While the major agricultural species are covered by recognized conservation systems, few large-scale initiatives have been taken to preserve underutilized and orphan species. However, to meet the challenges of the future, the study and protection of agricultural biodiversity must not be based solely on a limited number of species, but must be envisaged from a broad, open perspective, presenting each species as being interdependent on the others and a representative of its own specific evolutionary process.
Today, a conservation program cannot be implemented without first defining the objectives for the use of resources and for acquiring knowledge of intra- or inter-species genetic diversity. Once the objectives have been established, questions should be asked about the representativeness of genetic diversity (what should be preserved and in what quantities?) and the cost of setting up and maintaining these collections.
In situ collections consist of preserving species in their natural or human- modified ecosystems, in other words, the place in which they developed their distinctive characteristics. These collections mainly concern wild species and are often represented by the national or regional parks that protect the ecosystems as a whole. While this type of conservation represents the ideal model in that it maintains the selection pressure of its environment, its effectiveness in terms of conservation often depends on the degree to which local populations are involved in the management of the region and its resources. Moreover, it provides no protection against climate or biological risks (pathogens, plant pests, or invasive species).
Ex situ collections consist of preserving genetic resources outside of their natural habitat. This conservation method freezes the resources at the genetic level. The degree of protection of resources and their independence in relation to the natural environment is highly variable depending on the type of conservation. Whole plants may be kept in the form of field collections, arboreta, in greenhouses, or in tissue culture. Fragments of plants (meristems, embryos, tissues), which can be used to regenerate a whole plant, may be preserved at very low temperature in liquid nitrogen. Seeds are commonly held in cold storage, under controlled humidity conditions. Conserving pollen at low temperature means that a stock of haploid material that can be maintained. By conserving as much diversity as possible at lower cost, DNA banks can be used for intra- and interspecies genetic studies. Within ex situ collections, a distinction can be made between safeguarding and active or working collections, which give rise to specific activities that involve the resources stored, such as genetic diversity studies and plant breeding research.
These ex situ conservation methods are, nevertheless, reliant on human activity and on the smooth functioning of the conservation facilities and structures.
Finally, herbaria (see Chapter 4)—the first method for conserving plant species (sixteenth century)—and spirit collections are essential, especially for conducting taxonomic studies.
Although the economic cost of maintaining collections is linked to the number of accessions conserved, the issue of the number of individuals that represent diversity and ensure the security of the accession is crucial. The principle of the “core collection” may provide a response. Noirot et al. (1996) developed a method for creating a core collection based on quantitative data. This method (Principal Component Scoring) aims to include the maximum diversity from the base collection in a sample of minimum size, while avoiding redundancies.
For plant genetic resources, each conservation system has its advantages and disadvantages and often only a combination of these different systems will make it possible to optimize and to secure the conservation of resources.
In addition to the quantitative aspect (the number of species and accessions conserved), the quality of data and research programs linked to resources is now a key element in justifying the material and human investments. The value and accuracy of these data also contribute to the development of resources.
The Case of Vanilla
The genus Vanilla, which belongs to the Orchid family, includes 90–100 species depending on the author (Bory et al., 2008c). Most of these species are wild; only two of them, V. planifolia and V. tahitensis, are grown to produce commercial vanilla, with V. planifolia providing 95% of the world production. The taxonomy of vanilla is very old (Portères, 1954; Rolfe, 1896), incomplete, and still imprecise (see Chapter 1). It must therefore be thoroughly revised, especially in light of the findings of recent molecular genetics and cytogenetics research (Bory et al., 2008a, 2008b; Cameron, 2003, 2009; Schluter et al., 2007; Soto Arenas, 2003; Verma et al., 2009). For example, several recent research studies on the origin of V. tahitensis suggest that this species is the result of cross-breeding between V. planifolia and V. odorata (Besse et al., 2004; Bory et al., 2008d; Lubinsky et al., 2008b).
The species of the genus Vanilla are mainly found in natural habitats in tropical and subtropical regions of the American, African, and Asian continents. Most are threatened by the destruction of their original habitats, which is accentuated by climate change. The species V. planifolia is particularly endangered, as the primary gene pool in its region of origin (southern Mexico) is subject to considerable pressure linked to deforestation and the overexploitation of natural resources (Soto Arenas, 1999). In secondary diversification zones such as the islands of the Indian Ocean, and especially Réunion—the point of entry for the species into this region in the nineteenth century—there is considerable intraspecies homogeneity, indicating that cultivation may rely on a very restricted genetic base, which probably developed from one single individual through vegetative reproduction. Molecular studies have confirmed the very low level of genetic diversity in the vanilla plants cultivated throughout the world (V. planifolia) (Bory et al., 2008d; Lubinsky et al., 2008a; Minoo et al., 2008a). The vegetative reproduction process, which is predominant for the species of vanilla grown, does not make it possible to maintain and extend the gene pool. Nevertheless, an interesting phenotypic diversity is observed, which may be explained by the accumulation of somatic mutations, by the possibility of natural seed germination in the case of sexual reproduction, but also by the variable ploidy level that can be found in cultivated vanilla species (see Chapter 2). However, due to varietal homogeneity, vanilla cultivation is particularly vulnerable to environmental hazards, such as climate change and the emergence of plant pests.