Stephen B. Brush

Genes in the field : on-farm conservation of crop diversity

Introduction and Overview * The issues of in situ conservation of crop genetic resources * Population Biology and Social Science: The Genetic Structure of Crop Landraces and the Challenge to Conserve Them in situ on Farms - Case Studies * Barley Landraces From the Fertile Crescent: a lesson for Plant Breeders * The Barleys of Ethiopia. Traditional Management of Seed and Genetic Diversity: What is a Landrace?- Keeping Diversity Alive: an Ethiopian Perspective * Policy and Institutional Issues: Optimal Genetic Resource Conservation: in situ and ex situ * The Cultures of the Seed in the Peruvian Andes * On-Farm Conservation of Crop Diversity: Policy and Institutional Lessons From Southern Africa * In Situ Conservation and Intellectual Property Rights * Farmer Decision-Making and Genetic Diversity: Linking Multidiciplinary Research to Implementation On-Farm.

Technology adoption and biological diversity in Andean potato agriculture

Abstract Biological diversity in cradle areas of crop origins has been an important source of genetic resources for world agriculture. The loss of biological resources in agricultural systems due to the introduction of high-yielding varieties is a potential cost of agricultural development. Our econometric analysis using data from Peru indicates that the adoption of high-yielding potato varieties results in a reduction but not a complete loss of biological diversity on individual farms and a possible loss in aggregate diversity. We conclude that on-site conservation of seed resources may be a viable complement to the off-site methods now in place.

Keepers of maize in Chiapas, Mexico

This study concerns the knowledge and selection of biological diversity of maize (Zea mays) within its center of domestication in Mesoamerica. Maize farmers in central Chiapas of Southern México keep local varieties (landraces) belonging to six races and four race mixtures. Fifteen local varieties are recognized. In spite of widespread adoption of a modern, high yielding variety, maize farmers continue to select local varieties for specific soils and because of agronomic and use criteria. Farmers maintain maize varieties primarily through seed selection. Spatial and temporal separation do not seem sufficient to maintain varieties. The management of improved varieties can lead from a uniform population to a heterogeneous one as hybridization with local maize populations occurs.AbstractEste estudio trata sobre el conocimiento y la selectión de la diversidad bioldgica de maíz (Zea mays) en su centro de domesticatión en Mesoamerica. Pequeños productores de maíz en la parte central del Estado de Chiapas en el sureste de México mantienen variedades pertenecientes a seis razas y cuatro mezclas raciales. Se reconocen quince variedades locales. A pesar de la adoption de variedades mejoradas de alto rendimiento, estos agricultores continúan seleccionando variedades locales para suelos particulares y debido a criterios agronómicos y de uso. Estos agricultores mantienen sus variedades de maíz através the la selectión de la semilla. La separatión espacial y temporal no parecen ser suficientes para mantener estas variedades. El manejo de las variedades mejoradas puede conducir de una población uniforme a una heterogénea en la medida que occurre una hibridazación con las poblaciones locales de maíz.

A Farmer-based approach to conserving crop germplasm

In situ conservation of crop genetic resources from centers of agricultural diversity is considered. This strategy has been rejected for several reasons, but other factors make it an important potential contributor to the overall conservation effort. Case studies of potato agriculture in Peru, maize agriculture in Mexico, and rice agriculture in Thailand indicate that farmers frequently engage in de facto conservation of landraces. Five principles should guide planning of in situ conservation: complementarity with off-site conservation, minimal institutional development, continuity with existing programs, meeting the development goals of increasing income and food, and accepting germplasm as an international public good. Four means to implement on-site conservation are presented: the institutional framework; the information base; the policy framework; and the role of grassroots organizations.

Landraces of Maize in Central Mexico: An Altitudinal Transect

Conservation of crop genetic resources is now considered an important component of sustainable agricultural development. If conservation of genetic resources for agriculture is to be successful, a more complete understanding of the dynamics affecting traditional (landrace) crop populations is needed. We conducted a study of maize-based agriculture in the Central Highlands of Mexico in communities at 2400, 1700, 1400, and 1200 masl to assess the status of traditional varieties in an area characterized by thorough integration into the national economy. Our research contradicts the view that modern varieties persist because of marginal conditions, deficient infrastructure, weaker markets, or traditional attitudes. One or two landraces dominated highland maize populations and farmers appeared to be more conservative in terms of their emphasis on traditional maize varieties than at lower elevations. The dominance of traditional varieties in the highlands is well known but poorly explained, and the coexistence of traditional and modern varieties in the mid-elevations was unexpected. Our highland study area has good roads, is near Mexico City, and is less than 50 km away from four major crop research institutes that have done maize breeding since 1950’s. We suggest that in situ conservation of maize genetic resources in the highlands is sustained because the landraces there have good agronomic performance and are highly valued by farmers for their end-use qualities. At the mid-elevations, competition between local and modern maize was sharpest, and farmers have found that both landraces and improved varieties suit their needs, hence enhancing genetic diversity. Interventions and incentives would appropriately be carried out here to assure in situ conservation of locally adapted landraces of maize.

