Document(s) 12 of 12

Introduction

On-farm conservation has been proposed as a strategy to conserve the processes of evolution and adaptation of crops to their environments (Oldfield and Alcorn 1987; Altieri and Merrick 1987; Brush 1991). The conservation of specific genes or genotypes is secondary to the continuation of the processes that allow the material to evolve and change over time, remaining adapted to local agricultural production conditions. A prerequisite, however, for evolution and adaptation is the existence of genetic variation (Lande and Barrowclough 1990; Hamrick and Godt 1997). If the continued use of local cultivars by farmers is to form part of a conservation strategy, some knowledge of the amount of this genetic variation is needed to evaluate different approaches. This knowledge needs to be linked to farmer decision making and acquired over time (Frankel et al. 1995).

In the process of planting, managing, harvesting, and processing their crops, farmers make decisions that affect the genetic diversity of the crop populations. Over time they will modify the genetic structure of a population by selecting for plants with preferred agro-morphological characteristics. Farmers will influence the survival of certain genotypes by choosing a particular farming management practice or by planting a crop population in a site with a particular micro-environment. Farmers make decisions on the size of the population of each crop variety to plant each year, the percentage of seed to save from their own stock, and the percentage to buy or exchange from other sources. Each of these decisions, which can affect the genetic diversity of cultivars, is linked to a complex set of environmental and socioeconomic influences on the farmer.

To date, the majority of on-farm conservation case studies have concentrated on linking farmer maintenance of local crop cultivars to environmental and socioeconomic factors at a particular point in time (Glass and Thurston 1978; Clawson 1985; Richards 1986; Brush 1991, 1995; Brush et al. 1992; Bellon 1996; Cromwell and van Oosterhout, this volume). These studies focus on investigating the factors that have influenced farmers to maintain or not to maintain local cultivars. In some cases, the genetic diversity of the locally grown cultivars has also been measured at a given time using genetic diversity indices of allelic richness or allele evenness within the population (e.g., Zimmerer and Douches 1991), but the primary concern of the investigation has usually been to describe the circumstances in which local cultivars constitute a part of production systems.

For the most part, the link between the effect of farmer management decisions and amount of genetic variation within the crop population has not been studied in detail. What is the effect of different farmer selection strategies on the genetic structure of the local cultivar over a number of years? What happens to the genetic diversity of local cultivars when farmers change the area planted? At what point will reduction in the area planted to a specific local cultivar lead to a significant reduction in the genetic diversity and limit further change? What is the effect on the genetic diversity of local cultivars of introducing new material or altering selection strategies through participatory breeding? These questions are important for understanding changing patterns of production and for those who advocate the use of local cultivars as components of sustainable production. They are also important questions for those who see on-farm maintenance of local cultivars as a component of a national conservation strategy. Without some understanding of the effect of farm-based decisions on genetic variation, national programs will lack the information needed to support, assist, or intervene in on-farm management of local cultivars where they see this as a part of their own conservation program. The few studies that have begun to look at the possibilities of a link between farmer decisions and genetic diversity have necessarily concentrated on one crop in one geographic area and focus on a particular point in time (Teshome 1996; Casas and Caballero 1996; Louette, this volume). For a national program to formulate a comprehensive on-farm conservation strategy, for each relevant within-country farming system, answers are needed to the questions: (1) which farmer-based decisions affect whether the amount of genetic diversity within a crop population decreases, increases, or remains stable over time and (2) where, when, and how do these decisions affect the genetic diversity within a crop population?

This chapter explores the issues involved in conserving genetic diversity through farmer maintenance and use of local cultivars. The concern is to consider the ways in which national plant genetic resources programs might address these issues. To illustrate this, we first describe the recently initiated program of work coordinated by the International Plant Genetic Resources Institute (IPGRI) which takes the form of a multidisciplinary global project to investigate on-farm conservation; to build national capacity and explore community participation in nine countries. We then discuss some central genetic questions and explore some of the implications of these for national programs concerned to maximize the diversity conserved.

