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21 Conservation of Crop Genetic Resources - NIGEL MAXTED AND DAVID R. GIVEN
414 • The Cultural History of Plants
To increase the genetic diversity of U.S. corn, the Germplasm Enhancement for Maize (GEM) project seeks to
combine exotic germplasm, such as this unusually colored and shaped maize from Latin America, with
domestic corn lines. Photo by Keith Weller. ARS/USDA.
biotechnologists do when they introduce new genes into crop varieties. Both traditional farmers
and plant breeders need continued access to genetic diversity if they are to make progress in their
ongoing battle with evolving pests and diseases, and thus maintain food security.
The economic impact of breeding disease resistance in a crop can be high. For example, the use of
Hessian ﬂy resistance in wheat in the U.S.A. saved $17 million in a single year (Bouhssini et al. 1998).
In contrast, however, the consequences of lack of genetic diversity in crops can be devastating, as
shown by the often-quoted case of potato blight in Ireland in 1845. An infection of late potato blight
(Phytophthora infestans) wiped out the potato crop in Ireland, leading to the Great Potato Famine of
1845–1849, and the starvation and emigration of millions of people. The existing varieties of potato
at that time had no resistance to P. infestans. Resistance was subsequently found by the 1870s in the
Chilean subspecies of Solanum tuberosum subsp. andigena and in several wild potato species, particularly Solanum demissum from Mexico (Hawkes, Maxted, and Ford-Lloyd 2000).
See: Roots & Tubers, pp. 63–5
No country is sufﬁciently rich in native genetic diversity to make it independent of other regions
of the world. In Brazil, for example, which has an abundance of plant-life, two-thirds of its calorie
consumption is based on crops originating from other continents (see Table 21.1).
TABLE 21.1 Source of Plant-Derived Calories Consumed
in Brazil (Crucible Group 1994)
Share of Plant-Derived
Center of Origin
Conservation of Crop Genetic Resources • 415
Of course in addition to their direct economic use by humans, plants play a pivotal role in natural ecosystems and contribute to the functioning of the biosphere, as well as having aesthetic and
recreational value; each is a signiﬁcant impetus to conservation. The conservation of wild plants,
with these important roles, is considered in the previous chapter.
Gene Pool Concepts
The history of human exploitation of plants is as long as human evolution itself, stretching from
hunter-gatherers in pre-agricultural societies to targeted exploration and collection by European
colonists in Asia and South America. But it was the Russian botanical geneticist Nikolai I. Vavilov
who, in the early years of the 20th century, realized the importance of conserving the total genetic
diversity contained within any crop complex (such as peas)—not only diversity within the crop
species itself, but also that found in its wild relatives—to make the full range of genetic diversity
available to plant breeders. This total range of genetic diversity is known as the crop gene pool. This
concept was developed and formalized by Harlan and de Wet (1971) (see Figure 21.1).
• Primary gene pool (GP-1): all cultivated, wild, and weedy forms of a crop species. Hybrids
among these taxa are fertile, and gene transfer to the crop is simple and direct. This pool
of taxa is often referred to as a biological species.
• Secondary gene pool (GP-2): the group of species that can be artiﬁcially hybridized with
the crop, but where gene transfer is difﬁcult. Hybrids may be weak or partially sterile, or
their chromosomes may pair poorly during meiosis.
• Tertiary gene pool (GP-3): including all species that can be crossed, though with some
difﬁculty (e.g., requiring in vitro hybrid embryo culture), and where gene transfer is
impossible or requires radical techniques (e.g., radiation-induced chromosome breakage).
Figure 21.1. Schematic diagram of gene pool concept (Harlan and de Wet 1971).
416 • The Cultural History of Plants
TABLE 21.2 Common Features of Crops, Crop Progenitors and Wild Relatives.
