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CHAPTER 12 Local Management of Biodiversity in Traditional Agroecosystems Robert E. Rhoades and Virginia D. Nazarea CONTENTS Introduction Historical Perspective on Agrobiodiversity Strategies for In Situ Agrobiodiversity Conservation by Indigenous Communities Multidimensional Criteria for Selection and Maintenance of Landraces Comparison of Scientific/Formal Approaches to Biodiversity Maintenance Social, Economic, and Political Dimensions of In Situ Conservation The Social Context of Community-Based Biodiversity Management Global Change and Plant Genetic Resources Pathways Toward the Future References INTRODUCTION The development goal of increased food and fiber production to match the needs of growing populations and their rising expectations may often conflict with the in situ conservation goal of preserving plant genetic diversity (Williams, 1986; Alcorn, 1991). As broadly adapted high-yielding varieties — coupled with input packages © 1999 by CRC Press LLC. of irrigation, fertilizers, and pesticides — find their way into traditionally diverse, marginal agroecosystems, the number and diversity of local landraces as well as associated local knowledge may erode. This process is global, although its dynamic and intensity may vary from place to place and across time (Ford-Lloyd and Jackson, 1986; Oldfield and Alcorn, 1991; Brush, 1992; Dove, 1996). One of the premises of sustainable agriculture is that this trade-off between increasing productivity and loss of biodiversity is not inevitable (National Research Council, 1992; Thrupp, 1997). Precisely how the two goals are simultaneously achieved, however, is not an insignificant research problem or an easily answered policy issue (see Williams, 1986). Present demographic and economic global trends require more food per unit area and unit time, but the necessary yield increases will not be forthcoming unless sufficient biodiversity is continuously available to plant and animal breeders. Our primary thesis is that one useful but neglected strategy to achieve sustainable food production lies in supporting traditional in situ biodiversity management. We argue that many local populations have historically managed biodiversity, that the associated knowledge is valuable and irreplaceable, and that both management practices and knowledge should be enhanced through policy and technology initiatives. Specifically, we address our thesis by exploring three major themes related to indigenous management of germplasm and the potentialities for the localized creation, maintenance, and enhancement of biodiversity. First, we place biodiversity management by traditional agroecosystems in global historical context, especially as it relates to the major food crops. Second, based on our own research experiences we outline some principles of in situ biodiversity maintenance within traditional, marginalized agroecosystems and contrast these to the scientific, ex situ approaches of formal, external input-dependent and market-linked approaches. Third, we examine the social, economic, and political dimensions of marginal communities managing in situ agrobiodiversity. Finally, we conclude with some observations on future research and action needs. HISTORICAL PERSPECTIVE ON AGROBIODIVERSITY Landrace-based genetic materials available for plant breeding or biotechnology programs have already been purposely manipulated by traditional cultivators over centuries and even millennia (Ucko and Dimbleby, 1969; Struever, 1971; Altieri and Merrick, 1987). Although archaeological debates continue over precisely where and how nomadic hunters and gatherers finally began the conscious planting of seeds, roots, or tubers and thereby ushered in the “Agricultural Revolution,” the outcome of early farmers’ efforts cannot be denied (Hobhouse, 1985; McCorriston and Hole, 1991). The historic tendency for preindustrial agricultural communities has been to foster and increase landrace diversity, rather than decrease it (Harlan, 1995). As long as 8 to 12 thousand years ago, “primitive” farmers had already successfully experimented with invading wild “weedy” species in their settlement clearances and domesticated the first crops (Harlan, 1975). Not only did prehistoric cultivators give humanity the major food crops and animals which nourish us today, © 1999 by CRC Press LLC. they simultaneously created their own specialized knowledge systems about the food, fiber, and medicinal values of thousands of plant and animal species (Schery, 1972; Fowler and Mooney, 1990). While modern science has been appreciative of and concerned about the supply of the genetic raw material provided by farmer curators, much less interest has been shown in the local knowledge or management strategies which underpinned in situ landrace development in the first place (Nazarea-Sandoval, 1990). De Candolle (1885) and later Vavilov (1926; 1949) were the first to observe that the density of interspecific and intraspecific variation of crop species was found in “centers of domestication” which tended to be in the ecologically complex mountainous regions or areas of marked dry–wet seasons in Africa, Asia, and Latin America (Rhoades and Thompson, 1975). Due to a variety of causes, major ancient civilizations — such as the Andean, Mesopotamian, Mesoamerican, Indus, and Chinese — evolved near these centers in close association