Thursday, June 13, 2024

The issues of in situ conservation of crop genetic resources

Domesticated plants have been fundamentally altered from their wild relatives; these species have been moved into and adapted to new environments; they have become dependent on the tiller’s hand; and they have been reshaped to meet human needs and wants. Modern crops are the result of thousands of years of these evolutionary processes. Like all biologicalnevolution, crop evolution involves two fundamental processes: the creation of diversity and selection (Harris and Hillman 1989). Crop evolution is distinguished by two types of selection: one natural and another artificial or conscious. These evolutionary processes must continue in order for agriculture, a living and evolving system, to remain viable. Therefore, an essential criterion of crop evolution is the availability of genetic diversity. Crop evolution has been altered by our enhanced ability to produce, locate, and access genetic material, but this has not changed its fundamental nature.

Both farmers and scientists have relied on the store of genetic diversity present in crop plants that has been accumulated by hundreds of generations who have observed, selected, multiplied, traded, and kept variants of crop plants. The result is a legacy of genetic resources that, today, feeds billions of humans.

Genetic diversity is important both to individual farmers and farming communities and to agriculture in general. Individual farmers value diversity within and between their crops because of heterogeneous soils and production conditions, risk factors, market demand, consumption, and uses of different products from an individual crop species (Bellon 1996). Thus a wheat farmer in Turkey may have different types of wheat for hillside or valley bottom areas, for irrigated and rain-fed parcels, for homemade bread and for urban grain markets, for straw and animal feed (Brush and Meng 1998). Moreover, farmers usually rely on diversity of other farms and communities to provide new seed when crops fail or seed is lost or to renew seed that no longer meets the farmer’s criteria for good seed (Louette et al. 1997). The need for diversity at both the farm and regional levels has resulted in a vast store of genetic diversity in crops, a store passed down from earlier generations and maintained for the future. In regions where a crop’s evolution has the longest record, where the crop was originally domesticated, and where its diversity is greatest, the local store of genetic diversity in farming communities is also a store of genetic resources for that crop, an invaluable resource for farmers, scientists, and consumers elsewhere (Hawkes 1983).

Unfortunately, this legacy is imperiled by the very conditions it helped to create (Wilkes 1995). Record numbers of humans, agricultural science and technology, and economic integration of the world’s many diverse cultures threaten to destroy this legacy, as modern crop varieties and commercial farming diffuse into every agricultural system. A result of these changes is that diversity on individual farms and across wide regions is threatened by modern crop varieties that have been bred for broad adaptation, resistance to disease and other risk factors, ability to better use water and fertilizer, and higher yields. This threat is evidenced by the fact that agricultural development in Europe, North America, and many less developed countries has been accompanied by the replacement of diverse, local populations of crops with a handful of modern varieties.

The importance of crop genetic resources and threats to them has led to the creation of conservation programs to preserve crop resources for future generations. One type of crop genetic conservation is ex situ — maintenance of genetic resources in gene banks, botanical gardens, and agricultural research stations (Plucknett et al. 1987). Another type is in situ —maintenance of genetic resources on-farm or in natural habitats (Brush 1991; Maxtel et al. 1997a). In actuality, two types of in situ conservation can be distinguished. First, in situ conservation refers to the persistence of genetic resources in their natural habitats, including areas where everyday practices of farmers maintain genetic diversity on their farms. This type is a historic phenomenon, but it is now especially visible in regions where farmers maintain local, diverse crop varieties (landraces), even though modern, broadly adapted, or higher yielding varieties are available.

Second, in situ conservation refers to specific projects and programs to support and promote the maintenance of crop diversity, sponsored by national governments, international programs, and private organizations. In situ conservation programs may draw on the existence and experience of the first type, but they are designed to influence farmers in the direction of maintaining local crops by employing techniques that may not be local. This type of conservation faces daunting tasks. It must cope with continual social, technological, and biological change while preserving the critical elements of crop evolution — genetic diversity, farmer knowledge and selection, and exchange of crop varieties.

In situ conservation practices and projects in agriculture theoretically can concern the wide spectrum of genetic resources relating to crops, from wild and weedy relatives of crop species to the infraspecific diversity within crop species (Maxted et al. 1997b). The exemplified by heterogeneous crop populations known as landraces. These are named, farmer varieties that usually have a reduced geographic range, are often diverse within particular types, and are adapted to local conditions (Brush1995; Harlan 1995). One reason for our focus on diversity within cultivated crops is that science of in situ conservation of cultivated resources is relatively less developed than the science of conserving wild resources such as wild and weedy crop relatives. Another reason is that in situ conservation of cultivated plants requires novel approaches, while in situ conservation of wild crop relatives can draw on theories and methods developed for conserving many different species in their natural habitats. Finally, focusing on variation within cultivated species is warranted by the fact that this type of diversity is arguably the most important one for the future viability of agricultural evolution, as it has been in the past.

The successful planning and implementation of projects for on-farm (in situ) conservation of crop genetic resources require us to answer four questions.

First, why undertake this type of conservation, especially when investments are made for ex situ conservation? Second, what scope is necessary or appropriate for in situ conservation of crop germplasm? Third, how can agricultural agencies and organizations promote this form of conservation? Finally, what legal and institutional questions pertain to on-farm conservation of genetic resources? The answers to these questions come from different fields of science, for example, population biology and social science, and from law and politics. Moreover, the answers to these questions seldom are definitive. More important than definitive answers is the ability to seek answers, because new answers will be needed for different times, conditions, crops, and societies.