Large fruit, seed, or ﬂower size
Very ﬂavorsome fruit or seed
Very nutritious fruit or seed
Highest protein content
Highest oil content
Aesthetically pleasing color
combinations in ﬂowers and
Fruit, seed, or ﬂower size larger
than average for wild species
Fruit or seed slightly more
ﬂavorsome than average wild
Fruit or seed slightly more
nutritious than average wild
High protein content
High oil content
Unusual color combinations in
ﬂowers and fruits
Average fruit, seed, or ﬂower size
for wild species
Average ﬂavor of fruit or seed for
Low protein content
Low oil content
Drab color combinations in
ﬂowers and fruits
Vicia faba ssp. paucijuga, Narbon
bean (Vicia narbonensis)
Other Hordeum species
Vicia bithynica and other vetch
Average nutritional value of fruit
or seed for wild species
Barley (Hordeum vulgare)
Faba bean (Vicia faba)
If this concept is applied to barley as an example, Hordeum vulgare and its progenitor, H. spontaneum,
would belong to GP-1, H. bulbosum to GP-2, and all the other species of the genus to GP-3. The
highest value would be ascribed to the GP-1 species, then GP-2, and ﬁnally GP-3. This kind of priority setting can be reﬁned, as some species within a given gene pool may be more likely to harbor
desired traits. In general, the wild progenitors of crops are the most promising source of new genes,
because they often share characteristics with the crop plant that are lacking from species in the secondary and tertiary gene pools (GP-2 and GP-3).
From his observations of crop gene pools, Vavilov also noted similar patterns of variation
between crops and their wild relatives for each gene pool. In other words, wild relatives from
another genus sometimes showed some features of domestication (large seed, lack of fruit shattering, nutritious fruits, etc.) that were absent from most related wild species (see Table 21.2). He
noted this parallelism in domestication characteristics in many different crop complexes (for example, vetches, lentils, and peas) and this forms the basis of his Law of Homologous Series (Vavilov
1922). The importance of Vavilov’s law is that it has predictive value, in that if one crop plant is
found with a particular trait, then this same desirable trait is likely to be found in the gene pool of
unrelated crop species. There is an obvious tie-in here with contemporary views of phylogenetic
evolution and synteny.
The gene pool concept is, by deﬁnition, crop- or single species-centered, in that there is always
one taxon in GP-1A. However, a single species may conceivably be in GP-1 for one crop, GP-2 for
another and GP-3 for a third. Expanding on Harlan and de Wet’s work, Maxted, Ford-Lloyd, and
Hawkes (1997) have developed the concept of the “gene sea,” where each species is at the centre of
its own gene pool, but all individual gene pools are interrelated in one expanse of genetic diversity,
as shown in Figure 21.2.
Thus, species that are present in multiple overlapping gene pools within the gene sea would be
given the highest priority for conservation, because they would better represent the breadth of plant
genetic diversity in the lowest number of populations or accessions.
Conservation of Crop Genetic Resources • 417
Figure 21.2. Schematic diagram of a segment of the gene sea (Maxted, Ford-Lloyd, and Hawkes 1997).
The Threat to Plant Genetic Resources
Plant genetic resources are increasingly threatened at the ecosystem, species, and genetic levels,
largely as a result of human activities. For example, in the case of crop plants, the proportion
of the wheat crop in Greece contributed by landraces or old, indigenous varieties declined
from 80 percent in 1930 to less than 10 percent in 1970. In China, nearly 10,000 wheat varieties
were in use in 1949, but only 1000 were still in use by the 1970s (FAO 1998). In Cambodia,
unique rice varieties were lost in the 1970s when war disrupted agricultural production. Stored
seed in the national gene bank was eaten or rotted, and numerous landraces would therefore
have died out, were it not for the duplicates preserved in the International Rice Research Institute (IRRI) gene bank in the Philippines. In Mexico and Guatemala, urbanization has displaced some of the populations of teosinte (Zea mexicana), the closest relative of corn, and
these populations have also suffered genetic pollution from genetically modiﬁed corn (Quist
and Chapela 2001).
It is likely that virtually all plant species are currently suffering loss of genetic variation to varying degrees: it was estimated that 25 to 35 percent of plant genetic diversity could be lost over the
next 20 years (Maxted, Ford-Lloyd, and Hawkes 1997).
National and international agencies must deal with a paradoxical confrontation between conservation and development. Plant breeders throughout the world are rightly engaged in developing
better and higher-yielding cultivars of crop plants. This involves the replacement of genetically variable, lower-yielding landraces with products of modern agriculture, which are much more genetically uniform. Thus, genetic uniformity is replacing diversity. These same plant breeders are,
however, dependent upon the availability of a pool of diverse genetic material for success in their
work, and thus are unwittingly causing the genetic erosion of plant diversity that they themselves
will need in the future—hence the paradox. Of course, replacement of traditional landraces by
modern cultivars is not the only cause of genetic erosion or loss of genetic diversity; other changes
in farming systems, the intensiﬁcation of production systems, overexploitation, introduction of
exotic cash crops, human socio-economic changes and upheaval (e.g., extinction of tribal cultures,
urban sprawl, land clearances, food shortages), as well as both natural and man-made calamities
(e.g., ﬂoods, landslides, or wars) have all acted against the retention of socio-economically important biodiversity.