with diverse plants and animals. In complex ecological settings under conditions of human population expansion, the coevolution of human culture and plant populations led to a level of people–plant interdependency so high that some modern crops — such as maize — cannot even reproduce themselves without purposeful human intervention (Iltis, 1987). The historical and ethnographic records are rich with data on how cultural knowledge intertwines with the biological to the degree they cannot be separated and still maintain dynamic evolutionary-ecological systems (Nazarea, 1998a). This detailed knowledge not only focused on production but also storage, processing, cooking, and utilization qualities needed for the survival and rejuvenation of crops and humans (Nazarea-Sandoval, 1992). As a result, domesticated crops can be understood as culturally created and conceived human artifacts — valued for multiple qualities such as utility, taste, color, shape, and symbolism (Zimmerer, 1991). Indeed, foods or other materials derived from crops or animals are not just calories for the human body but are integral parts of daily social and cultural lives (Brush, 1992). The original diversification of crops in the centers of domestication was further enhanced after the Age of Discovery when plants were transferred by explorers between the Old and New Worlds (Hobhouse, 1985). In their new homes, migrating plants were further manipulated by curious cultivators and horticulturists who tested the exotic materials, selected those that did well, and then integrated them into their local farming and gardening systems. However, problems in the transplanted plants soon became evident. Since only a small amount of the genetic variability found in the agroecosystems of domestication made it to the new environments, resistance to disease and pests was often lacking and collapse under the onslaught of disease or pests was devastatingly frequent (Rhoades, 1991). The most famous documented case is that of the widespread potato crop failure in mid-19th-century Europe due to late blight (Phytophtera infestans), a fungus likely introduced from the Americas. Most of Europe had come to depend on a few varieties; in Ireland there was total dependence on a single variety. Combined with political exploitation by the British government, the unfortunate timing of the crop failure led to the deaths of millions of Irish (Woodham-Smith, 1962). A few years later, the grape crop on mainland Europe succumbed to a minute, aphidlike insect (Phylloxera vitifoliae) accidentally introduced from wild American grape stock (Vitis labrusca) (Olmo, 1977). These © 1999 by CRC Press LLC. two incidents spurred a tremendous interest on the part of European scientists to understand not only the nature of disease (plant pathology was born of these efforts), but also the relationship among the centers of genetic origin, natural range of variation, and disease resistance. Although neither Mendelian genetics nor the theory of disease was understood by the 1870s, European farmers appreciated that “renewed” seed stock from the regions where the crops originated brought bloom back to their crops. In the case of postfamine potatoes, a single small Andean tuber direct from South America fetched its weight in gold, thereby creating a potato seed craze as intense as the tulip craze in Holland in earlier times (McKay, 1961). Likewise, European and American plant scientists came to appreciate the link between the well-being of their farmers’ crops and the genetic diversity in the homelands of the crops themselves. Although the importance of genetic material from the centers of diversity and domestication remains highly appreciated by geneticists and crop scientists, there is less awareness of the curator role of extant farmers or pastoral communities and their knowledge which makes it possible for this valuable diversity to be maintained in situ and passed on to the global human family. Historically, most governments have seen marginal tribal and peasant communities as practicing a backward, primitive agriculture ripe for “modernization” through information and technology (Rogers, 1969). As industrial developments in Europe, North America, Japan, and the cities of the Third World attracted wage labor from the countryside, planners and agricultural scientists sought ways to provide cheap and abundant food for the growing urban areas. This cheap food policy, which has intensified in the post–World War II era, meant that the potentially productive agroecological zones (flat, fertile, and hydrologically favorable) were to become targets of planned agricultural change to make them more productive through genetic uniformity and mechanization of the agroecosystem for the purpose of achieving higher yields. One outgrowth of this simplification of the agricultural landscape was the renowned “Green Revolution,” which combined scientific plant breeding with input packages for favorable environments (Plucknett et al., 1987). The dramatic increases in world food supply witnessed in the 1960s and 1970s are directly traceable to these crop improvement programs which focused on increasing the productivity of plants though breeding for high response to inputs such as fertilizer (Mellor and Paulino, 1986). The role ascribed by scientists to local cultivators and their communities during the Green Revolution was that of