- grammes and other investigations. This did lead in some instances to substantial amounts of crop plant genetic resources being conserved, but it was not until the latter half of the 20th century that govern- ments began making concerted efforts to conserve crop plant germplasm. Perhaps it was Vavilov, the seminal fi gure in plant genetic resource conservation, who fi rst recognized the importance of making a con- centrated effort to conserve not only crop species but also their wild relatives in ex situ gene banks. Programmes or systems with this goal were developed in different countries and in some cases by intergovern- mental entities such as the centres of the Consultative Group on Interna- tional Agricultural Research (CGIAR) and some establishments of the Food and Agriculture Organization of the United Nations (FAO).

An example of government-sponsored conservation of plant genetic resources is

the United States Department of Agriculture-Agricultural Research Service (USDA-ARS) National Plant Germplasm System (NPGS) in the USA, which had its origins in the 1970s (Shands et al., 1988; White et al., 1989; National Research Council, 1991; Shands, 1995). Efforts towards conservation of the so-called ‘clonal’ crops (such as citrus) began later, in the mid- to late 1980s (Brooks and Barton, 1977; Westwood, 1989). Although the USA has one of the largest and most advanced systems for plant germplasm conservation, it is ironic that, with a few notable excep- tions such as maize, North America is not home to important crop plant species. Consequently, most of the materials main- tained by the NPGS are acquired from other countries by exchange, plant exploration, etc.

In recent years, plant germplasm con- servation and utilization has become com- plicated by such factors as the Convention on Biological Diversity, Globalization, Intellectual Property Rights, Indigenous Rights, Farmer’s Rights, etc. Discussion of these controversial and political areas is beyond the scope of this review, and there is no current one-volume overview of these intertwined and complex competing rights. Some very general information on these areas as well as on plant germplasm conservation in general can be gleaned from popular writings such as Fowler and Mooney (1990), Busch et al. (1995) and Raeburn (1995). Perhaps the best and most complete information was avail- able in the now-defunct magazine Diversity. Other sources are various publications and other disseminations from the International Plant Genetic Resources Institute (IPGRI) < https://www.ipgri.org/> (formerly the International Board for Plant Genetic Resources, IBPGR) and the FAO < https://www.fao.org>. Since most of the international political nego- tiations regarding plant genetic resources take place under the auspices of these enti- ties, these webpages are perhaps the best place to start for up-to-date basic informa- tion.