Biodiversity
Copyright National Academy of Sciences. All rights reserved.
CHAPTER 28
IDENTIFYING AND PROTECTING THE
ORIGINS OF OUR FOOD PLANTS
J.TREVOR WILLIAMS
Director, International Board for Plant Genetic Resources, c/o Food and Agriculture
Organization, Rome, Italy
Plants that are used for food present special problems in the monitoring of genetic
diversity and its conservation. The diversity of food plants in existence today evolved over
the past 10,000 years or so since the origins of agriculture in the Neolithic era. The
progenitors of cultivated plants were wild species, which along with countless others were
harvested by hunters and gatherers. The genetic diversity of crops increased greatly as the
wild species were domesticated and were moved from environment to environment;
cultivars adapted to specific environments and were put to different uses. Many cultivars
must have been discarded even in early days, but some of them remained in certain areas
and others diversified further as they were taken far from their original homes. Hence, the
evolution of major crops has been a continuing process—from the wild progenitors to the
products of modern plant breeding and genetic manipulation.
By contrast, other species have been used as food but have never been domesticated.
Included among these are a multitude of minor fruit and forage plants that are grown in
gardens. Included too are many other species that conservationists stress for their potential
value in medicine, as food, or for other purposes. The intraspecific variability of such
species may be rather insignificant compared with that of major cultigens and is often
poorly documented. There has been less opportunity for diversification over millenia of
cultivation.
There are thus three types of wild species of interest for conservation: the progenitors
of cultivated plants; species used but not domesticated; and those that might be of use in
the future. The distinction between these categories has been
IDENTIFYING AND PROTECTING THE ORIGINS OF OUR FOOD PLANTS 240
Biodiversity
Copyright National Academy of Sciences. All rights reserved.
inadequately considered both by conservationists and by international funding
organizations in budgeting. It has led to the misuse of the term “genetic resources” as a
justification for almost any conservation activity, and may also lead to confusion and to
the unscientific planning and operation of programs. A significant exception remains the
work on crop plants guided by the International Board for Plant Genetic Resources
(Williams, 1984).
THE INTERNATIONAL BOARD FOR PLANT GENETIC
RESOURCES PROGRAM
The International Board for Plant Genetic Resources (IBPGR) was established within
the Food and Agriculture Organization because of the loss of substantial intraspecific
diversity produced by domestication as fewer and fewer successful modern cultivars were
grown over large areas of land. This loss was termed genetic erosion.
When IBPGR was created in 1974, the mandate given to it by the Consultative Group
on International Agricultural Research (CGIAR) was to establish a global network of
activities to further the collection, conservation, documentation, and use of germplasm for
crop species. The network, which has been in existence for some time, is complex and
includes gene banks (repositories of seeds, tubers, and other sources of genetic materials)
at conservation centers and activities dealing with the collection, characterization and
documentation of crop genetic resources, and training. Beginning with a handful of
countries in 1974, IBPGR'S work now involves 106 countries, and the number of gene
banks has grown from half a dozen in 1974 to more than 100, about 40 of which have
agreed to accept responsibility for long-term maintenance of genetic resources. The more
than 50 crops in the IBPGR program include cereals, legumes, vegetables, oil seeds,
fruits, and a limited number of cash crops of importance to rural farmers. More recently,
forage plants have been included.
Emphasis was initially placed on the collection and conservation of local cultivars of
crops that had evolved in diverse environments under traditional agricultural practices;
these are often known as landraces. Farming methods were also changing rapidly due to
the availability of modern cultivars and agricultural techniques. The landraces have
provided and continue to provide a rich resource for exploitation, but it is neither
practicable to collect and conserve all of them nor is it necessary. Attempts have mainly
been directed to securing representative samples from those areas with the richest
diversity. These genetic resources have always been regarded by the IBPGR as a heritage
of mankind to be freely available to all bona fide users.
Much of the diversity of crop plants of use in plant breeding is of cryptic expression.