recipients of “technological” packages of improved seeds, fertilizers, and other inputs, as well as infrastructure development. “Transforming traditional agriculture,” as Nobel Peace Prize–winner Theodore Schultz (1964) called the effort, was promoted as the motor for global growth and the most efficient exit from agricultural stagnation and famine. Farmers were seen as individual rational decision makers who only needed to be provided the necessary inputs and knowledge by governments and scientists to get the job accomplished. Hence, breeders made selections and crosses from advanced breeding lines derived from landraces. These lines were tested on experiment stations or controlled farm conditions, and, after a dozen or more years, these materials were released to farmers through certified seed programs, extension efforts, and other mechanisms (Duvick, 1983). Rather than breed for local conditions, breeders aimed for broad adaptability © 1999 by CRC Press LLC. of high-yielding fertilizer-responsive varieties in irrigated, fertile zones. Feedback from farmers in on-farm trials rarely provided information on the suitability of selection for specific locations. The seeds were delivered to farmers largely through the patron–client extension model which focused on the individual farm enterprise, not the community or social groupings of farmers (Duvick, 1986). The “success” of the Green Revolution was double-edged. Signficant increases in food production were achieved in a short time, leading to the alleviation of food shortages and famine in critical areas (Mellor and Paulino, 1986; Plucknett et al., 1987). However, with this success (along with other forces such as urbanization, out-migration, grazing) and as farmers responded to markets, growth, and development programs by adopting a few high yielding varieties, many landraces were abandoned. Concern over genetic erosion by national and international agencies has led to the creation of a global network of ex situ gene banks and living collections where landraces and wild materials are kept in short- and long-term seed storage (Plucknett et al., 1987). Fewer resources, however, have been given to support in situ conservation by native communities, and even less attention has been aimed at preserving the knowledge of local peoples regarding plants, a critical legacy just as vulnerable to erosion (Nazarea, 1998a). This historical ecological–evolutionary trajectory of traditional in situ management of landraces underscores the following points: 1. The often controversial proposal to maintain the dynamic evolutionary management of landraces within traditional landscapes is based on the historical reality of marginal farmers as folk curators; 2. Despite the tendency of modern agricultural science to separate the genetic “resources” from the local knowledge base, both are essential components of in situ maintenance of diversity and, by extension, a well-supplied ex situ system; and 3. Despite the loss of diversity in the “favored” environments, rich gene pools still exist in many farming communities which survive along the margins of the world economic order. These marginal rural populations are often seen — even by conservationists — as a threat to biodiversity in protected areas and surrounding buffer zones. Our approach is to see them as part of the solution. STRATEGIES FOR IN SITU AGROBIODIVERSITY CONSERVATION BY INDIGENOUS COMMUNITIES Over the years, we have spent a great deal of time working with subsistence farmers in Asia, Latin America, and the American South (Nazarea-Sandoval and Rhoades, 1994). We have studied these “native curators” intensively as anthropologists, worked with farmers as members of interdisciplinary teams at International Rice Research Institute (IRRI) and International Potato Center (CIP), and — more recently — as anthropologists attempting to document and revive landrace use in the southern U.S. through support of traditional means of use and exchange of heirloom varieties. Whether Andean farmers, Filipino rice cultivators and sweet potato growers, or Appalachian gardeners, they share common characteristics. Universally, regions of rich biodiversity exist along the margins of their economic and © 1999 by CRC Press LLC. political worlds. Landrace cultivators are typically found in more remote mountains, islands, rain forests, or desert agroecosystems which are momentarily insulated from the dominant forces of the outside world economy (Dasmann, 1991). Communities — and households within communities — with a propensity to maintain diverse systems tend to be disenfranchised from the dominant order surrounding them. Even the individuals who tend to be key native curators are marginal within their own households. Thus, marginality at various scale levels is a key common designator of landrace in situ curation. Agroecologists, along with ethnoecologists who focus on the cognitive underpinnings of human–biological system interactions, have pioneered studies which show that farmers pursue various strategies in using biodiversity as a way to meet their basic physical, social, and spiritual needs (Hecht, 1987; Oldfield and Alcorn, 1991; Nazarea-Sandoval, 1995). This body of research points to fundamental differences between informal and formal models of genetic resource/biodiversity management (Altieri, 1987; Altieri and Merrick, 1988). First, traditional producers/communities