418 • The Cultural History of Plants
TABLE 21.3 Estimated Annual Markets for Genetic
Resources Products (ten Kate and Laird, 1999)
Cosmetics & Personal
(US $ billion)
Estimate (US $
Plant genetic resources cost/beneﬁt analysis
The economic beneﬁt of plant genetic resources use has recently been reviewed by ten Kate and
Laird (1999). Although it is very difﬁcult to estimate precisely the annual global market value of
plant genetic resources, they suggest a range of ﬁgures between US $500 to $800 billion; the breakdown of ﬁgures is given in Table 21.3. The use of wild species by local communities should not be
underestimated; for example in Tanzania in 1988, it was estimated that the value of all wild plant
resources to rural communities, whether through subsistence consumption or sale, was more than
US $120 million (8 percent of agricultural GDP) (FAO 1998).
Of the industries that depend on diversity, agriculture remains by far the largest. Phillips and
Meilleur (1998) estimate that endangered food crop relatives have a worth of about US $10 billion
annually in wholesale farm values. Various studies, mostly conducted on cereals, have estimated
that more than 50 percent of the increase in crop production has been due to the improvement of
crop cultivars, and such improvement is brought about by transferring desirable genes/traits to
crops from landraces and other more distant germplasm sources. Thus, the transfer of dwarﬁng
genes from Japanese semi-dwarf material to U.S. and Mexican wheat stocks led to the revolution of
wheat production in the world during the 1960s and 1970s (see Grains, pp. 45, 53). This so-called
“green revolution” helped food-deﬁcient countries like India become food sufﬁcient, and ultimately even net exporters within a short period of 10 years.
The transfer of genes for high sugar content to the tomato (Lycopersicon esculentum) from its wild
relative (L. chmielewskii) has generated an additional income of US $5 to $8 million per year for the
tomato industry (Iltis 1988). Although precise estimates of the global value associated with the use of
plant genetic resources do vary, it is clear that plant genetic resources have a real and substantial value.
However, there is a cost involved in conserving this diversity. Using the FAO (1998) ﬁgure of 6.1 million accessions in world gene banks, and using the estimates of Smith and Linington (1997) for the cost
of obtaining the material (US $597 each) and incorporation of the material into the gene bank (US $273
each), we then have a total cost of US $5.3 billion for collecting and conserving the world’s germplasm in
gene banks. Even the cost of maintaining existing ex situ gene bank accessions is not insigniﬁcant considering the commitment to conserve is open-ended. Taking Smith and Linington’s (1997) estimates of the
annual cost of maintaining an accession of US $5 each, then for 6.1 million accessions the running cost is
US $30.5 million per year. We have no estimate of in situ expenditure, but for the United States at least, it
has been estimated that more than 98 percent of all conservation expenditure is spent on in situ activities
Conservation of Crop Genetic Resources • 419
related to wild species (Cohen et al. 1991). Although these ﬁgures are relatively high, they are small compared to the annual market for genetic resources use. Therefore simple cost/beneﬁt analysis clearly indicates humans are very short-sighted to carelessly oversee loss and threat to plant genetic diversity.
International treaties and plant genetic resources
Recognition of the fundamental importance of these issues was highlighted at the United Nations
Conference on Environment and Development (UNCED) held in Rio de Janeiro, Brazil in 1992, and
has been enshrined in the resulting Convention on Biological Diversity (CBD). Its objectives are:
… the conservation of biological diversity, the sustainable use of its components and the fair and
equitable sharing of the beneﬁts arising out of the utilization of genetic resources, including by
appropriate access to genetic resources and by appropriate transfer of relevant technologies, taking into account all rights over those resources and to technologies, and by appropriate funding
The CBD was the ﬁrst global treaty that linked the conservation of biodiversity to sustainable utilization. It represents a milestone in biodiversity conservation thinking, reﬂecting international acknowledgement of the loss of our biological resources, their role in human development and wealth creation,
and the urgent need for conservation action and sustainable exploitation. The CBD is now recognized
as the primary guiding framework for the conservation, management, and use of biodiversity.