There are clearly limited numbers of morphological characteristics of the plant, and many
of them, with the exception of those controlling such yield determinants as the number and
size of ears of corn, may be agronomically irrelevant. Physiological characteristics
abound, however, controlling life cycle through photoperiodicity, breeding system, and
numerous responses to stress factors such as salinity, drought, and especially pests and
diseases. Conserved samples are used primarily as a source of genes for broadening the
genetic base of modern cultivars
IDENTIFYING AND PROTECTING THE ORIGINS OF OUR FOOD PLANTS 241
Biodiversity
Copyright National Academy of Sciences. All rights reserved.
and thereby counteracting the vulnerability of cultivars with too narrow a genetic base to
resist new races of pests and diseases.
IBPGR's emphasis began to shift away from the collection of landraces as its work
progressed and as plant breeding techniques advanced, and to include the wider gene pools
of the crops such as the wild progenitors and close relatives. The materials conserved
embrace an evolutionary spectrum of the past 10,000 years and include obsolete and fairly
recent cultivars, but breeders' lines rarely need conservation; their diversity is already
present elsewhere. This point, which is not widely understood, has led pressure groups to
urge the conservation of breeders' lines, which except in a few cases is not justified. In any
case, germplasm for major staple crops is available from the International Centres of the
CGIAR, the parent body of IBPGR, and from several national agricultural research
organizations.
For most of the major crops, germplasm collections provide opportunities for
continued introduction of genes with conventional or sophisticated breeding techniques.
For many minor crops that have not greatly diversified following domestication,
collections may contain cultivars that may be introduced as crops to other countries
without further breeding. Hence, the collections of the major crops, e.g., rice, wheat,
millet, and groundnut, will be large, whereas those of the minor ones, e.g., okra, many
tropical fruits, and forage crops, will be relatively small. As the value of such minor crops
becomes appreciated, however, there is likely to be a need for a more diverse germplasm
base.
The IBPGR budget is small (a little over U.S. $5 million per year); hence, it does not
provide long-term institutional or program maintenance support but, rather, serves as a
stimulus or catalyst to work done by national or international organizations. Some of its
funds are used to carry out urgent work and to fill gaps in the collection. Linked with the
IBPGR program are all crop genetic resources activities in the world, many collections of
which were initiated and supported by IBPGR. IBPGR coordinates rather than directs
these activities in which all participants are equal partners.
To date, IBPGR has organized more than 500 collecting missions in scores of
countries. Germplasm has been acquired in accordance with established priorities
(IBPGR, 1981; Williams, 1982) and conserved in long-term storage in 40 centers around
the world. All major crops have now been placed in designated gene banks. The IBPGR is
currently reviewing the financial support it gives to such gene banks and to centers that are
actively involved in ensuring that genetic resources are available for use in crop
improvement programs.
CROP ORIGINS AND GERMPLASM USE
Over the past few decades, a great deal of information has been accumulated on the
origin and evolution of cultivated species. In general, the wild species tend to have limited
patterns of distribution. Although Vavilov (1951) laid the basis for further work in
defining centers of origin and centers of diversity based on observed botanical variation,
the nuclear centers of the origin of agriculture have
IDENTIFYING AND PROTECTING THE ORIGINS OF OUR FOOD PLANTS 242
Biodiversity
Copyright National Academy of Sciences. All rights reserved.
been confused with the areas of evolution and diversity of crop plants (Hawkes, 1983).
Harlan (1951) identified smaller microcenters that are rich in diversity and not necessarily
near civilization nor confined to plains or mountains—features strongly associated with
the Vavilovian centers—usually in the areas that would be regarded as broader centers of
diversity.
There are therefore different definitions of the regions that comprise centers—from
Vavilov's to those of Zhukovsky (1975). Whatever the definitions, it is still clear that there
are areas where crop plant diversity is great and others where it is slight. The centers of
diversity of several crops coincide and comprise limited numbers of regions in contrast to
the 13 centers proposed by Vavilov. Crop germplasm is by no means obtained solely from
developing countries; centers also cover areas of the developed world. Examples of crops
that originated in the developed world include the adzuki bean (Vigna angularis) in Japan,
oats (Avena sativa) and rye (Secale cereale) in northern Europe, and the sunflower
(Helianthus annuus) in the United States. Many old landraces of the developed world are
extremely valuable resources being fed back, through breeding, to Third-World
agriculture.