use a different set of selection and evaluation criteria for germplasm management than modern breeding or commercial seed programs. Second, their methods of experimentation and testing are fundamentally different, although there are some points of common interest. Third, the strategies which preserve biodiversity are often embedded in community action which channels and encourages individual households to act in such a way as to foster biodiversity. Multidimensional Criteria for Selection and Maintenance of Landraces Scientists find the tremendous diversity of landraces in marginal agroecosystems useful and valuable in developing new and better varieties. To the practicing subsistence farmer, however, it is strange — probably inconceivable — that one would be so foolish as to risk this diversity with the narrow selection of just a few varieties and species. In maintaining a wide range of varieties and species, traditional farmers use multidimensional decision-making criteria which holistically involve ecology, the complete food system from seed handling to consumption, and cultural aspects such as culinary qualities, ritual, and cosmology. This complex decision-making process may often be poorly understood by the formal scientific sector which tends to be largely market oriented. Farmers opt for an adaptive strategy of using biodiversity in such a way that it spreads production risk and labor scheduling across the landscape. In the Cusco Valley of Peru, for example, we found farmers who plant up to 50 different varieties as well as several species of potatoes at different time intervals in 20 to 30 scattered fields characterized by different altitude, soil types, and orientations to the sun. This principle of diversity to spread risk is simply an Andean version of “don’t put all your eggs in one basket.” This dispersion pattern reduces the risk that one disease outbreak or an unpredicted frost will devastate an entire crop. Simultaneously, by using different varieties a continuous flow of production through time and space can be realized so that different markets, household needs, or labor supplies can be accommodated. Interspecific and intraspecific variation is also used for agronomic control of weeds and pests, microclimatic variation through shading, as well as a © 1999 by CRC Press LLC. buffer against climatic and pest damage. Andean potato farmers’ strategies are based on a long-term, detailed knowledge of specific plant–environment interaction. Any variety is tested against several seasons of variable frosts and rainfall as well as performance in different soils. In the Philippines, market forces are as salient as ecological factors in farmers’ decision-making frameworks, and the cognizance of instability and unpredictability of both leads to constant experimentation, information and germplasm exchange, and hedging. A sweet potato farmer in Bukidnon resists the pull toward monoculture because of his perception that environmental flux and economic trends are beyond his control. According to him, I ask for different planting materials from our neighbors but I don’t mix them up. I plant at least five different varieties of sweet potatoes at any one time to experiment from which ones I get the most benefit. At different seasons, we should plant different varieties because we never know which ones would be most productive (Nazarea, 1998b). Some rice farmers, integrated as they are to the market system and credit infrastructure, still plant their favored varieties in the middle of clumps or at the borders of agriculture extension and credit-backed varieties, thus managing to have their credit, and eat, too. In localized agroecosystems, household production units are also direct consumption units; thus, they have a vested interest in carefully linking production and consumption in a way not found in commercial systems where different activities are typically carried out by separate groups. In subsistence systems, the household unit manages all stages of the food system, including seed selection, production, storage, processing, and marketing. Even when there is a need for interhousehold exchange of genetic material, the linkages are generally along kin-based and community networks. There are no “formal” seed certification systems and the people who select cultivars are the same ones who grow, process, store, eat, and exchange/sell them. When the consumption unit and the production unit are coterminus, a more-refined and more-detailed set of criteria is used compared with when these two functions are separated. In the Andes, an interdisciplinary research team from the CIP discovered some 39 criteria that farmers consider in their evaluation of varieties (Prain et al., 1992). This led to the conclusion that farmers do not seek an ideal variety. Instead, farmers seek to manage an ideal range of varieties that address their food system requirements related to cash and subsistence needs (Prain et al., 1992). These requirements were highly local and specific to household needs. In one of the research sites, for example, farmers would grow “improved” varieties for subsistence while in another village farmers cultivated folk varieties for the marketplace (Bidegaray, 1988). These unexpected uses were tied to certain local realities which only the farmers fully appreciated. In one case, there was a shortage of land and wage opportunities so they