The conservation of crop genetic resources primarily focuses upon three types of crop germplasm: (1) wild crop varieties (2) semi-domesticated, weedy crop relatives, and (3) landraces of ancestral crop species. These categories are given priority because they are considered most at risk, they exhibit great intra and interspecific diversity, and/or they are most useful for agricultural production.

Wild and Weedy Crop Relatives: Both exist in natural ecosystems, often in the perimeters of agricultural fields or fallowed areas. In countries where farmland is expanding, the habitats for these wild and weedy crop varieties are threatened. Herbicide use can also endanger their existence (Brush, 1991). Many of these wild and weedy varieties have disease and pest resistances which have been used in the development of modern crop varieties.

Landraces of Ancestral Crop Species: These crop resources are endemic to the cradle areas of crop domestication and evolved in association with traditional, low input farming systems that used minimal levels of fertilizer, cultivation and chemical plant protection. Because landraces originated and continue to be grown in marginal farming areas, they demonstrate characteristics such as hardiness and dependability rather than high productivity (Frankel et al., 1995). Farmers have traditionally maintained them as a means of insuring stability and also because landraces often have a unique food use, provide good animal feed, meet additional household needs, or have religious, ceremonial and cultural significance. Having evolved in stress-prone environments, many landraces can withstand extreme temperatures, high water stress, and/or disease and pest resistancy. The conservation of crop genetic resources relies upon in situ and ex situ conservation strategies. Ex situ (or off site) conservation takes the form of a gene bank where seeds and tissue cultures of rare and endangered plants are preserved. These gene banks often hold thousands of accessions (samples) of plant species. Despite the fact that the accessions predominately originate in the countries of the South, gene banks are most common and most extensive in the countries of the North. Gene banks are primarily run by NGO's or government agencies and typically provide free samples to research institutions and private industry. Both ex situ and in situ conservation have strengths and weaknesses and the effectiveness of one strategy over the other only becomes clear when evaluated on a case by case basis. However, there are some general concerns about the applicability of each method that can be addressed. The advantages of ex situ conservation include: the ability to warehouse thousands of plant accessions in a small space, research is easier with such collections, species are secure even if their original habitats are lost, in some cases it may be more economical than on-farm conservation, and there is already an extensive body of research on the technology and management of gene banks. Disadvantages often attributed to gene banks and ex situ conservation are that such warehouses cannot realistically hold all of the existing genetic diversity and when stored, the genetic integrity of these resources can be compromised through natural hybridization and genetic drift. Additionally, the natural evolutionary breeding processes, which occur continuously on the farm and are critical for the generation of new genetic diversity, are halted in the gene banks. While in situ (or on farm) conservation has historically been the main method used by farmers for conserving crop genetic diversity, it has only recently attracted attention by NGO's and research institutions. With the increasing recognition that ex situ holds many limitations, in situ has gained wider support. Supporters of in situ methods cite the importance of conserving the farmers' traditional knowledge and the importance of maintaining the natural agroecosystem which provides an environment where new genetic diversity arises from the crossing of wild crop relatives with landraces and modern varieties. Traditional seed management practices are often viewed as the most reliable genetic resource conservation strategy. For many small-scale farmers, crop genetic diversity has been their greatest resource and they have become experts in using it to sustain their yields and avoid crop failure. On the other hand, in situ conservation is often seen as impractical or even impossible in many regions, particularly in drought-prone farming systems. And in many of these centers of crop genetic diversity, there is political turmoil which prevents the secure existence of these "living gene banks". Moreover, as traditional agricultural systems become more integrated into the market economy, cash crops and commercial inputs may make local crop varieties and landraces less useful to farmers (Bellon, 1996).

The discipline of economics addresses environmental problems by examining the intrinsic and explicit values of natural resources. Economists do so by first demonstrating the economic or social value of a resource. Secondly, they try to explain why despite the value it continues to be threatened. Lastly they try to find ways to realize this value by internalizing the social values and costs to create incentives for conservation of the resource. This short discussion of the economic value of crop genetic resources follows this same format.