The purpose of this and other chapters in this book is not to answer these four questions but rather to offer guideposts and a context for finding answers in specific regions and for specific crops and cropping systems.

Why in situ conservation?

The invention and development of agriculture was accomplished independently in several places in the world, but within a relatively narrow time period following the end of the Pleistocene period — 8,000 to 10,000 years before the present (Harris and Hillman 1989). Why agriculture arose during this limited time period and only in a few places, and exactly how wild plants were identified, manipulated, and managed for domestication remain mysteries. Although the origins and processes of crop domestication are obscure, its consequences are well known and thoroughly documented the creation of an entirely new way of life and eventual rise of urban civilization with all of its wonders and woes. Since the time of domestication, a progression of changes has occurred in farming systems and social systems associated with agriculture. Greater numbers of people than ever before in human history are dependent on a smaller number of crop species; a handful of “mega-crops” have supplanted locally important crops and now feed most of the world’s population (Wilkes 1995). The reduction in interspecies diversity of food plants continues the trend of exercising ever greater control over nature and the production process, a trend also supported by the increased use of manufactured inputs in crop production.

Individual social and production systems have been gradually but inexorably integrated into a single, interconnected world system of economic, cultural, and technology exchange, and this integration threatens genetic diversity of crops as much as population increase and modern technology.

Until recently, most crop production was intended for local consumption, and it relied mostly on local resources of energy and crop germplasm. Today, however, exceedingly few farming systems function in isolation from  markets, national and international political influence, and flows of capital, energy, and technology. Although most farmers still produce their own food, they also sell an appreciable amount into local and national markets. The use of non-local technology and inputs, such as fertilizers, pesticides, and mechanization, is ubiquitous. An increasingly important part of the flow of technological goods to farmers is improved crop varieties, selected from outstanding farmer varieties, developed and released by public crop improvement programs, or sold by private seed companies.

The economic, political, and technological integration of farming systems is generally seen as a positive step that enables development — increased production, income, and well-being (Hayami and Ruttan 1985). Nevertheless, this integration has several negative impacts. Farmers relinquish personal and local control of the production system as they become subject to market and political systems that are not always stable or positive for particular locations or commodities (Chambers 1983; Cernea 1985). Communities and farming systems may become more stratified economically. Increasingly uniform crops may be more vulnerable to pests and diseases. Local knowledge and crop diversity may be lost because of the diffusion of improved, exotic technology.

These negative impacts may be ameliorated by policy and technological means, although the knowledge and ability to manage the negative impacts of change are often underdeveloped. Nevertheless, it is important to note that lack of socioeconomic integration also carries potentially serious negative impacts, especially given population growth.

Cultivar diversity in association with wild or ancestral crop species is linked to crop domestication and, most importantly, a broad base of genetic resources that may be useful for crop improvement. The loss of crop varieties from centers of diversity causes genetic erosion or a loss of genetic resources — a negative consequence of agricultural development. Natural historians and biologists have long recognized that particular areas harbored unusually  diverse and rich stores of crop germplasm (Harris 1989). One contribution of N. I. Vavilov (1926) was to perceive that these stores were important resources for crop improvement. Shortly after Vavilov’s observation, it was noted that these concentrations of crop germplasm were vulnerable to loss, as technological and economic change occur (Harlan and Martini 1936). Once the stores of crop germplasm were identified, a worldwide effort was initiated, first to sample and then to conserve the genetic diversity of major food staples (e.g., rice, wheat, maize, potato, cassava, sorghum, millet, barley, common bean, soybean). The conservation effort focused on preserving crop germplasm that is held in the thousands of distinct crop varieties or cultivars. By 1980, a large portion of the estimated diversity of major staples had been collected for preservation in ex situ facilities — gene banks, botanical gardens, and working collections of crop scientists. During the establishment of the current gene conservation effort (1970-1980), in situ conservation was perceived as a possible alternative strategy for conserving crop germplasm, yet it was dismissed for several reasons (Frankel 1970). Most importantly, it was assumed that progress in achieving economic development in diverse agricultural systems inevitably requires the replacement of local crop populations with improved ones.

Because genetic diversity in crops is associated with traditional agricultural practices, it is also linked to underdevelopment, low production, and poverty.

The positive relationship between crop diversity and poverty is seemingly confirmed by the fact that agricultural development in many places and at different times occurred with the replacement of local and diverse crops, for example, in the hybrid maize revolution in U.S. agriculture between 1920 and 1950 (Cochrane 1993). A corollary of the relationship between diversity and poverty is that conserving traditional crops and their genetic diversity on-farm is tantamount to trying to stop agricultural development. Another reason for rejecting in situ conservation is the assumption that farmers who grow traditional crop varieties would require a direct monetary subsidy to continue this practice once improved varieties become available. Such subsidies are not only expensive but also unreliable and difficult to manage for any length of time. Finally, crop scientists who promoted conservation were not interested in conservation alone but also in using genetic resources for crop improvement. As long as breeders’ work is confined to experiment stations and laboratories, genetic resources that remain in farmers’ fields are not directly useful for crop improvement. Several decades of collection and gene bank storage of crop genetic resources and research on agricultural change under modern conditions have changed the views that led to the dismissal of in situ conservation in favor of ex situ methods (Maxted et al. 1997a). One important shift in attitudes is the view that in situ and ex situ methods are no longer perceived as exclusive alternatives to each other. Today, they are seen as complementary approaches rather than as rivals. There is recognition that these methods address different aspects of genetic resources, and neither alone is sufficient to conserve the total range of genetic resources that exist.


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