used their land to produce high-yielding varieties for food, while in the other case, a nearby market provided higher prices for the valued native varieties (Brush, 1992; Prain et al., 1992). © 1999 by CRC Press LLC. Another aspect of diversity maintenance involves postproduction activities (storage, seed selection, processing, and cooking). Women, who are often in charge of these nonfield activities, handle materials in such as way as to increase aspects of diversity further. Shapes and colors proliferate in landrace material since these are used as perceptual signals for sorting and identification. Most published research on potato selection makes reference to the significance of differences in color, shape, texture, and taste. Selection for “storability” or “culinary quality” occurs in the hands of women who are acknowledged by the men to have superior knowledge of the crop. Andean farmers are connoisseurs of potatoes which they evaluate with a wide range of cooking descriptors as well as taste labels such as “flouriness,” “stickiness,” “wateriness,” and so on. Native potatoes are universally recognized as superior to improved varieties in terms of culinary quality. Among Philippine sweet potato farmers, characteristics such as cooking quality, aesthetic appeal, storability, and propensity of mixing well with other cultivars are valued as much as yield or disease resistance by households surviving in the marginal zones. Morphological, gastronomic, life habit attributes, familiarity gradients, and functional criteria were used in distinguishing and prioritizing among varieties, and were far from being mutually exclusive. Interestingly, local criteria for evaluation of sweet potato varieties tend to be fuzzy or to trail off into gray areas as to which properties or traits are positive or preferred and which ones are negative or not preferred. For example, people would say they prefer sweet varieties but bland ones are good to eat with fish and are a good substitute for rice during lean times, or that newer varieties are desirable because they produce bigger roots but older varieties produce tastier though smaller roots. The result of this “fuzziness” is that it is impossible to construct a hierarchy of sweetpotato varieties from the most desirable to the least, and, as a consequence, people retain different varieties in their farms and home gardens. Another dimension of genetic resource diversity in traditional societies often overlooked by scientists and planners from more “utilitarian” urban-dominated societies is the interconnectedness between plants and cosmology, that part of culture which deals with perception, ritual, religion, and worldview. Given the intimacy of daily contact between cultivators and their biological environment, especially plants and animals, a cultural interplay is not uncommon during which the domesticates are assigned significant symbolic roles in the lives of the people themselves (Zimmerer, 1991). Therefore, plants are more than just food. Plants are also ascribed gender, spiritual qualities, mystical powers, and important religious roles in the lives of the people (Down to Earth, 1994). People of many cultures believe they originated from certain sacred plants (e.g., Mayan creation story and maize). In the case of southwestern Native American groups, the diversity of maize types (and colors) reflects group relationship, ethnic origins, cardinal directions, and a reverence for diversity (Ford, 1984; Sekaquaptewa and Black, 1986). Evidence from many cultures around the world points to a playfulness and appreciation of landrace diversity as expressed not only through color and shape, but also reflected in complex folk taxonomies and cultural identity related to landraces. In the Andes, certain potato varieties are valued more for their symbolic role in gift exchange and honoring guests at ritualized meals than for any agronomic and © 1999 by CRC Press LLC. economic values. Brush (1977) reports that the most highly prized varieties are often the most delicate and least productive (see also Carter and Mamani, 1982). One study from Bolivia pointed to the importance of potato diversity to the cultural identity of the Aymara (Johnsson, 1986). In some parts of the Andes, the most prestigious meal one can serve is made up of native cultivars, especially of potato. Although such beliefs are frequently disregarded by scientists as superfluous, the ethnographic record shows that such beliefs play a major shaping role in creating variability among cultures (Zimmerer, 1991). Try as we might, as scientists, to coax the fan of strategies into a logical, universal framework, none seems to provide greater exploratory power than the “framework” of expediency — of hedging, making do, and muddling through. By this, we mean the development and maintenance of plant genetic diversity in local agroecosystems based on day-to-day pragmatic concerns and the natural inertia that preserves diversity due to the existence of a multiplicity of local demands and preferences but cannot be fully satisfied by any one “ideal” or “best” variety. The decision-making process, in other words, is characterized by conflicting demands, complementation, and compromise, resulting in behavioral outcomes that augur well for the maintenance of a wide variety of cultivars. Comparison of Scientific/Formal Approaches to Biodiversity Maintenance Contrasting