Linking institutions, disciplines, and methodologies

In 1995, IPGRI, working through national programs, formulated a global project in nine countries to strengthen the scientific basis of in situ conservation of agricultural biodiversity. The objectives of the project are to:

• support the development of a framework of knowledge on farmer decision-making processes that influence in situ conservation of agricultural biodiversity
  
  
• strengthen national institutions for the planning and implementation of conservation programs for agricultural biodiversity
  
  
• broaden the use of agricultural biodiversity and the participation in its conservation by farming communities and other groups

The nine countries involved in the project are Burkina Faso, Ethiopia, Nepal, Vietnam, Peru, Mexico, Morocco, Turkey, and Hungary. In each country, strengthening the relations of formal institutions with farmers and local-level institutions to promote on-farm conservation is a major concern. These partner countries were included because each was within a region of primary diversity for crop genetic resources with worldwide importance. Each has traditional farming communities that maintain plant genetic resources. The countries all have national programs organized to conserve crop resources, which include ex situ conservation facilities, and all indicate a strong interest in developing a national capacity to support in situ conservation.

The program was formulated with the idea that in situ conservation activities should not aim to dissuade farmers from adopting new crop varieties that increase food availability or income, but rather to (1) determine and understand the situations in which local cultivars are maintained by farmers; (2) identify the key factors which affect farmer decisions to maintain local cultivars; (3) understand how farmer decision making affects the amount of genetic variation within crop populations over time; and (4) find ways to assist the continued selection of local cultivars or cultivars that conserve local germplasm. The development of any support program is expected to vary substantially across and within the different countries. The project emphasizes, therefore, participatory and learning approaches rather than the development of a specific model. The concern is to understand what is happening rather than prescribe abstract solutions.

The program supports research on the biological and social bases of in situ conservation, including (1) collecting a basic data set that links farmer decision making on the selection and maintenance of crop cultivars to measurable indices of genetic diversity; (2) training national scientists in in situ conservation research; (3) identifying target areas for in situ conservation programs; and (4) building bridges between conservationists, farmers, agricultural development agencies, and policy makers.

Three main strategies are used in project implementation: first, multi-disciplinary work in the areas of crop biology and social sciences that will create a framework of knowledge and lead to institutional strengthening, methodologies and guidelines for other in situ programs; second, community participatory breeding and agronomic work, including community and locally based conservation activities involving market development, farmer incentives, and community-based training, that will support sustainable agricultural development; and third, international coordination and scientific synthesis to create a global framework for supporting in situ conservation by farmers.

The project works through formal institutions (e.g., universities, agricultural research and conservation institutes, and stations within the ministries of agriculture, natural resources, and science and technology) to strengthen their relations with farmers and local level institutions (e.g., community-based organizations, farmer groups, and non-governmental organizations) to promote on-farm conservation. Although working through national programs may be faulted as a centralized, top-down approach, the strategies that come out of this approach are based on information that comes from the farmer.

National programs interested in on-farm conservation must cope with the objectives of (1) conserving processes which promote genetic diversity of crop resources, and (2) ensuring the improvement of living standards of the farmer. To formulate an on-farm conservation strategy, knowledge is needed on how farmer selection practices affect crop genetic diversity. This requires scientific expertise from a variety of sources. At the same time, to ensure the sustainability of an on-farm conservation program, the national program needs to understand how, when, and where a farmer continues to maintain genetic variation. Sustainable management and conservation will be most effective where the resources have concrete value in the present time, can be used to meet the needs of local communities, and will contribute to the development of the nation as a whole (IPGRI 1996). The latter information requires contact with community-based organizations, extension workers, and non-governmental organizations that work closely with farmers. Such informal organizations are also in a position to recommend strategies that will influence a farmer to continue a particular selection practice that increases the amount of genetic variation in a population or to discontinue a selection process that decreases the amount of genetic variation in a population.