In view of the apparent confusion surrounding the definition of the regions of
diversity, it is pertinent to question how the material can best be identified and preserved.
Over the past decade IBPGR's strategy has been to mobilize scientific information from
hundreds of the world's best breeders and crop botanists. Scientists who have grown, used,
and evaluated germplasm know far more about its variability than collectors who can only
observe phenotypes. This strategy has been highly successful in ensuring the preservation
of intraspecific diversity in a very limited time and is still implemented.
For the wider gene pools, where species and species relationships are the principal
interest, taxonomy plays a major role in the conservation of genetic resources work,
especially experimental taxonomy designed among other things to clarify genomic
relationships. But information on the origins and evolution of crop gene pools is obtained
not only from taxonomy but also from a synthesis of disciplines, including archaeology,
linguistics, ecology, and molecular biology.
For some of the major crops, e.g., wheat and maize, there are still gaps in our
knowledge, but in many other cases, the progenitors are well known. Although the
ancestor of the faba bean (Vicia faba) has not been equivocally identified, several closely
related species have frequently been found, the most recent during an IBPGR mission to
Syria in 1986. Truly wild forms of cassava are not definitely known either, although
Brazilian workers supported by IBPGR may have found one in 1986.
When a theory of origin has been postulated but not verified by taxonomic work, it
may not be clear what germplasm should be collected and where. The cowpea (Vigna
unguiculata) is a good example; taxonomically its ancestral home has been variously
proposed as Ethiopia or central/southern Africa. IBPGR examined all herbarium
specimens of this species in 1986 and found that the progenitor of the cowpea occurs in
every country of sub-Saharan Africa. Thus until experimental work on freshly collected
material is complete, we will not know the patterns of variation or where to collect
samples. Meanwhile, collection of material
IDENTIFYING AND PROTECTING THE ORIGINS OF OUR FOOD PLANTS 243
Biodiversity
Copyright National Academy of Sciences. All rights reserved.
will be ad hoc and provide useful allelic diversity but not necessarily from the ancestral
area of domestication.
In other cases, such as that of citrus crops (Citrus spp.), existing classifications are
substantially untested in the field. IBPGR has put emphasis on relatives of the lime,
lemon, and orange and will be organizing fieldwork to this end—not knowing whether the
taxonomy works or not. Obviously, the field strategy may have to be modified to fit new
knowledge and adapted as necessary. The collection and conservation work will no doubt
greatly add to information on the origins, evolution, and distribution of Citrus gene pools.
This has already proved true for beans of the genus Phaseolus (G.Debouck, IBPGRI/
Centro Internacional de Agricultura Tropical, Colombia, personal communication, 1986),
coles (Brassica) (wild gene pool of the Mediterranean), perennial soya bean (Glycine)
(IBPGR collaborative work in Australia; A.H.D.Brown, Commonwealth Scientific and
Industrial Research Organization, Australia, personal communication, 1986), African
eggplants (Solanum spp.) (Lester et al., 1986), and cucurbits (Cucurbitaceae) (L.Merrick,
University of California, Davis, personal communication, 1986). Numerous other crops
will be worked on in a similar way.
Harlan and de Wet (1971) defined primary, secondary, and tertiary gene pools on the
basis of the degree to which closely and distantly related species can be cross-bred.
Hitherto a gene-pool approach has been taken in defining IBPGR work. This has obviously
been the best strategy, because wild progenitors and their related species have increasingly
been shown to be valuable sources of genes for crop improvement. Others, such as wheat,
are used for transferring entire chromosomes or parts of chromosomes. Both somatic
hybridization and conventional crossing are likely to be more successful among closely
related species, but embryo rescue techniques are already commonly used where the
parents are less closely related, e.g., in wide crosses between wheat or barley and related
wild grasses.
Many advances will continue to come from breeding closely related plant species,
but where breeding is far advanced, even species of the tertiary gene pool are useful.