More speciﬁc reference to plant genetic resources is made in the International Treaty on Plant
Genetic Resources for Food and Agriculture (ITPGRFA), agreed by 116 countries in Rome in
November, 2001. The International Treaty is in harmony with the CBD, and many of its articles
make explicit propositions in the CBD, especially as regard Farmers’ Rights—recognizing the contribution that the local and indigenous communities and farmers of all regions of the world have
made to the conservation and development of plant genetic resources. Farmers’ rights are equated
with plant breeders’ rights. It is a legally binding international agreement, which will come into
force when ratiﬁed by at least 40 states. The objective of the ITPGRFA was expressed in Article 1.
The objectives of this Treaty are the conservation and sustainable use of plant genetic
resources for food and agriculture and the fair and equitable sharing of the beneﬁts arising
out of their use, in harmony with the Convention on Biological Diversity, for sustainable
agriculture and food security (www.fao.org/ag/cgrfa/itpgr.htm#text).
It takes into consideration the particular needs of farmers and plant breeders, and aims to guarantee the future availability of the diversity of plant genetic resources for food and agriculture on
which they depend, and the fair and equitable sharing of the beneﬁts.
These Treaties both provide a broad framework for plant conservation linked to sustainable and
equitable use of resources, but they lack any speciﬁc strategy for achieving their objectives. The
CBD’s Conference of the Parties, who are charged with implementing the CBD, adopted a Global
Strategy for Plant Conservation (GSPC) at its seventh meeting in November, 2001. GSPC provides
the necessary speciﬁc conservation targets that are to be achieved by 2010, several of which relate to
plant genetic resources (the full list of targets is provided in Conservation of Wild Plants, p. 402):
• Thirty percent of production lands to be managed consistent with the conservation of
• Seventy percent of the genetic diversity of crops and other major plant genetic resources to
420 • The Cultural History of Plants
• No species of wild ﬂora is to be subject to unsustainable exploitation resulting from international trade
• Thirty percent of plant-based products to be derived from sources that are sustainably
• A reversal of the decline of plant resources that support sustainable livelihoods, local food
security and health care
• Every child to be aware of the importance of, and the need to conserve, plant diversity
• The number of trained people working with adequate facilities in plant conservation and
related activities to be doubled
• Networks for plant conservation activities established or strengthened at international,
regional, and national levels
Even more detailed targets are being used by many national governments and regions—for
example, the European Plant Conservation Strategy.
Where Are Plant Genetic Resources Found?
Plant biodiversity, as has been seen in the chapter on conservation of wild plants, is not evenly
distributed across the surface of the Earth. A similar picture of uneven geographic distribution
also emerges for that of plant genetic resources. Vavilov developed a concept of centers of diversity for crop plants, where crop gene pools were focused. Although his belief that all of these were
centers of crop domestication is no longer accepted, all are still recognized as important centers
of diversity. These were eight, generally mountainous areas, situated in tropical or sub-tropical
I Chinese Center: Western and Central China—millets, beans, onion, radish, cabbage, fruit
trees, as well as plants producing oils, spices, medicines, and ﬁbers
II Indian Center: India, Indo-Malaya, Indo-China, Burma, and Assam—rice, chickpea,
beans, many tropical fruits (including Citrus species Musa, Mangifera, etc.); oil-producing
species, ﬁbers, spices, stimulants, and dye plants; Saccharum
III Inner-Asiatic Center: Northwestern India, Afghanistan, Tadzhikistan, Uzbekistan, and
western Tien-Shan—wheat, peas, cabbage, lettuce, sesame, cotton, various vegetables and
melon species, spice crops; fruit and nut trees
IV Asia Minor Center: Transcaucasia, Iran, Turkmenistan, and Anatolia—wheat, rye, oats,
chickpeas, lentil, vetches, peas; alfalfa, clover, and sainfoin; melons; vegetables; fruit crops,
including Malus, Pyrus, Punica, Ficus, Vitis, Pistacia
V Mediterranean Center: Mediterranean countries—Forage and vegetable species; various
oil-producing plants and spices; olive, beets, cabbages, onion, asparagus, lettuce, parsnip;
ethereal oil species and spices
VI Ethiopian Center: Ethiopia—wheat, barley, peas and beans, lupins, teff, ﬁnger millet, coffee,
banana, and sorghum
VII South Mexican and Central American Center: South Mexico and Central America—
corn, beans, marrow, sweet potato, peppers, cotton, and tobacco
VIII South American Andean Center: Peru, Ecuador, and Bolivia—Potato and other tuberous
crops, some fruit crops, lupins, beets, corn, and various beans
VIIIa The Chilean Center: Chile—Potato, oilseed, grasses, and strawberries
VIIIb The Brazilian-Paraguayan Center: Brazil and Paraguay—Manioc, peanut, cocoa, rubber
plant, and maté
Conservation of Crop Genetic Resources • 421
Discussion of the geographical distribution of diversity almost always focuses on the spatial distribution of species, but biodiversity shows patterns of distribution at all levels. If we consider
genetic diversity, we might assume that infra-speciﬁc genetic diversity is evenly spread throughout
the range of the species—but this is often not the case. Studies of wild lentils (Ferguson et al. 1998),
for example, have clearly shown that the genetic diversity is not distributed evenly across its geographic range, but is concentrated in a relatively small region. Therefore, if we wish to conserve a
gene pool, we must understand the distribution of genetic diversity in relation to species ecogeographic range. The general picture that is emerging for crop plants is also supported by studies of
within- and between-population genetic variation in wild plant species.