It might be argued that national program support of on-farm conservation is more likely to ensure its sustainability than non-governmental organization-funded projects. Funding to non-governmental organizations from donor agencies is finite, whereas, unless a change in government occurs, government funds can continue to be allocated. However, national institutes are far more removed from farming communities than non-governmental or community-based organizations. Therefore, the key is to ensure that a national program bases its on-farm conservation strategy on farmer-based perspectives by integrating the national program with community-based or non-governmental organizations. This is a difficult task as in many countries both parties are suspicious of each other. One role an international agency can play is to support projects that bring these different partners together.

Creating a framework of knowledge to support the formulation of on-farm conservation requires expertise from a variety of fields that are not normally associated: population genetics, biogeography, conservation biology, ecology, economics, sociology, anthropology, and local or "indigenous" knowledge systems. This expertise and the associated disciplines and methodologies are usually not found in a single institute. Often, a country's agricultural research institute may lack expertise in the social sciences. A social science department of a university may lack expertise in working directly with farmer groups. Community-based organizations may have expertise in working with farmers, but not in systematic sampling and relating farmer responses to population genetics. A meaningful investigation of questions relating farmer decision making to genetic diversity maintenance will require an integrated team of disciplines from formal institutes, such as universities and national research institutes, and informal organizations, such as community-based groups including non-governmental organizations.

Implementation of on-farm conservation investigations presupposes that such an integrated framework at central and local levels already exists within the country's national program. In many countries, this is not the case and the creation of such a framework is a prerequisite to formulating on-farm conservation strategies. For the IPGRI-supported global in situ project, the first step was to support the formation of such a framework and integrated teams in the nine participating countries. This framework has consisted of the setting up of a multidisciplinary National Advising Committee, which is led by a National Project Coordinator and includes members from formal and informal institutes. The National Advising Committee serves as the lead institution in coordinating and monitoring project activities, provides technical backup, ensures integration into the national program and approves plans and reports for the regional and global management levels. In addition, technical working groups are established in biological and social sciences and in extension and training. These involve ethnic and gender groups and will technically supervise and monitor project activities. Technical support is supplied by a project Technical Advisory Committee. The way in which this is working out in practice is briefly illustrated for Morocco, Burkina Faso, and Nepal.

Morocco

Situated along the Atlantic Ocean and the Mediterranean Sea, with the Rif Mountains in the North, the Atlas Mountains running north to south, and the Sahara Desert east and south of the Atlas Mountains, Morocco contains a unique array of agroecosystems. It is a center of diversity for such worldwide crops as wheat, barley, faba bean, and alfalfa (Neal-Smith 1955; Nègre 1956; Perrino et al. 1984; Tazi et al. 1989). The country's crop diversity results from long-term adaptation to drought, cold, and saline conditions (Sauvage 1975; Graves 1985; Birouk 1987; Francis 1987; Birouk et al. 1991). Islands of crop diversity with a high dependence on local cultivars remain in mountain areas and in oases at the edge of the Sahara.

Morocco has a national program for plant genetic resource (PGR) conservation coordinated by a National Committee, which was established in 1992. The management committee for the program consists of members from nine different organizations and institutes. The National Project Committee for the on-farm conservation project in Morocco is a subcommittee of this National Committee. Formal institutes involved are Hassan II Institute of Agronomy and Veterinary Medicide (IAV) and Institut National de la Recherche Agronomique (INRA) and their associated extension and research institutes, the Agricultural Provincial Directorates (DPA) and Office Regional de Mise en Valeur Agricole (ORMVA). Hassan II IAV is involved in research in cultivated cereals and fodder crops, ex situ conservation, evaluation, genetic analysis, GIS, documentation and data analysis, socioeconomic studies, and ethnobotany. INRA is responsible for national agricultural research and includes departments for Cereals, Legumes, Soil Science and the Environment, Socioeconomics, and Genetics. The DPA and ORMVA, under the Ministry of Agriculture, are involved with local farmer contact, extension, and technology transfer. A representative from the Education Department of the Ministry of Agriculture is involved in the project for public awareness and extension work at the central level. In addition, L'Association pour la Préservation de la Biodiversité au Maroc (BELDIA), a Moroccan non-governmental organization versed in community participatory projects, is a member of the National Project Committee.

