Perceptual selection and the unconscious selection of ‘volunteer’ seedlings in clonally propagated crops: an example with African cassava (<Emphasis Type="Italic">Manihot esculenta</Emphasis> Crantz) using ethnobotany and population genetics

The role of sexual reproduction in magnifying genetic diversity in clonally propagated crops is now well documented. But whereas many studies have emphasized the importance of perceptual distinctiveness and its role in arousing farmers’ curiosity towards plants with unusual morphological traits, few have considered its corollary, perceptual indistinctiveness. In this study, we investigated which factors influence farmers’ behaviours towards self-sown ‘volunteer’ seedlings of cassava (Manihot esculenta Crantz) in a cross-cultural survey in Gabon, Central Africa. Interviews revealed that farmers were seven times more likely to spare seedlings that resembled a named landrace compared to those that did not. Similarly, farmers were more likely to relax weeding pressures on cassava volunteers if they believed that volunteers were resurgences from old cuttings. The model fit significantly improved when cultural factors were accounted for, suggesting strong culture-dependent differences among communities in their perception of and attitudes towards cassava volunteers. An analysis of the structure of genetic diversity of cassava landrace populations at the community level showed that most landraces included singleton genotypes, even in villages where farmers imposed the strongest weeding pressures, suggesting that there is always some background incorporation of cassava seedlings. We show that by channelling the selective incorporation of cassava seedlings that are morphologically indistinguishable from familiar landraces, perceptual selection favors the recruitment, sometimes deliberate but more often unconscious, of new genotypes from plants germinating from seeds and contributes to balancing the disadvantages of strictly clonal propagation, while maintaining landraces within consensual combinations of perceptually distinct traits.     

Inferring seed exchange between farmers from population genetic structure of barley landrace Arabi Aswad from Northern Syria

Apart from their significance in genetic conservation, barley landraces are still favoured by local farmers in low-input farming systems. They often perform more predictably under adverse conditions than modern cultivars due to local adaptation. Increased seed exchange between farmers may put adaptation of local populations of barley landraces at risk. Isozyme markers were used to investigate differentiation and infer gene flow between local populations of barley landrace Arabi Aswad in Northern Syria. Inferred gene flow decreased exponentially with geographic distance and may imply that seed exchange between farmers is limited to a regional scale and diminishes over longer distance. Gene flow seems to be a suitable index for estimating seed exchange in highly inbreeding crop species such as barley. In the future, improved mobility of farmers and extension work may facilitate seed exchange over longer distances, and consequently jeopardise preservation of locally adapted landraces in barley.     

Characterization of a flint maize (Zea mays L. convar. mays) Italian landrace: I. Morpho-phenological and agronomic traits

Maize (Zea mays L.) landraces have the highest genetic variation and adaptation to the natural and anthropological environment where they have evolved. Surveying both qualitative and quantitative morphological traits of existing landraces may be useful in maintaining their genetic diversity and preserving them from genetic erosion. Our research deals with the morpho-phenological and agronomic characterization of a flint maize landrace, named 'Nostrano di Storo', still grown in an inland hilly environment in the low valley of Chiese River in Trentino, North-Eastern Italy. The majority of plants from twenty field populations proved to belong, with few exceptions (NSt2, NSt9, NSt11), to a single population. It means that the plant material long grown in this area and maintained by local farmers through yearly selection forms a single landrace within which some populations (i.e. NSt1, NSt3, NSt4, NSt7, NSt10, NSt18, NSt19, NSt20) could be considered as most representative and taken as 'core'. This is supported by the fact that the genetic variability was much higher within than between field populations: half of the plant and ear traits investigated did not show any significant difference between populations whereas all traits but two showed highly significant differences within populations. Selection carried out over the years by each farmer according to his own criteria produced little genetic differentiation within the original population. Gene flow among farmer populations, most likely occurred through both pollen dispersion to neighboring cultivated fields and seed exchange among farmers, may help to explain the low genetic differentiation. This information is useful for both planning conservation and recognizing the landrace as a unique germplasm source of specific geographic origin.     