In order to develop practical techniques to achieve conservation and sustainable use objectives,
conservation managers must use their knowledge of genetics, ecology, geography, taxonomy, and
many other disciplines to understand and manage the biodiversity they wish to conserve. Conservation and sustainable use is not just about individual plant species. Even if the conservation target
is a population of a species, no population can survive in isolation; it exists within a community or
ecosystem, interacting with other species and the abiotic environment. Examples of such interactions include pollinators, seed dispersers, microbial symbionts, herbivores (whether natural or
introduced by humans), and pathogens. Thus, when applying genetic in situ conservation for a
socio-economically important plant species, the maintenance of whole ecosystems is crucial. Plant
genetic resource conservation acts as an essential link between the genetic diversity of a plant and
its utilization or exploitation by humans (Figure 21.3).
Plant genetic diversity
The ultimate goal of genetic resources conservation is to ensure that the maximum possible genetic
diversity of a taxon is maintained and available for utilization, and as such diversity tends to focus
on speciﬁc target taxa. Faced with limited ﬁnancial, temporal, and technical resources and the
impossibility of actively conserving or monitoring all species, it is important to make the most efﬁcient and effective selection of species to focus conservation efforts.
Selection of target taxa
This choice should be objective, based on logical, scientiﬁc, and economic principles. The factors
that provide a species with “value” include:
Current conservation status
Potential economic use
Threat of genetic erosion
National or conservation agency
Biologically important species
Culturally important species
Relative cost of conservation
Ethical and aesthetic considerations
It is rare for any one factor alone to lead to a taxon being given conservation priority. More commonly, all or a range of these factors will be assessed for a particular taxon, and then it will be
assigned a certain level of national, regional, or world conservation priority. If the overall score
passes a threshold level or is higher than competing taxa, then proposals will be made to conserve
it, either in situ in a genetic reserve or on farm, or collected for ex situ conservation.
422 • The Cultural History of Plants
Plant Genetic Diversity
Selection of Target Taxa
Ecogeographic Survey/Preliminary Survey Mission
(Location, sampling, transfer, & management) (Location, designation, management, & monitoring)
Seed in vitro DNA Pollen Field Botanical
Storage Storage Storage Storage Gene bank Garden Gardens
(Seed, live, & dried plants, in vitro explants, DNA, pollen, data)
Conserved Product Deposition & Dissemination
(Gene banks, reserves, botanical gardens, conservation laboratories, on-farm systems)
Plant Genetic Resource Utilization
(New varieties, new crops, pharmaceutical uses, pure and
applied research, on-farm diversity, aesthetic pleasure, etc.)
Figure 21.3. A Model of Plant Genetic Conservation (Maxted, Ford-Lloyd, and Hawkes 1997).
Conservation of Crop Genetic Resources • 423
Once a taxon is selected for conservation, a commission statement necessarily precedes the actual
conservation activities. It establishes the objectives of the conservation proposal, and speciﬁes the
target taxa and target areas, how the material is to be utilized, and where the conserved material is
to be duplicated. It will also give an indication of which conservation techniques are to be
employed. The commission may vary in taxonomic and geographic coverage, such as onion
(Allium) species of Central Asia, Cymbidium orchids worldwide, or chickpeas (Cicer) from the
Western Tien Shen. In each case, however, a particular group of taxa from a deﬁned geographical
area must be considered currently insufﬁciently conserved (either in situ or ex situ), of sufﬁcient
actual or potential use, and/or endangered, to warrant active conservation.