IBPGR has recognized this for two groups: first, wild grasses of the tribe Triticeae, which
includes wheat, barley, rye, forages, and dozens of species in more than 20 genera
distributed throughout the world, and second, the East Asian-Pacific-Australian species of
soya bean of the tertiary gene pool. In other cases, the wider gene pool has been used very
little; hence, conservation priorities have been imprecisely defined. Wild plants related to
maize in the genus Tripasacum are unlikely to be used in maize breeding before the next
century.
EVALUATION OF THE RESOURCES
Integral to crop genetic conservation, but a step subsequent to collection, is
description and evaluation of germplasm. Although this activity lags behind, it is an
ongoing, long-term process. In autumn 1985, IBPGR held a small strategy workshop to
look at the collections and study how they could be used more effectively. It has initiated,
in particular, research and development to see how best to work on subsets of large
collections, thereby accelerating work. Physiological or otherwise cryptic variation must
be thoroughly assessed during this process.
IDENTIFYING AND PROTECTING THE ORIGINS OF OUR FOOD PLANTS 244
Biodiversity
Copyright National Academy of Sciences. All rights reserved.
By contrast, other conservation programs lack this user-driven input. It seems to me
that scientists must develop aesthetic, moral, and evolutionary arguments for wider
conservation practices that are not based on whims of individuals but, rather, are geared to
perceived needs such as environmental stabilization and rational land-use planning. Only
when studies on biological diversity provide data for these arguments can a clear rationale
be presented. It is evident that the environmental data bases needed by my community of
scientists are only just being developed. Interestingly, when speaking about wild relatives
of crops, a well-known crop botanist recently said that identification of environments was
more important than proceeding from past taxonomy and searching large areas with often
poor chances of success (G.Ladizinsky, Hebrew University of Jerusalem, Israel, personal
communication, 1986).
SCIENTIFIC SUPPORT FOR GENETIC RESOURCES WORK
Conservationists outside the field of crop genetic resources frequently base their plea
for conservation of wild species on spurious evidence and unrecognized needs resulting
from a lack of adequately trained scientific manpower. The work in crop genetic resources
has been successful because of its user orientation, and in fact has been solely directed to
this end. There is a clear lesson here for the wider conservation movement and also a
reminder of the need to identify gaps in scientific knowledge.
The success of IBPGR would not have been possible without the work of botanists,
geneticists, and scientists in related disciplines. Nonetheless, there has been insufficient
scientific research pertinent to the conservation of crop genetic resources. This has been
partly due to lack of funding and partly to the fact that strategic research is often not as
attractive to the academic community as basic research. Accordingly, IBPGR has had to
shift its program to accommodate strategic problem-solving research, much of it of an
interdisciplinary nature.
Areas of research where such problems exist are:
• the elucidation of patterns of genetic variation using such disciplines as
taxonomy, ecology, cytogenetics, molecular biology, and population genetics;
and
• the understanding of genetic stability in conservation systems, again as
interdisciplinary work involving genetics, tissue culture, molecular biology, and
seed physiology.
IBPGR has initiated relevant research that not only will provide practical solutions to
specific problems but also will add to scientific knowledge. Traditional disciplines such as
taxonomy and cytogenetics have to keep up with exciting new developments in, for
instance, molecular biology. One recent development is the proposal that DNA is in a state
of flux. Exchange of genetic material between organelles and nuclei may be possible,
while bacterial infection and tissue culture, for instance, may induce new genomic changes
in response to changed environments (Hohn and Dennis, 1985).
IDENTIFYING AND PROTECTING THE ORIGINS OF OUR FOOD PLANTS 245
Biodiversity
Copyright National Academy of Sciences. All rights reserved.
On the whole, conservation biologists have not fully considered the technologies
necessary for scientific and practicable solutions and need a synthesis of data from
numerous disciplines. One recent initiative, that is supported in part by the government of
the United Kingdom and draws on a wide range of expertise, is the International Legume
Database Information Service (ILDIS). IBPGR has been associated with this service from
its inception and views positively the mobilization of scientists within several institutions.