Three priority agro-ecological zones within Morocco have been selected for the project. The first is the Demnate/Tanante region, under the Azilal DPA in the high Atlas, a semi-arid area with a clay loam soil. Priority crops for this area are barley, durum wheat, faba bean, and alfalfa. The second region is the Valley of Ziz-Fafilalte, managed by the Errachidia ORMVA in the oasis area, an area of semi-desert with sandy loam soils. The priority crops here are bread wheat and alfalfa. The final area is under Taza DPA and Chefchaouen DPA in the Rif and Pre-Rif mountain area. Here barley, durum wheat, and faba bean are grown under rain-fed conditions, on a clay loam soil.

Burkina Faso

Burkina Faso sits in the Soudanian and Sahelian zones and is within the region of African crop domestication, evolution, and diversity for sorghum, millet (especially pearl millet), and cowpea. Sorghum, pearl millet, and, more recently, maize and rice occupy more than 75% of the cultivated land, while groundnut and cowpea occupy 25%. Sorrel, onion, and okra are important as vegetables in the production of sauces and as cash crops. Approximately 75% of the country lies on old Precambrian crystalline rock, with extensive areas of marginal soils. Rainfall is extremely variable, and the amount and length of season of rainfall are main factors affecting crop yields. Serious soil degradation, repeated drought, and unrestrained use of modern varieties contribute to the erosion of genetic diversity, but, in some areas, local cultivars are grown extensively.

In Burkina Faso, the Centre National de la Recherche Scientifique et Technologique (CNRST) houses key institutes and scientists who work in the area of plant genetic resource conservation and use. A national strategic plan has been developed for research, which includes on-farm conservation of plant genetic resources. CNRST has capacity both for research and to make links to farmers via protocols, which it has already signed with a number of non-governmental organizations. Two institutes are especially important for investigating the scientific basis of on-farm conservation: the Institut d'Études et Recherches Agricoles (INERA) and the Institut de Recherche en Sciences Sociales et Humaines (IRSSH). The Institut de Recherches en Biologie et Écologie Tropicale (IRBET), focusing on ecology, will soon be combined with INERA.

INERA has strong link to the national non-governmental organization, the Fédération de Unions des Groupements Naam (FUGN), a farmers' union that operates throughout Burkina Faso. In addition, two other non-governmental organizations, CRPA-Yatenga and Crocevia, operate a program on production of seeds of local varieties including African rice, sorghum, and millet. Another important member of the National Project Committee is the Université de Ouagadougou, which has both research facilities and training capacity.

Agroecological regions were selected from the three major climatic zones of Burkina Faso: the Sahelian, the North Soudanian, and the Soudanian. Research sites were also chosen for degree of population density, ranging from the more densely populated region in central Burkina Faso to the less densely populated areas in the north and southwest. In the Sahelian zone conditions are harsh: precipitation is less than 600 mm per year and soils are poorly developed. The region has a well-organized agricultural extension network in place, together with nongovernmental organization presence and farmers' organizations. In the north Soudanian zone precipitation ranges from 600 to 800 mm, population density is extremely high, and there are many farmers' organizations interested in participating in the project. The Soudanian zone selected contains the major food production area of Burkina Faso. Here the precipitation is greater than 800 mm. Soils are lateritic or hydromorphic (along the Mouhoun River), and the region is served by a strong extension program with active nongovernmental and farmer organizations.