Complexity and adaptability of a traditional agricultural system: case study of a gall midge resistant rice landrace from northern Thailand

Adaptability of traditional agricultural systems is suggested by their success over time, but documentation of how this happens is rare. This paper shows how genetic diversity in a rice landrace enables rice farming system of northern Thailand to adapt to a constraint of an insect pest, microenvironments of mountainous landscape and people’s different tastes in rice. Resistance to laboratory-reared gall midge varied among accessions the rice landrace Muey Nawng and gall midge populations. Higher rice yield in farmers’ fields reflected adaptation to local environment as well as resistance to gall midge. Microsatellite variation of the accessions correlated negatively with their gall midge resistance, but there was also variation in heading time and endosperm starch. Presence of non-waxy endosperm in glutinous rice provides opportunity to select for rice that is cooked into non-glutinous rice preferred by minority groups who live at higher elevations, where the gall midge is emerging as a new threat, possibly because of climate change. These data show how genetic diversity of a rice landrace coupled with seed management by farmers enabled a rice farming system to adapt to the varied microenvironment of a mountainous landscape under the constraint of an insect pest and people’s different tastes in rice.     

Traditional Crop Diversity and its Conservation on-Farm for Sustainable Agricultural Production in Kumaon Himalaya of Uttaranchal State: A Case Study

Farming communities in traditional agroecosystems have been playing an important role in conserving agricultural diversity. They are not only the custodians but also managers of the crop diversity and maintain the dynamic processes of crop evolution and adaptation, the key elements of sustainable agricultural productions. The Himalayan highlands are important centres of crop plant diversity due to high ecological heterogeneity and high local socio-cultural integrations. The crop genetic diversity of Kumaon Himalaya in Uttarachal State of India has been documented in the present study. Existing crop genetic diversity at inter- and intra-species level was assessed and factors for changes in crop compositions and farming systems during the recent past were studied. Farmer management of rice landrace populations were studied in greater detail. Various benefit enhancing options for farmers from local crop diversity were scrutinized based on farmer perceptions and priorities for efficient management of local crop diversity on-farm and its sustainable utilization for agricultural production.     

Farmers' practices, metapopulation dynamics, and conservation of agricultural biodiversity on-farm: a case study of sorghum among the Duupa in sub-sahelian Cameroon

In many traditionally managed agroecosystems, populations of domesticated plants maintain high levels of genetic diversity. The threat of erosion of this diversity is a current conservation concern, motivating studies of how diversity can be maintained by in situ conservation measures. Precisely how the biological traits of plants and the cultural practices of farmers act on fundamental evolutionary forces - drift, migration, selection, and mutation - to create and maintain crop plant diversity has been little investigated in detail. We develop some elements of the framework required for studying such biocultural interactions, focusing on one component of management: farmers' decisions on what to plant, and the structure of germplasm exchange among farmers. We illustrate the approach with a study of Duupa farmers in northern Cameroon. Our results suggest that sorghum populations managed by the Duupa function like source-sink metapopulations. Fields of older farmers, larger and containing a greater number of varieties, act as sources, whereas fields of younger farmers act as sinks, becoming sources as their owners mature. In each field, seeds for sowing are selected from a small number of plants. The frequent exchange of germplasm among fields may counteract the genetic bottlenecks associated with the small number of genitors within each field. Identifying key processes and key individuals should facilitate the design of in situ conservation measures to maintain crop plant diversity against the threat of genetic erosion.     

Role of informal seed system in promoting landrace diversity and their on-farm conservation: a case study of rice in Indian Himalayas

Role of informal seed system in landrace diversification, in situ conservation on-farm and sustainability in production were investigated as a case study for rice diversity in Indian Himalayas. The diachronic pattern of landrace occurrence revealed substantial increase, both in landrace number and frequency, in time. The local level seed supply in Uttarakhand Himalaya revealed that about 96% seed supply originated from informal system and a mere 4% seed supply is met from formal seed supply networks. In higher elevation ranges, beyond 1200 masl, largely landrace cultivation is practiced and a greater landrace diversification in traditional production was observed. Substantial variations due to environmental adaptations in niche habitats help provide important donor germplasm for crop improvement to users. Further, the population genetic structure also indicated enough diversity being maintained on-farm. Developing pathways for strengthening local level seed system for landrace diversification linked to sustainability in food production and conserving agro-biodiversity has been emphasized.     