From 1930 - 1975 over half the global yield increase in cereal crops, sugar cane, cotton and groundnut is attributed to the contribution of genetic resources. In animal sciences genetic resources are estimated to have increased milk yield 25% during the same period. The USDA estimates that 1% of the US annual increase in production is due to genetic resources. Assessments of the transfers of benefits to Northern countries using the genetic resources of Southern countries vary. One calcu-lation from CIMMYT (International Maize Center) estimates for wheat and maize alone that the annual benefits for Australia amount to $75 million, the United States $500 million and 2.7 billion per year for all OECD countries.

The green revolution produced fantastic results by increasing agricultural yields through the introducing of new plant breeds with shorter stocks to allow for less wind damage and more kernel production. Where conditions were favorable, up to three crops per year were possible where previously only one had been grown. From 1961 - 1980 developing countries’ cereal yields rose by 2% annually with wheat rising by 2.7% and rice by 1.6%; in countries with ample irrigation it increased up to 3% (Dictionary of Environment and Development 1993).

However, new seeds required high inputs and favorable conditions: irrigation, good soil and mechanization. Thus biodiversity tends to be concentrated where the green revolution had little impact. These areas are the storehouses of much of the world’s remaining crop genetic diversity. By 1980 27% of all seeds used in developing countries were high yielding varieties (HYV). However, between developing countries there is a dramatic regional imbalance: 9% of all seeds in Africa are HYV as compared to 44% in Latin America. The genetic diversity which remains tends to be concentrated in some of the world’s poorest regions and countries.

Why crop diversity continues to be threatened:

Crop diversity is threatened for many of the same reasons as biological diversity: habitat loss, increased globalization, human induced species selection and increased market integration. However, crop genetic diversity differs from general biodiversity in that many of the species require human care and cultivation. The economics of the resource is also different since they are generally regarded as an input into the production process of agriculture. Therefore much of the value of crop diversity has immediate monetary benefits to society.

Where crop and biological diversity do overlap is in sharing the same market failure of information uncertainty regarding the use of the resource. It is impossible to determine which characteristics a plant breeder of the future may find useful. New crops are continuously bred for changing climatic, agronomic and market conditions.

The value of this resource to individual farmers, however, is often less than that to society. Socially plant genetic resources have high option values. That is, we are willing to pay to keep the option of using the resource at some unspecified time in the future. Yet to individual farmers who may be currently preserving the genetic stock, there may be a high cost in continuing to grow a traditional variety if a HYV can be grown. While there are many reasons why farmers might continue to cultivate traditional varieties, the most genetically diverse farms tend to be distributed in marginal areas of cultivation.

Creating incentives:

Many authors stress that to preserve the resource we must use it (Fowler and Mooney 1990, World Wildlife Fund 1986). Genetic resources are unique in that they are a none rival good. That is, the use of a genetic resource by one person does not exclude its use by another. This remains the case as long as genetic resources continue to be regarded as a "common heritage". While keeping the resource an open access good may prevent some of the abuses of international patent laws by seed companies, it also prevents local farmers and breeders from reaping the benefits of their work. Policies and programs to increase in-situ preservation include increasing their market value for use in specialty markets which cater to local tastes or elite consumers.

Problems with economic incentives:

There is a final caveat regarding the reliance on market mechanisms to preserve crop biodiversity. In creating market based incentives there may be good and potentially insurmountable reasons why they don’t already naturally exist. Aspects of the resource such as the lack of information, an inability to determine the origin of genetic material and its public good nature may serve to prevent any sort of market incentive from working.

While economic incentives may work for domesticates, they will probably not preserve wild species which interact with on-farm crops. This is a tricky subset of biological diversity which sits somewhere between biodiversity and crop genetic resources.