Nepal

Nepal's location, geography, and diverse ethnic groups have made it an important center of agricultural biodiversity. Crop production takes place between 70 to 3000 m elevation, under rainfall regimes from less than 1000 mm to over 5000 mm, and on infertile to very fertile soils. Numerous ethnic groups of both Indo-Arayan and Tibet-Burmese descent, with varying cultural preferences, and different access to market, credit, and agricultural inputs, have created a diversity of agroecological systems (Upadhyay and Sthapit 1995). Food grains, such as rice and finger millet, grain legumes, barley, and minor crops, including buckwheat, have great genetic diversity. More than half of the arable land is planted to local cultivars. However, with the introduction of new high yielding varieties and over-exploitation of natural resources, genetic erosion is increasing rapidly in Nepal.

The Nepal Agricultural Research Council (NARC) is the national focal point for agricultural research in Nepal. Recently NARC has begun working with farmers through a network of regional research centers to further participation in in situ activities. Agricultural research stations such as Jumla, Lumle, Malepatan (Pokhara and Hill Crop Program at Kavre), and Parwanipur have been identified as potential partners within NARC systems for in situ activities, together with local non-governmental organizations with relevant experience (e.g., Local Initiatives for Biodiversity Research and Development, LI-BIRD). The Chief of the Agricultural Botany Division is the National Project Coordinator for the Nepal project and the National Project Committee is comprised of members from NARC, the Ministry of Agriculture, and non-governmental organizations.

Three regions of Nepal have been selected to represent high, middle, and low altitudes of crop production ecosystems in Nepal (Upadhyay and Sthapit 1995). The Jumla valley is remote and has a unique range of crop varieties finely adapted to local conditions. The area is a transition zone between lower elevations, where a winter cereal is followed by a summer crop, and higher elevations where only one crop (either winter cereal or summer crop) can be obtained. The valley is known for its cold-tolerant Jumli Marshi rice and other crops associated with rice-based farming systems. The second area, the Pokhara Seti River Valley, is known for its quality rice in the Western Hills of Nepal. It is characterized by a number of lakes, broad alluvial valleys, isolated hills, and meandering streams. Rice-wheat-vegetables and maize-millet-vegetables are major cropping systems. The valley has diverse ethnic composition, mainly Brahmin, Chhetri, Gurung, Magar, and Newar. Parwanipur, the third area, lies in the fertile strip of Indo-Gangetic plain (100 to 200 m) on the southern frontier bordering with India. The production potential is high and farmers have adequate access to inputs. The rice-wheat system is the basic cropping pattern of the region and both irrigated and rain-fed systems occur in the same communities.

Implementing integrated research on-farm

The frameworks described above for Morocco, Burkina Faso, and Nepal are similar to those envisaged for the other partner countries in the IPGRI-supported, global on-farm conservation program. Once a project management framework is in place, an initial step for each partner country has been to select regions for the work. Initial agro-ecological identification is followed by a natural and social science baseline survey carried out by a multidisciplinary team as a preliminary to specific site selection. Multidisciplinary teams are needed at the very start to evaluate if the initial agroecological zones selected meet mutually agreed-upon criteria, such as the existence of genetic diversity, desired agroecological variation, accessibility to the locality, links to agricultural extension work, and, most importantly, interest and cooperation of local communities. In Nepal, for example, multidisciplinary teams have been formed at the national level and are planned for each agroecological site. The national level team consists of agroecosite managers, one from each of the three agroecosites, a crop biologist, a social scientist, an ecologist, a gender specialist, an outreach specialist, and a participatory plant breeding specialist. Similarly, local teams are planned for each of the three agroecological sites. In Morocco, the team consists of specialists from the national research system and Hassan II University in each of the priority crops, soil science, socioeconomics, and genetics, together with staff from the national agricultural extension and outreach program and the nongovernmental organization, BELDIA. In each country, once members of each team are identified at the national and local level, the actual selection of project sites and farmer participants becomes an interactive process between researchers, agricultural extension workers, and the farm community.