Ecological and genetic effects on demographic processes: pollination, clonality and seed production in Dithyrea maritima

The relative importance of ecological and genetic factors in regulating the demographic processes of small populations is unknown for most rare plants. Dithyrea maritima (beach spectacle pod; Brassicaceae) is a rare, rhizomatously spreading, and self-incompatible herbaceous perennial endemic to coastal sand dunes of southern California. Low seed production in this species may be caused by insufficient pollinator visits, which may be exacerbated by competition for pollinator visits from non-native plants that have invaded the coastal dunes. I tested this ‘ecological’ hypothesis by removing flowers of Cakile maritima and Carpobrotus spp. from three experimental plots on San Nicolas Island. A second possible limitation on seed set is low diversity of genets within subpopulations, which could lead to scarcity of compatible mates. I tested this ‘genetic’ hypothesis by assigning ramets to clones using isozymes, and by relating clonal diversity within populations to seed set. Removal of non-native plants had no detectable effect on pollination service to D. maritima or on seed set, and seed set was unrelated to natural variation in pollination service among populations within a single year. In contrast, clonal diversity within a 10 m² patch was a strong predictor of seed set. Hence a genetic factor explains spatial variation in seed set on San Nicolas Island. On larger spatial and temporal scales, however, pollination service also affects patterns of seed set: a shift in pollination from flies in 1998 to bees in 1999 probably caused a corresponding increase in seed set across San Nicolas Island, while extremely low seed set at another site (San Miguel Island) is probably caused by a virtual absence of pollinators there.     

Classification of elite cassava varieties (<Emphasis Type="Italic">Manihot esculenta</Emphasis> Crantz) cultivated in Benin Republic using farmers’ knowledge,morphological traits and simple sequence repeat (SSR) markers

Cassava (Manihot esculenta Crantz) is an important food security crop or resource for poor rural communities particularly in Africa. The crop’s ability to produce high yields even under poor conditions and storability of its roots underground for longer periods or until needed makes it a model ‘food security crop’. In Benin Republic, cassava has been recognized as one of the major crop contributing towards dynamic value chains generating incomes for small-holder farmers. The crop is grown all over the country, however, the increased production are mainly recorded from far south and central parts of the country. Genetic improvement of cassava in Benin Republic is limited because of poor knowledge of genetic diversity present within the country. The main objective of this study was to assess the genetic diversity and relationships among elite cassava varieties collected from different regions of Benin using fluorescently labelled simple sequence repeat (SSR) markers and to compare the results with farmer’s knowledge and morphological traits. A total of 96 cultivars collected from major cassava growing areas such as Southern and Central Benin were classified into 24 different groups using farmers’ knowledge, while classification based on 18 morphological traits resulted in five groups. In total, sixteen SSR markers were tested for molecular analysis of the ninety-six cassava varieties. Among the sixteen, twelve SSR markers gave good banding pattern and were used to genotype the varieties. An average of 3.58 and 0.47 for number of alleles and polymorphism information content respectively was observed. The observed heterozygosity (H_o) ranged from 0.23 to 1.0 with an average of 0.66 indicating moderate level of diversity among the cultivars. Based on the proportion of shared alleles and hierarchical clustering, the 96 elite cassava varieties were classified as 74 unique varieties. Principal component analysis and analysis of molecular variance revealed no significant variation between the regions thus, explaining regular exchange of planting materials among cassava farmers across various regions. The moderate level of genetic diversity in famer’s field, revealed in the present study, is a good indication of the need for broadening the genetic base of cassava in Benin Republic and establishing a formal breeding program in the country.     

Effect of farmers' seed selection on genetic variation of a landrace population of pepper (Capsicum annuum L.), grown in North-West Italy

Recognition by the European Community of élite landraces encourages farmers to grow these and earn more than is possible by growing modern varieties. However, farmers often exercise strong selection by collecting seed from a limited number of plants which best embody a few characters of prime interest. This, in the long run, may be responsible for considerable genetic erosion. In Southern Piedmont, North-West Italy, a local landrace of pepper (Capsicum annuum L.) known as Cuneo is grown; it deserves particular attention because of its hardiness, late production and fruit quality. We used random amplified polymorphic DNA (RAPD) and amplified fragment length polymorphism (AFLP) markers to assess the effect, on genetic composition of a population, of seed sampling carried out using the selection criteria adopted by the farmer. After two reproductive cycles using selection, it was already possible to detect loss in genetic variation and a change in allele frequencies, while no significant effect was found after two cycles of random sampling. Over this period, farmer selection pressure led to disappearance of eight low-frequency alleles, while only three alleles were lost in randomly sampled populations. Our results stress the need to adopt appropriate techniques for seed sampling in order to avoid genetic erosion of local landrace gene pools.     