Finally, economic incentives usually only work when policy makers are able to target the market imperfection directly. Incentives require a narrow and specific target. Exactly how much biodiversity we need is still an undefined concept. Without specific targets incentive programs may be either be short-term or produce perverse outcomes.

Aside from the explicitly economic concerns that come to bear when discussing preservation of crop genetic resources, there are numerous political and sociological issues involved as well, whether we are discussing in situ or ex situ conservation of genetic diversity.

In most countries, scientific or government institutions have set up seed banks or other forms of stockpiling a variety of crop germplasm (the plant part useful in crop breeding because it contains the genetic attributes), but unless the seeds are grown out and bred to new seed, they might die. In addition, this ex situ form of preservation does not allow for continuing evolution of crop plants in their native habitats and/or through indigenous or traditional farmer selection methods.

So although ex situ conservation is important (to at least keep a snapshot-in-time of the varieties we have now), the preservation of in situ crop diversity is equally, if not more, vital. When we speak of in situ genetic preservation, we are acknowledging that a great deal of crop diversity remains in the home gardens and on the village margins of what we call the "cradles of domestication" of the world’s primary food crops, geographic regions that tend to lie in Third World, mostly tropical areas. Any First World involvement in preserving the remaining genetic diversity in these areas will, of necessity, involve dealing with a variety of peoples and governments, at many scales, from local to national to international.

The key players vary far and wide. They include indigenous peoples, Third World farming households and villages, regional and national government extension programs, international governmental and non-governmental organizations, for-profit seed companies, and research scientists from around the world. Each player has a different point of view and a different goal. While individual farmers may be most interested in growing enough food, of enough variety, to survive and/or to keep up with cultural obligations, multinational corporations may be most interested in finding a variety with some desired characteristic, then patenting that plant’s genome.

The Green Revolution of the past involved bringing in high-yielding improved crop varieties that tended to require high levels of chemical inputs (fertilizers and pesticides), and its success rate varied with region and country and with the goals of the person planting the seed. In the past few decades, we have found that the improved varieties don’t meet all the needs of all the farmers in the Third World. Some farmers grow a crop with more than high yield in mind, especially if they live too far from a population center in which they could market the excess crop. Sometimes, local tastes demand several varieties of, for example, corn in Central America. Likewise, local peoples may use a certain crop for more than meeting food needs, and in that case the improved variety may not meet their needs for, e.g., fiber or animal fodder.

The issue of genetic engineering and agriculture is also a thorny one, socio-politically. Although lab-based methods of changing the genetic makeup of crop varieties are usually accomplished more quickly than the field-based methods of cross-breeding, it is, in some ways, terra incognito: now that humans can put animal genes into plants, which could never happen in the field, the long-term results are unpredictable. Introducing alien genetic material into a crop line could potentially result in a host of threats, such as conveying unknown genes into the wild (through outcrossing of the crop with its weedy relatives) or exacerbating First World/Third World inequalities (through intellectual property rights problems, in which private corporations own the rights to, and profit from, genes that provide some desired attribute in the crop; genes that, in some cases, were selected for over many years and nurtured in situ by local, usually poor, farmers) (Borowitz 1994).

Another key point to remember with biotechnology is that scientists are just relocating existing genetic material, not creating new genes. Therefore, any future advances that we might hope to come out of genetic engineering will have to rely on the natural genetic diversity that nature, and indigenous peoples centuries of crop selection, have provided.

Thus, in situ conservation of crop diversity, and encouragement of traditional farming methods, will remain important undertakings for the long-term. According to Fowler and Mooney (1990), Agricultural diversity cannot be saved without saving the farm community. Conversely, communities must save their agricultural diversity in order to retain their own options for development and self-reliance. In the end, the need for diversity is never-ending. Therefore, our efforts to preserve this diversity can never cease. Because extinction is forever, conservation must be forever.