Preliminary to baseline data collection and site selection, training of local extension agents/non-governmental organizations and scientific research workers is needed in participatory approaches, semi-structured interviews, identification and use of key informants, gender sensitivity, and other aspects of gathering socioanthropogenic information. Likewise, both social and natural scientists participating in the research should receive some basic orientation on population genetic concepts, and on the ecological data required. In Nepal and Burkina Faso, workshops are being organized for geneticists, ecologists, social scientists, and community-based staff, as well as with community representatives and participating farmers, to develop an understanding of the data needed and the work envisaged.

The objective of the information-gathering component of the project is to develop a set of data that can be used to answer questions about on-farm maintenance as a conservation process. It is designed to explore the links between environmental features, farmer decision making, and the genetic diversity maintained over time in local cultivars. One key area on which it is hoped to obtain information is the link between farmer-based decisions and the extent and distribution of genetic diversity in local cultivars in the study areas. Five aspects of farmer decision making seem likely to be of most importance: (1) decisions on what agro-morphological characteristics are important to the farmer in any selection procedures used; (2) decisions on what farming practice to use on the local cultivar population; (3) decisions on where to plant the population; (4) decisions on the size of the population to plant; and (5) decisions on the seed source for the population. It is hoped to establish the effect of these decisions on the genetic diversity of the different populations studied over time.

Agro-morphological characteristics

Local cultivars are normally defined by farmers in terms of their agro-morphological characteristics (Zimmerer and Douches 1991; Weltzien et al. 1996; Sthapit et al. 1996b; Louette and Smale 1996; Teshome 1996; Louette et al. 1997). Depending on the crop, a farmer may decide to select and maintain plants based on preferred agro-morphological criteria, such as early flowering, height, denseness of inflorescence, or a particular color, shape, or taste (Boster 1985). Some of these characteristics may be controlled by single genes but most are controlled by many loci, as in the case of most yield-related characters. A first set of questions concerns the way in which character or performance based selection by farmers influences the overall genetic diversity of the population as well as that of the characters of concern to the farmer. Farmer-based selection, even experimentation (Richards 1986), is often very important but may not always be so (Ceccarelli and Grando, Chapter 3, this volume), and may be concerned primarily with maintenance rather than change (Bellon et al. 1997). In any integrated studies, on-site observations will also be needed to investigate whether there is introgression between crops and their wild relatives and whether these are noted and retained (or discarded) by farmers (Jarvis and Hodgkin 1996). In Burkina Faso, the national program is currently conducting studies on the natural introgression of wild and cultivated pearl millet.

A second set of questions relevant to farmer selection of preferred agro-morphological characters is: does the farmer-based selection process change over time in accordance with changes in environmental or socioeconomic conditions, and, if so, under what conditions? Where changes in the selection process occur, the extent of any associated changes in the genetic diversity of the population over time needs to be investigated.

The approach proposed in the IPGRI global project is to first ask farmers to list the agro-morphological characteristics used to distinguish a crop variety, and then to prioritize the characteristics he or she selects each year. Selection of plants or seeds with priority agro-morphological characteristics may be made in the field throughout the growing season or after harvest. The selector may be male or female, young or old. Collection of selection criteria, therefore, may need to be acquired separately for different gender and age groups for it to be meaningful. Based on the above information, researchers can then select, sample, and measure within populations of each selected variety over time and space: (1) those characteristics prioritized by farmers that are known to be heritable and easily measurable; (2) other heritable agro-morphological characteristics that are not purposefully selected for by the farmer; and (3) selected biochemical and molecular markers, depending on the capacity of the national program carrying out the research.