Traditional seed management and genetic diversity in barley varieties in high-hill agro-ecosystems of Nepal

Chawali and Lekali are two common farmer’s barley varieties or landraces in Jumla, Nepal (2,240–3,000 m) with small to bold grains and wide adaptation from irrigated low lands to high hills. This study was undertaken to test whether features of the traditional seed system can significantly influence the diversity of a crop and its conservation on-farm. In Jumla (high-hill), the barley seed system is completely informal and is mainly from farmer to farmer. In the present study, the seed flows and the pattern of genetic diversity in barley were investigated to detect differences between the two varieties and test the divergence among populations of each variety These data suggested that Chawali, the more common variety, was less subject to homogenising gene flow between farms than was Lekali. A total of 128 farming households were surveyed for seed supply information and 128 populations for each landrace from two villages: Kartikswami and Talium were collected for SSR diversity analysis. Some 92 SSRs were screened in an initial sample of 20 barley populations of both landraces and 2 improved varieties (LG-51 and Soluwa). Of the 81 SSRs that consistently amplified, only 15 SSRs (19%) were polymorphic with gene diversity values ranging from 0.09 to 0.71. A medium to low diversity was detected among the landrace populations of barley varieties. Chawali populations were less polymorphic within ecological groups, and more divergent between than were Lekail populations. This result accords with Chawali having a more conservative local seed system.     

Social and environmental influences on tartary buckwheat (<Emphasis Type="Italic">Fagopyrum tataricum</Emphasis> Gaertn.) varietal diversity in Yunnan,China

Effective conservation strategies aimed to protect crop genetic resources require multiple sources of information. We used a combination of AFLP genotyping and farmer surveys to understand the extent, distribution and management of tartary buckwheat (Fagopyrum tataricum Gaertn.) diversity in its center of origin in Yunnan Province, China. We found genetic evidence of gene flow in tartary buckwheat throughout the study area, with small but statistically significant regional and village-level components. We also found genetic differentiation by seed color. Although most farmers reported exchanging seed in localized kinship networks, our results imply homogenizing gene flow is occurring. Yi ethnic farmers tend to plant more buckwheat than non-Yi farmers, and we found that in some communities, Yi farmers serve as seed sources for farmers of other ethnicities. Different tartary buckwheat varieties did not have different end uses; rather farmers maintained varietal diversity in order to protect crop yield and quality. Individual farmers’ seed exchange practices reflect their ideas about components of seed quality, as well as priorities in protecting buckwheat yield. From the standpoint of genetic resources conservation, the presence of a culturally rich farmer exchange network and hierarchical structuring of tartary buckwheat genetic diversity demonstrates the importance of maintaining an interlinked community of tartary buckwheat farmers in Yunnan.     

Toward the restoration of a sustainable population of a threatened aquatic plant, Nymphoides peltata: Integrated genetic/demographic studies and practices

We provide a brief review of practices and relevant studies for restoration of Nymphoides peltata (yellow floating heart, Asaza), a distylous floating-leaf clonal plant, in Lake Kasumigaura, Japan to develop a model of integrated genetic and demographic conservation for threatened plants. Several theoretically expected issues, such as sudden extinction of small populations with low genetic diversity, limited seed production in small-sized local populations, and significantly high heterozygosity in adults that have survived environmental change, were ascertained through integrated studies on demography with discrimination of genets and genetics using highly polymorphic genetic markers. Investigation of genetic properties of the remnant soil seed bank suggested that the seed bank could potentially restore genetic diversity, although the fitness reduction of seed banks caused by inbreeding could affect the success of restoration. As a result of restoration efforts, increases in the number of local populations and genets in the Lake Kasumigaura metapopulation have led to population recovery.     

Bambara groundnut (Vigna subterranea) seed quality in response to water stress on maternal plants

Farmers who still cultivate bambara groundnut (Vigna subterranea) rely on landraces and seed retained from previous harvests. Given that the crop is typically cultivated in semi-arid regions, seed quality of farmers' retained seed might be compromised due to water stress experienced by maternal plants during production. The aim of this study was to determine the effect of water stress on maternal plants on subsequent seed quality of bambara groundnut. A single bambara groundnut landrace was characterised into four distinct selections based on seed coat and speckling colour. Initial seed quality (viability and vigour) was evaluated prior to planting seed in a field trial under irrigated and rainfed conditions. Final yield and yield components were determined at harvest. Thereafter, seed quality (viability and vigour) of progeny of different landrace selections was evaluated. Yield was lower under rainfed than irrigated conditions. Overall, subsequent seed quality showed improvement from initial seed quality of the original seedlot. Seed viability was higher in seeds produced under irrigated than rainfed conditions. Seed quality of bambara groundnut may be reduced underwater-limited production conditions. Seed enhancement practices such as priming may assist farmers to achieve better emergence. In the long term, seed production should be done under optimum conditions in order to achieve high-seed quality.     