Ecogeographic survey and preliminary survey mission
Once the target taxon or group of taxa is chosen, fundamental biological data is used to formulate
the most appropriate conservation strategy. The process of collating and analyzing geographical,
ecological, taxonomic, and genetic data for use in designing conservation strategies is referred to as
ecogeography (Maxted, van Slageren, and J. Rihan 1995). Ecogeographic studies involve the use of
large and complex data sets obtained from the literature and from the compilation of passport data
associated with herbarium specimens and germplasm accessions. The synthesis of these data
enables the conservationist to clearly identify the geographical regions and ecological niches that
the taxon inhabits; therefore, not only can areas with high numbers of target taxa be identiﬁed, but
also areas that contain high taxonomic or genotypic diversity, uniqueness of habitat, and economic
or breeding importance.
If the available ecogeographic data for the target taxon are limited, there will not be sufﬁcient
background biological evidence to formulate an effective conservation strategy. In this case, it
would be necessary to undertake an initial survey mission to gather the novel ecogeographic data
required on which to base the conservation strategy. The survey mission may be in the form of
“coarse grid sampling”, which involves traveling throughout a likely target region and sampling sites
at relatively wide intervals over the whole region. The precise size of the interval between sites
depends on the level of environmental diversity across the region, but it may involve sampling every
1 to 50 km. (Hawkes, Maxted, and Ford-Lloyd 2000).
The products of the ecogeographic survey or survey mission provide a basis to formulate future
conservation priorities and strategies for the target taxon. Within the target area, zones of particular
interest may be identiﬁed—for instance, areas with high concentrations of diverse taxa, very low or
very high rainfall, high frequency of saline soils, or extremes of altitude or exposure. In general, it
can be assumed that areas with very distinctive ecogeographic characteristics are likely to contain
plants with associated distinct genes or genotypes. If a taxon is found throughout a particular
region, then the conservation manager can use the ecogeographic data to positively select a series of
diverse habitats to designate as reserves. If a taxon has been found at one location, but not at
another with similar ecogeographic conditions, then these similar locations should be searched.
The ecogeographic information provides the general locality of the plant populations, but will
rarely be sufﬁcient to precisely locate actual populations. Therefore, the preparatory element of
conservation activities will be followed by ﬁeld exploration, during which actual populations are
424 • The Cultural History of Plants
located. Ideally, populations of the target taxon that contain the maximum amount of genetic
diversity in the minimum number of populations will be identiﬁed. Commonly, there is too much
diversity both in wild and domesticated species to conserve all their alleles; therefore, we must
attempt to conserve the range of diversity that best reﬂects the total genetic diversity of the species.
To identify how many population samples are required, the conservationist should ideally know the
amount of genetic variation within and between populations, local population structure, breeding
system, taxonomy, and ecogeographic requirements of the target taxon, as well as many other biological details. Some of this information will be supplied following the ecogeographic survey, but
some will remain unavailable. Therefore, the practice of ﬁeld exploration will be modiﬁed depending on the biological information on the target taxon and target area that is available.
Conservation strategies and techniques
There are two basic conservation strategies, ex situ and in situ, each composed of a range of techniques. There is an obvious fundamental difference between these two strategies: ex situ conservation involves the location, sampling, transfer, and storage of target taxa from the target area,
whereas in situ conservation involves the location, designation, management, and monitoring of
target taxa where they are currently encountered. The two basic conservation strategies may be further subdivided into several speciﬁc applications of the strategies or techniques (see Table 21.4). It
is now generally agreed that a mix of both strategies incorporating in situ and ex situ techniques,
possibly also incorporating an element of ecosystem restoration, provides the best practical
approach to integrated conservation of a particular species (Falk and Holsinger 1991).
In situ conservation involves the maintenance of genetic variation at the location where it is
encountered, either in traditional farming systems or in the wild. In situ conservation of wild
plants, such as the wild relatives of crop plants, is covered in the section on genetic reserves in the
chapter on conservation of wild plants. The process of domestication (the selection and adaptation
of wild plants for use by humans) has taken place over thousands of years, and has led to the existence of an enormous number of different landraces. Each season the farmer keeps a proportion of
harvested seed for resowing, and seed may be exchanged locally between villages. Thus, the landrace is highly adapted to the local environment, and is likely to contain locally-adapted alleles that
Botanist David Spooner (right) and Alberto Salas, plant genetic resources specialist with the International
Potato Center, Lima, Peru, collect potato germplasm in Peru for deposition in national and international
gene banks. Photo by Alejandro Balaguer. ARS/USDA.