Farming management practices

Farming management practices include land preparation, planting, thinning and weeding, fertilizer application, pest control, irrigation, harvesting, and post-harvest processing. Each of the processes mayor may not affect the amount of genetic diversity of the crop population over time (Snaydon 1984). Different levels of fertilizer application or the use of organic rather than chemical fertilizer may select for different genotypes in a population (Silver-town et al. 1994). Irrigated and non-irrigated populations of faba beans in Morocco have different population genetic characteristics (Sadiki 1990). Dense planting to reduce weeding and post-harvest storage of seeds also play a selection role on seed survival and the continuation of subsequent traits in the next generation.

Key questions for national on-farm conservation programs are (1) which farming management practices influence genetic diversity and (2) to what extent do these practices affect the amount of genetic variation in the crop population. For national programs to look at these questions, interviews and observations of farmer management practices are needed. Field trials using different degrees of density or fertilizer application coupled with measurements of genetic diversity may be desirable to investigate specific effects of particular treatments. Such studies may, however, lie outside the capacity of this particular project and be best explored in specific case studies.

Environmental selection

When a farmer decides to plant a cultivar on a particular micro-site, the crop population is exposed to specific environmental selection. By planting barley in soils prone to water logging or in different agroecological sites, the Ethiopian farmer is subjecting the plants to environmental selection for tolerance to a specific stress (Demissie and Bjornstad 1996, 1997). Similarly, by planting upland "Jumla" rice at elevations up to 3000 m in Nepal, or "Chao" rice on shallow soils in northern Vietnam, the farmer is exposing a crop population to cold stress or poor soil conditions.

Questions under this selection category revolve around (1) how environmental selection has influenced the genetic diversity of the population over time and (2) which environmental conditions playa significant role in affecting the amount of genetic variation in the crop population. The farmer's involvement is in making the decision to plant that particular population in a particular micro-habitat.

To answer these questions, national programs will need to focus on basic questions of ecological genetics, to understand how populations adapt to their environments, and to determine the type and extent of effect of environmental factors on the amount of genetic variation over time (Merrell 1981; Allard 1988, 1990; Fowler 1990; Real 1994; Le Boulc'h et al. 1994; Goldringer et al. 1994). The extent to which farmers maintain unique types for particular micro-environments will be important, as well as the occurrence within local cultivars of G × E interactions or broad tolerance of a range of stress environments (Huenneke 1991; Via 1994; Anikster et al. 1997). Social scientists' involvement will be in investigating what factors influence a farmer to plant in the particular habitat (Bellon and Taylor 1993; Bellon and Brush 1994). The work will likely point to specific studies over longer periods that will help breeders and users understand the nature of adaptation in local cultivars.

Population size

The size of a population planted by a farmer will affect the amount of genetic variation of the crop population over time (Shaffer 1990; Lande and Barrow-clough 1990; Barrett and Kohn 1991). The smaller the population, the more likely it is that genetic drift, inbreeding, loss of alleles, and stochastic events will affect the population (Shaffer 1990; Frankel et al. 1995; Slatkin 1987, 1994). From a conservation perspective, crucial questions include: How does population size influence the genetic diversity of the local cultivar population? What is the effective population size that ensures long-term stability of the population? Should a national program be concerned with a group of smaller populations or metapopulations, or should the conservation focus be on individual farmer fields? To understand the effect of size on the amount of genetic variation of a population requires minimum population viability studies and population genetic methods (Menges 1991; Caballero 1994).

Seed source

A farmer makes a choice each year on what percentage of his or her own seeds to save and plant and what percentage he or she will acquire from other farmers. How do migration (influx of new seeds) and bottlenecks (reduction in the number of saved seeds) affect the genetic diversity of the population over time? Louette and Smale (1996) have shown that after six crop rotations of the farmer studies in Mexico, only 48% of the seed material remained from the farmer's original stock. This is the information that a population geneticists will need to determine effective population sizes (Levin 1984; Louette et al. 1997).