the approaches of traditional farmers and scientists in methods of varietal selection can clarify the reasons plant-breeding programs often fail to reach farmers with new genetic materials (Berg et al., 1991). Since traditional farmers deal with holistic systems and multiple selection criteria they do not normally think in terms of formal dichotomies like “improved” vs. “local” varieties. Farmers select varieties that perform well in certain areas (e.g., agronomic, yield, marketability, culinary) important to the context of their localized food system. Although farmers do not use the agronomists’ multiple replications side by side, the folk selection process is far from haphazard. Like breeders, traditional farmers have a systematic way of seeking and integrating materials into their living, working informal gene banks. Farmers are fanatic seekers of new varieties, and they will eagerly seek materials wherever they can be found (e.g., formal seed programs, neighbors, markets). Once a new variety is obtained, it is generally planted on a small scale in a kitchen garden or in a single row along the margins of a regular field. If the variety proves itself, farmers amplify their production as the amount of seed allows. The variety is observed and evaluated for multiple qualities relevant to the local food system (see Table 1). All the while, they continue to maintain their own “germplasm” bank which is constantly being replenished and experimentally culled (Rhoades, 1989a). Many farmers are avid experimenters by nature (Richards, 1985; Rhoades and Bebbington, 1995). The “atmosphere of experimentation” which characterized the neolithic farmer since the earlier stages of cultivation is one of the foundations upon which agriculture advances (Braidwood, 1967), and farmers are as creatively involved in this ongoing process as are scientists. A key difference, however, between © 1999 by CRC Press LLC. Table 1 Breeders’ and Farmers’ Cultivar Selection Methods Breeders 1. Genetically uniform cultivars (pure lines, clones, hybrids) 2. Test under ideal conditions 3. Yield and disease/climate tolerance 4. Widely adapted; agroecological target zones (flat, irrigated, fertile, homogenous, inputs) 5. Formal structures; highly centralized; top-down 6. Negative attitude toward G × E Farmers Genetically diverse cultivars Real-world conditions Multiple criteria; fuzziness Niche-specific (rain-fed, poor soils, inaccessible, local inputs) Informal; kin/community based; gendered Positive attitude toward G × E formal and informal cultivar selection is that breeders tend to narrow the genetic alternatives in search of yield and disease or climatic resistance while marginal, subsistence farmers tend to broaden their choices by seeking more diverse varieties to fit their overall needs (Soleri and Smith, 1998; Nazarea-Sandoval and Rhoades, 1994). Indigenous cultivators do not design, perceive, or manage plots or zones in isolation of surrounding areas. To the contrary, they manage for diversity along continuous boundaries by pursuing opportunities creatively to mix genetic resources and inputs to meet their household and community needs. Farmers use diverse criteria in selection and adoption decision making which does not necessarily end up with the intentional elimination of “less desirable” options. What is desirable or not desirable to local farmers may be a matter of taste, a matter of timing, and sometimes a matter of mood. In other words, they use fuzzy multiple criteria; if not, the diverse cultivars would likely have disappeared long ago (Nazarea, 1996). One of the reasons that small farmers in marginal environments have benefited little from the yield and disease resistance achieved by formal breeding programs is precisely because of the real-world interaction between genotype and environment (G × E). Breeding programs typically assume agricultural scientists know better than farmers the characteristics of a successful cultivar (Witcombe et al., 1996). Breeders select under favorable growing conditions, and, if adoption does not occur, the cause is frequently assumed to be ineffective extension or insufficient seed production (Ceccarelli, 1995). Breeding for broad adaptation to agroecological zones requires large-scale centralized seed production and distribution which in turn further promotes genotypes that might be inferior to the landraces they are replacing under stressful conditions. This formal approach contrasts with that of marginal farmers who have traditionally relied on a strategy based on both intraspecific diversity (crop mixes and landraces on the same farm) and where seed is produced either on the farm or obtained from neighbors through community-based informal seed networks. In bridging the gap between breeding programs and farmers in marginal areas, breeders have begun to think innovatively about marginal farmers, experimental designs, field plot techniques, and landraces (Maurya et al., 1988; Galt, 1989; Ceccarelli, 1995). As a result, participatory breeding programs have begun to emerge in which farmers are encouraged through support and partnership with scientists to exchange knowledge and test, under farmer experimental conditions and designs, cultivars early in the breeding-selection process (Prain et al., 1992; Joshi and Witcombe, 1996). These participatory programs have already generated varieties that © 1999 by CRC Press LLC.