Three fundamental objectives for the conservation of plant genetic resources for food and agriculture (PGRFA) can be identified in the ongoing discussion (Virchow, 1999; FAO, 1998):
• Ensure future utilization through long-term ex situ conservation, which conserves PGRFA in their present constellation for future generations to come.
• Support adaptation of PGRFA to changing environmental conditions through long-term in situ conservation, which exposes genetic resources to ecological pressure enforcing natural changes and permitting continued coevolutionary development, as well as adoption via selection activities by farmers.
• Facilitate convenient access through storage activities that support the supply of genetic resources as raw material. Stored collections need to be easy accessible for ongoing breeding programs by scientists, farmers, and interactive groups of farmers and scientists.
The term "ex situ conservation" is applied to all conservation methods in which the species or varieties are taken out of their traditional ecosystems and are kept in an environment managed by humans. Starting with the collecting activities of N. I. Vavilov, most conservation efforts for agricultural crops have until recently involved the use of ex situ conservation; particularly in the form of seed genebanks. Great emphasis was placed on germplasm collecting during the 1970s and 1980s. As a result, the conservation of agricultural plants is presently dominated by ex situ collections. Defined as the conservation of plants in their ecosystems, "in situ conservation," has been traditionally used for the conservation of forests and of sites valued for their wildlife or ecosystems (FAO, 1998). In recent years, however, the need for in situ conservation of PGRFA has been increasingly emphasized, above all at the United Nations Conference on
Environment and Development in 1992 (UNEP, 1994) and during the preparatory process for the International Technical Conference on PGRFA (FAO, 1998).
Both terms, ex situ as well as in situ conservation, originate from the conservation activities of wild plants and animals. These terms are now commonly used in the context of the conservation of PGRFA, but do not fit this application perfectly. By their very nature, PGRFA can only be maintained by human management, i.e., through a process of selection for cultivation in farmers' fields. Consequently, strictly following the terminology, all PGRFA are already in a state of ex situ management. On the other hand, in situ conservation for PGRFA is not possible, sticking to the terminology in the narrow sense, because domesticated plants do not have a natural habitat per se, and if left alone in the natural habitat of their wild relatives, they will have very little chance of survival. Therefore, the terminology adopted in this chapter is applied in a broader sense, i.e., ex situ conservation is defined as the management of domesticated plants or parts of them, outside of their common surroundings, mainly the farm as the agricultural production unit. Following the broader framework of definition, in situ conservation is defined as all activities to conserve PGRFA in their common surroundings, including the "on-farm management" of PGRFA. As defined in the Convention on Biological Diversity, in situ conservation of PGRFA ". . . means . . . the maintenance and recovery of.. . domesticated or cultivated species, in the surroundings where they have developed their distinctive properties" (UNEP, 1994).
Experience from the existing in situ and ex situ conservation methods demonstrate that agrobiodiversity cannot be completely conserved by any single method. It should not be surprising that neither method is able to realize all the expected objectives of plant genetic resources conservation.
The two different concepts of conservation have been developed by the major actors involved in the various types of conservation activities: ex situ conservation—enforced and promoted by governmental and intergovernmental organizations as well as the private seed sector—has been managed for the conservation of those crops, which are mainly of interest at the global level. In situ conservation has been promoted mainly by NGOs, and handles important regional or local food crops, as well as crops which are not suitable for genebanks.
The limitations of ex situ conservation can be summarized as follows:
• Because of the current state of technology, many important species with unorthodox seeds cannot be stored in seed genebanks. Consequently, such species are underrepresented in germplasm collections.
• Ex situ storage methods do not guarantee long-term conservation without any negative impacts on the diversity of the plant genetic resources. A genetic shift due to insufficient and inappropriate regeneration, storage, health care, and existing capacities results in a decline in the genetic variation that existed in the original collection sample.
• Because of the conservation method, genetic resources conserved ex situ are not exposed to natural and artificial pressure and cannot, therefore, be expected to evolve and adapt to environmental changes.
Although few studies examine the potential of on-farm tin situ conservation, the known limitations of this form of conservation are (Virchow, 1999):
• If PGRFA conservation through on-farm management is implemented by minimizing the area allocated to each variety to be conserved, there is a risk that some allelic diversity will be lost in the limited population.
• Cultural and socioeconomic factors are important for the development of diversity at the local level, but they are related to ecological, social, and technological development. Therefore, the future interest of local communities and individuals in conservation activities cannot be taken for granted.
• The promotion of in situ conservation of PGRFA is pointless without a very long time horizon of at least 50 to 100 years, which increases the risk for the unsuccessful implementation of conservation plans.
Given these limitations, the main advantages of in situ over ex situ conservation can be described as follows (Virchow, 1999):
• In situ conservation of PGRFA, as a dynamic form of plant genetic resources management, enables the processes of natural and artificial selection to continue. Consequently, despite the loss of some allelic diversity, on-farm management promotes the development of diversity (seen from a perspective of approximately 100 years).
• It allows the possibility of conserving a large range of potentially interesting alleles.
• It facilitates research on species in their natural habitats.
• It increases protection of associated species, which—in spite of their having no obvious economic value—may contribute to the functioning and long-term productivity of ecosystems.
• In situ conservation is especially desirable for crops that do not receive sufficient attention from the formal sector, i.e., government and intergovernmental organizations.
• In situ conservation may contribute to an agricultural development while conserving diversity. Linking the management of PGRFA to the improvement of landraces through breeding may be an appropriate strategy for improving farmers' livelihoods in marginal areas as long as there are no economic alternatives.
The links between ex situ and in situ conservation have, in the past, been generally limited to the transfer of germplasm samples from the farmers to the ex situ collections. This one-way traffic of information and goods clearly shows the present suboptimal utilization of the conservation methods. There is far more potential for interaction among the various actors to the mutual benefit of the whole conservation system. Hence, an efficient combination of ex situ and in situ conservation methods is important to improve overall conservation efficiency.
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