Again, the question of whether a metapopulation should be the unit of concern for national conservation programs is important (Henry et al. 1991; Louette, this volume). This involves social scientists and community-based groups developing an understanding of the seed supply system in order for plant geneticists to be able to determine the effective population size for the cultivar in question (Friis-Hansen 1996; Cromwell 1996). This requires knowledge, not only of seed source and informal seed supply systems, but also of how different storage systems influence the survival of different seeds over time (Kashyap and Duhan 1994).

On-farm data for conservation and use

On-farm maintenance of local cultivars is currently being promoted as a strategy to conserve genetic diversity and as a process that will secure the continued availability of genetic variation while ensuring the continuing betterment of farmer livelihood over time. In the past, most conservation workers have focused largely on ex situ conservation, with the expectation that local cultivars maintained over the centuries will shortly disappear. This is now seen as an oversimplification of the complex issues at play (Louette, this volume). Knowledge of the processes involved in farmer selection and maintenance of crop cultivars can be used by national programs to make decisions on where to support, assist, or intervene to promote the conservation of genetic diversity and strengthen the effectiveness of conservation. How can this same information, linking farmer decision making to genetic diversity, be used to help national programs improve the livelihood of the farmer? To be maintained by farmers, crop genetic resources must have value to them and must retain this value and be competitive to other options a farmer might have, or even better, to increase this value such that it is reflected in an increase in a farmer's standard of living.

Value may be added to crop resources in two main ways: the material itself may be improved or the demand for the material or some product may increase. One option is to seek improved quality, disease resistance, yield, taste, or other farmer preferred characteristics, through decentralized breeding activities (Ceccarelli et al. 1996; Eyzaguirre and Iwanaga 1996; Joshi and Witcombe 1996; Sthapit et al. 1996a, Sthapit et al. 1996b; Witcombe et al. 1996). Sthapit, Joshi, and Witcombe (1996a) have shown that, by utilizing farmers' knowledge, acceptable varieties can be bred with minimum use of resources in the high altitude areas of Nepal. Effective support for farm based maintenance needs to explore the ways in which this can best be done and the impact it has on the extent and distribution of genetic diversity.

Value can also be added to crop resources by better processing, storage, and marketing, where the farmer receives more benefit from the final product. An important role for community-based organizations and nongovernmental organizations is the formation of farmer cooperatives and farmer-managed community seed banks to maximize returns to the farmers themselves (Worede 1992, 1997; Gaifami 1992). Government policy may also playa role in ensuring that farmers' inputs and seeds receive the same or better market treatment and government support as improved varieties (Leskien and Flitner 1997; Qualset et al. 1997).

Conclusion

The majority of early studies on on-farm conservation have focused on trying to determine what factors have caused a farmer to maintain or not maintain a diversity of local cultivars. Other studies have looked at the amount of genetic variation of these cultivars at a given moment in time. The research discussed in this chapter aims to take earlier studies further by attempting to quantify over time how specific farmer-based decisions may determine both the amount of genetic variation and the effective population size of a cultivar population over time.

Changes to the amount of genetic variation can be measured as can the effect of farmer-based management on the effective population sizes. Genetic variation may be linked to farmer decisions in five major categories: agromorphological characteristics, farm management practices, planting location, size of the population, and seed source. These decisions in turn are based on environmental and socioeconomic influences. The first link forms the basic data set for the second link. Understanding these processes requires the involvement of people from informal and formal institutes and from a variety of scientific disciplines. Once there is better knowledge of these processes, national programs will be in a better position to support, assist, or intervene in the conservation of genetic diversity on-farm.

Farmers themselves will ultimately determine the extent to which on-farm maintenance of local cultivars continues and, hence, contributes to the overall conservation of crop genetic diversity. Previous conservation work underplayed or even ignored this contribution and emphasized ex situ methods of diversity maintenance. Through the creation of a framework of knowledge of the processes involved, it is hoped to provide a more complete understanding that redresses this imbalance.

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