Dynamic Management of Maize Landraces in Central Mexico

Conservationists of crop genetic resources have feared that in situ conservation was not viable for agriculture precisely because of changes resulting from introduction of new varieties of existing crops, new crops, and new farm practices. In addition, conservation within farming systems necessarily implies a constantly changing crop population resulting from the processes of crop evolution. Even though in situ conservation of crop genetic resources is now generally understood to be dynamic, there are few examples of how evolution takes place in farmers fields. This study describes several changes in maize landraces in four communities along an altitude transect in Central Mexico (1200 to 2400 masl). While true modern varieties have not been widely adopted in the study region, farmer management results in numerous changes in maize landrace populations. Five types of dynamic management were observed: (1) purposeful hybridization between traditional and modern maize types, (2) possible creation of a new maize landrace by directional selection of the progeny of hybridization between two traditional landraces, (3) displacement of a local landrace by the introduction of a modern variety and a non-local landrace, (4) maintenance of stable populations of a locally dominant landrace, and (5) market-driven selection for a minor variety. We concur that in situ conservation of crops must be conceived as an open process where the objective is not to maintain historic varieties or static genetic conditions. Rather, in situ conservation of crops is totally in the hands of the farmer, although interventions may be designed to influence farmers’ management of agrobiodiversity.

Biochemical and folk assessment of variability of Andean cultivated potatoes

Isozyme markers were used to survey the genetic variability of non-bitter potatoes in 10 subsistence fields of Andean farmers at 3600-3850 m above sea level. Sixty-seven percent of the varieties were tetraploids corresponding to the speciesSolanum tuberosum ssp.andigena, 14% were triploids, probably corresponding to the speciesS. x chaucha, and 13% were diploids corresponding to the speciesS. stenotomum, S. phureja, andS. goniocalyx. The isozyme information served to determine the consistency of the folk naming system. We found a high degree of correspondence between farmer identification and electrophoretic phenotypes. The consistency of the folk system in electrophoretic terms depended on the farmer who was interviewed. The most common incongruity consisted of calling different electrophoretic phenotypes by the same variety name, leading to a slight underestimation of genetic variability present in the fields. The amount of variability observed in the sample of the Andean potato population was superior to that present in North American and European varieties. This was measured in terms of number ofalleles, number of electrophoretic phenotypes and percent of heterozygosity. This finding supports the impression that a substantial amount of yet unexploited variability remains in Andean potato populations.ResumenEn este trabajo se da a conocer los resultados de un estudio genético sobre variedades de papa dulce en los Andes, realizada por medio de marcadores isoenzimáticos en parcelas de subsistencia localizados entre 3600 y 3850 metros sobre el nivel del mar. Se encontró que 67% de las variedades muestreadas eran tetraploides de la especie S. tuberosum ssp. andigena, 14% triploides probablemente de la especie S. x chaucha, y 13% diploides de las especiesS. stenotomum, S. phureja andS. goniocalyx. La información isoenzimática fue útil en la evaluatión de la precisión del sistema folklorico para identificar variedades. Se encontró un alto grado de asociación entre el sistema de clasificación usado por el campesino para denominar sus variedades, y los fenotipos electroforéticos. La precisión del sistema de identidad folklorico en tℰminos electroforéticos dependió del campesino entrevistado. La discrepancia mas frecuente entre los dos sistemas de nomenclatura consistió en llamar diferentes fenotipos electroforéticos con el mismo nombre varietal, lo que resultó en una subestimación de la variabilidad genética presente en los campos. El nivel de variabilidad observado en la muestra de papas de la población andina fue superior al observado en variedades nortea-mericanas y europeas. La variabilidad se midió en base al número de alelos, número de fenotipos electroforéticos y porcentaje de heterocigosidad. Estos resultados están de acuerdo con la impresión general de que todavía existe mucha variabilidad en variedades de papa andinas que no ha sido aún explotada.

Man's use of an andean ecosystem

The Andes are characterized by valley systems that differ according to the steepness of the environmental gradient as well as the human occupation and land use patterns. This article discusses the natural and crop zonation in one valley of the eastern Andes of northern Peru which includes many of the principal plant and crop zones of the Peruvian Andes. The entire valley is exploited by one peasant community. The article describes some of the land use patterns of the community and compares this valley system with others on the eastern slopes of the Andes.

Factors affecting adoption of hedgerows and other biodiversity-enhancing features on farms in California, USA

Although hedgerows, windbreaks, and other biodiversity-enhancing farm edge features offer the potential for ecosystem benefits without occupying much crop space, relatively few farms in California, USA include such features. Our study identified the practices currently used to manage non-cropped edges of fields, ponds, and watercourses in a case study area in California. We also identified social, economic, and agronomic incentives and constraints to installing biodiversity-enhancing edge features. More than one-third of the study farmers had installed native hedgerows, windbreaks, and/or grassed edges. Interviews demonstrated the importance of socially influential farmers working in tandem with public and private agencies to build initial interest in these practices. However, these features occupied less than four percent of all possible edge length. Constraints to increasing adoption included high costs, fear of harbouring weeds and rodents, and lack of certainty about ecosystems benefits, highlighting the need for cost-share programs and more regionally-focused agroecological research.

Reconsidering the green revolution: Diversity and stability in cradle areas of crop domestication

This paper reconsiders two widely held hypotheses about the effects of the green revolution, that it led to biological simplification and instability. The hypothesis of biological simplification (genetic erosion) is tested with evidence from Andean agriculture, where farmers maintain a significant degree of crop diversity even as they adopt modern crop varieties. The hypothesis of increased instability is tested with evidence from Asia where wheat and rice yields show no general pattern of increased instability. Neither of these hypotheses is confirmed. The conventional wisdom about the green revolution should be reconsidered with emphasis on resilience and variation in modernizing farming systems.