Molecular marker-mediated validation of morphologically defined landraces of Pejibaye (<Emphasis Type="Italic">Bactris gasipaes</Emphasis>) and their phylogenetic relationships

RAPD markers were used to evaluate the genetic variability and structure of seven morphologically defined landraces of pejibaye (Bactris gasipaes Kunth, Palmae) to determine their validity and phylogenetic relationships. Two hundred and twenty plants of four Amazonian and three Central American landraces of var.gasipaes (the domesticate) and 30 plants of var.chichagui (H. Karsten) Henderson (the crop ancestor) maintained at the National Research Institute for Amazonia, Manaus, Amazonas, Brazil, were utilized. Eight RAPD primers yielded 113 markers, with good reproducibility, of which 97 were polymorphic. The four Amazonian landraces had an average heterozygosity of 0.30, with 86% polymorphism, greater than the Central American landraces (0.25; 74.3%) and var.chichagui (0.27; 80%). Among landrace genetic diversity (G_ST) was 15%, while within (Hs) was 85%, essentially equivalent to the AMOVA within (82.2%) and among (17.8%) variances. The Jaccard similarities, PCA, gene flow coefficients and Exact tests suggested that only one landrace exists in Central America, called Utilis after the first taxon described there, and that the Solimões landrace is part of the Putumayo landrace, rather than a separate entity. The Pará and Pampa Hermosa landraces were validated in accordance with their morphometric interpretations. The dendrogram of Neis genetic distances among valid landraces and var.chichagui supported the hypothesis of a single origin for pejibaye in southwestern Amazonia, with two migration routes: one to the northeast, becoming the Pará landrace, and another to the northwest along the Andes, spreading into western Amazonia (Pampa Hermosa and Putumayo landraces) and across the Andes, reaching Central America (Utilis landrace).     

Genetic variation of the durum wheat landrace Haurani from different agro-ecological regions

The durum wheat landrace Haurani (Triticum durum Desf.) is grown under contrasting climatic regions of Syria from Deir Ezzor, in the North-East (230 m altitude, 150 mm mean annual rainfall), to Qunaytra, in the South-West (1060 m altitude, 825 mm mean annual rainfall). In order to assess the genetic variation between and within Haurani populations, samples from eight provinces of Syria (Daraa, Damascus, Qunaytra, Deir Ezzor, Hassakeh, Aleppo, Homs and Hama) were analysed by RFLPs and seed storage proteins of glutenin subunits as markers. The analyses showed the presence of genetic polymorphisms in all populations with the highest values in those from Homs and Hassakeh. Moreover, the results point out differences in genetic distances between populations; some populations were further apart, such as Damascus and Aleppo, whereas others were closer to each other, for instance Homs and Hama. Cluster analysis identified two distinct groups of populations, characterized by geographical proximity, with similar rainfall and altitude. It is suggested that the similarity of landraces at locations close to each other might be the result of more frequent seed exchanges between farmers or of gene flow due to 5% estimated outcross rate of Haurani.     

Distribution, species composition and management implications of seed banks in southern New England coastal plain ponds

Buried seeds that germinate during periods of low water or water level drawdown can play important roles in shaping plant community composition, community dynamics and species richness in ecosystems with fluctuating water levels. Northeastern US coastal plain ponds have fluctuating water levels and contain a characteristic shoreline flora that contains many rare plants. The objectives of this study were to: (1) test whether geographically distant ponds in Cape Cod and Martha’s Vineyard had distinct seed banks, (2) determine if hydrologic status as permanent and ephemeral ponds led to differences in seed banks, and (3) examine seed diversity and seed abundance across gradients of shoreline elevations and sediment characteristics. Viable seeds of 45 plant species were identified from nine ponds. Native species dominated pond-shore seed banks and made up 89-100% of all species. There was high overlap in seed bank composition across hydrological classes and geographic regions. One hydrological class captured 73-76% of total species and one geographical region captured 69-78% of the total species recovered from the entire suite of seed bank samples. Seeds were relatively evenly distributed along the shorelines of ephemeral ponds but seed diversity and abundance were lower at low elevations in permanent ponds. Results suggest that strategies to protect pond shorelines to capture maximum diversity of coastal plain pond plants contained in pond sediment seed banks should be implemented across pond hydrologic classes and across a wide geographic area. Shoreline seed distributions indicate that ground-water withdrawals or climate changes that lower pond water levels in permanent ponds will reduce the diversity and abundance of plants recovered from seed banks by shifting water levels to a shoreline zone of high sediment organic matter where seed densities are lower. This effect will be much less in ephemeral ponds where seed diversity and abundance on pond bottoms was high.     