Yet the provision of checklists of taxa continent by continent draws heavily on traditional
taxonomy. This venture and the Missouri TROPICOS system and the BIOSIS
(BioSciences Information Service) Taxonomic Reference File are to be applauded.
EX SITU AND IN SITU PRESERVATION
Because of their nature, most crop genetic resources are conserved ex situ. Many crop
relatives are annuals or weeds associated with disturbed agricultural environments, and
most do not lend themselves to in situ conservation. Landraces cannot be conserved by
growing them in primitive agricultural conditions; it is neither practical nor can it be
justified morally. There are exceptions to what can be conserved in situ, especially
perennial species associated with complex ecosystems such as tropical rain forests, e.g.,
cocoa, oil palm, relatives of Citrus, and some root crops. To encourage in situ conservation
where it is relevant and to rationalize further collecting work, IBPGR has recently been
developing its expertise in the ecogeographic sampling and monitoring of genetic
resources. But the opportunities for in situ conservation are limited and should not be
overemphasized.
In addition, preservation of species diversity by ecosystem maintenance is not always
relevant to the conservation of crop genetic resources. Allelic diversity is rarely considered
by ecosystem conservationists, yet it is needed for utilization by crop botanists (Frankel
and Soulé, 1981; Ingram and Williams, 1984).
The interface between ecosystem conservation and the special needs to conserve crop
genetic resources has been discussed by Ingram and Williams (1984). Many of the
scientific points have not yet been addressed by the wider conservation movement and
merit further attention if scientific objectivity is to prevail over emotive generalization.
REFERENCES
Frankel, O.H., and M.E.Soulé. 1981. Conservation and Evolution. Cambridge University Press,
Cambridge. 327 pp.
Harlan, J.R. 1951. Anatomy of gene centers. Am. Nat. 85:97–103.
Harlan, J.R., and J.M.J.de Wet. 1971. Towards a rational classification of cultivated plants. Taxon
20:509–517.
Hawkes, J.G. 1983. The Diversity of Crop Plants. Harvard University Press, Cambridge, Mass. 184
pp.
Hohn, B., and E.S.Dennis, eds. 1985. Genetic Flux in Plants. Springer-Verlag, New York. 253 pp.
IBPGR (International Board for Plant Genetic Resources). 1981. Revised Priorities Among Crops and
Regions. IBPGR Secretariat, Rome. 18 pp.
IDENTIFYING AND PROTECTING THE ORIGINS OF OUR FOOD PLANTS 246
Biodiversity
Copyright National Academy of Sciences. All rights reserved.
Ingram, G.B., and J.T.Williams. 1984. In situ conservation of wild relatives of crops. Pp. 163–179 in
J.H.W.Holden and J.T.Williams, eds. Crop Genetic Resources: Conservation and
Evaluation. Allen and Unwin, London.
Lester, R.N., J.J.G.Hakiza, N.Stavropoulos, and M.M.Teixiera. 1986. Variation patterns in the African
scarlet eggplant. Pp. 283–308 in B.T.Sytles, ed. Infraspecific Classification of Wild and
Cultivated Plants. Clarendon Press, Oxford.
Vavilov, N.I. 1951. The origin, variation, immunity and breeding of cultivated plants. Chronica Bot.
Volume 13. 364 pp.
Williams, J.T. 1982. International programs with special reference to genetic conservation and the
role of the United States. Pp. 52–55 in Proceedings of the U.S. Strategy Conference on
Biological Diversity 1981. Publication No. 9262. U.S. Department of State, Washington,
D.C.
Williams, J.T. 1984. A decade of crop genetic resources research. Pp. 1–17 in J.H.W.Holden and
J.T.Williams, eds. Crop Genetic Resources: Conservation and Evaluation. Allen and Unwin,
London.
Zhukovsky, P.M. 1975. Mega-genecenters and Endemic Micro-genecenters: World Gene Pool of
Plants for Breeding. USSR Academy of Sciences, Leningrad. 116 pp.
IDENTIFYING AND PROTECTING THE ORIGINS OF OUR FOOD PLANTS 247