The case study by Esquivel and Hammer on Cuban home gardens, conucos, demonstrates many of the issues on genetic diversity and sustainable development that were discussed above. But contrary to many of the perceived benefits or disadvantages of ex situ and in situ conversation, the authors present a case study that shows how for Cuba in situ conservation has numerous advantages for the conservation of landrace varieties. Moreover by discussing the historical arrival of many of the landrace varieties found in Cuba today, the authors demonstrate the intractable role that humans play in both seed dispersal and conservation.

The conucos reflect a type of sustainable or traditional agriculture (also an example of sustainable development) that has evolved since 500 AD based mostly on Indian agriculture methods from South and Central America who migrated to Cuba. The method of plant cultivation has itself promoted genetic diversity preservation or in situ conservation.

Cuban farmers have shown that landraces, contrary to conventional research, can and do out-perform modern varieties. Therefore, there is a tendency for Cuban farmers to choose the landrace over the modern variety, not only for taste or hardiness, but also for yield. Farms in Cuba as a result are being cultivated with both traditional and MV’s to achieve greater yields and meet the local food needs of the Cuban population. Moreover, the presence of the conucos and landrace varieties in Cuban society is so strong that the government is enacting programs to strengthen both local food supplies and traditional plant varieties, primarily medicinal, that incorporate both traditional and modern varieties. Additionally, the way conucos are cultivated harnesses the natural climatic and geographical forces of the eco-system to create a healthy and highly productive synergy between plants, soil, and climate. Since the conucos feed the soil, maintaining its fertility, conucos promote the longevity and sustainability of the soil.

The history of plant diversity in Cuba (and likewise the important contribution of this article to the discussion on sustainable development) relates a process of human movement (development) as a form of seed dispersal and also a perpetuation of traditional agricultural methods. Cuban conucos are therefore not a model per se of sustainable development, although they do demonstrate sustainable human processes by relating the continuity and importance of values and historical traditions that affect how crop and plant genetic resources have been (and are) used and dispersed.

Conclusion: The above discussion illustrates many of the concepts economic, scientific and social that pertain to the survival of plant genetic diversity. Notably, humans have had an extensive influence on the evolution, survival, and domestication of crop and plant genetic resources. Much of the challenge facing people today is meeting the food demands of a projected population explosion. The central question is how to meet these demands and changes without losing crop genetic diversity. As a result of genetic engineering for large scale agriculture, seed and plant material is increasingly homo-genized. Another consequence is the loss of traditional knowledge about landrace varieties and agricultural methods. Many attempts to maintain genetic diversity are being made from ex situ and in situ conservation to economic and market incentives that promote conservation.

Bellon, M.R. 1996 The Dynamics of Crop Intraspecific Diversity: A Conceptural Framework at the Farmer Level. Economic Botany 50 (1): 26- 39.

Brush, Stephen. 1991 A Farmer-Based Approach to Conserving Crop Germplasm. Economic Botany 45: 153-165.

Borowitz, Susan. 1994. Biotechnology: potential threats concerning genetic engineering and agriculture. Terrain: The Monthly Publication of the [Berkeley, California] Ecology Center.  June 1994.

Esquivel, M. and Hammer, K. The Cuban Homegarden conuco: a perspective environment for evolution and in situ conservation of plant genetic resources,î Genetic Resources and Crop Evolution. Kluwer Academic Publishers, Netherlands. 1992.

Frankel O., Anthony H.D. and Jeremy. J.B. 1995. The Conservation of Plant Biodiversity. Cambridge: Cambridge University Press. Pp. 39-117.

Fowler, Cary and Pat Mooney. 1990. Shattering: Food, Politics and the Loss of Genetic Diversity. Tucson: University of Arizona Press.

Grump, Andy. 1993. Dictionary of Environment and Development. Earthscan Publications Limited: London.

World Wildlife Fund. 1986. The Wild Supermarket: the importance of biological diversity to food security. World Wildlife Fund: Washington D.C.

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