Diversity in reproductive characteristics of potato landraces and cultivars for producing true seed

Potato production from true seed, or true potato seed (TPS) is not a new system for this vegetatively propagated crop. Andean farmers have grown potatoes in the cool highlands from true seed for many centuries. TPS appears today as a promising technology in the warm tropics, where diseases impede the production of pathogen-free potato propagules. However, the identification of suitable genetic resources for potato seed production requires the selection of clones that lack antagonism between tuber growth and seed embryo development. Furthermore, the potential TPS parents need to possess characteristics of a sexually propagated crop that is grown for the harvest of its vegetative part, i.e., the tuber. This new process of domestication requires a change in the selection methods, which starts by assessing the potential of available potato clones for both reproductive characteristics and agronomic traits, particularly those of the tuber. Tetraploid landraces and cultivars of the pathogen-tested collection of the Centro Internacional de la Papa were assessed for reproductive and agronomic characteristics during three consecutive years in San Ramón, a Peruvian location in the warm lowland tropics. The clones showed significant variation for all characteristics recorded. The Shannon–Weaver diversity index (H) was highest for flowering duration (0.617) and intensity (0.600). The lowest H was calculated for bee attraction in this location. The overall H was not significantly affected by the year-to-year variation, but some of the characteristics recorded (e.g. flowers per inflorescence, anther type, style length, plus fruit and berry set) showed distinct H according to the year of assessment. Some of the cultivars with promising TPS traits, as determined by their reproductive characteristics, also had outstanding tuber set, weight and yield. Furthermore, hybrid offspring from the selected clones from the pathogen-tested elite sample, did show high tuber yield with appropriate tuber set and reproductive traits as shown by progeny testing. Hence, the approach followed for identifying parental sources as discussed in this article appears to be appropriate.     

Genetic differentiation of watermelon landrace types in Mali revealed by microsatellite (SSR) markers

This study describes the genetic differentiation of a collection of 134 watermelon landrace accessions from Mali, representing red fleshed dessert and white fleshed seed and cooking type watermelons from five regions, plus three commercial dessert type cultivars with red flesh. The material was represented by in total 397 plants and was analysed using 24 microsatellite primer sets, which differentiated 129 alleles across all loci. Analyses of molecular variance ascribed 51 % of the variation among the landrace accessions, and 14 % of the variation could be ascribed to the regions. Partitioning the accessions into use groups (dessert, cooking, seed processing) explained 25 % of the variation. When categorising the accessions further into 10 landrace types, differentiated on the basis of use groups, local accession name, flesh colour and seed phenotype, these landrace types explained 26 % of the variation. Analysis with the software Structure revealed that the accessions with confidence could be separated into two major genetic groups, related to flesh colour (red and white) of the watermelon fruits. The same analysis further indicated that the material may be differentiated into eight genetic sub-groups. One group included again the red fleshed dessert types with local and commercial origin, while the remaining seven genetic sub-groups comprised the white fleshed landrace types used for seed processing and cooking, as well as white fleshed types of one dessert type. Some of the seed and cooking types were to a large extent different and assigned to one genetic sub-group each. A Mantel test, based on geographical and genetic distance matrices showed a positive correlation, indicating that seed exchange has not overcome local adaptation.     

Economic concepts for designing policies to conserve crop genetic resources on farms

The future food supply of all societies depends on the exploitation of genetic recombination and allelic diversity for crop improvement, and many of the world's farmers depend directly on the harvests of the genetic diversity they sow for food and fodder as well as the next season's seed. On farm conservation is an important component of the global strategy to conserve crop genetic resources, though the structure of costs and benefits from on farm conservation differ from those associated with ex situ conservation in gene banks. A fundamental problem that affects the design of policies to encourage on farm conservation is that crop genetic diversity is an impure public good, meaning that it has both private and public economic attributes. This concept is defined and made operational in order to assist practitioners in identifying (1) least-cost sites for on farm conservation (2) the types of policy instruments that might be appropriate for supporting conservation once a site has been located. Published findings regarding prospects for on farm conservation as economies develop are summarized and empirical examples of suitable policies to support farmers' decisions are placed in the context of economics principles.