Crop genetic erosion: understanding and responding to loss of crop diversity.

Crop diversity underpins the productivity, resilience and adaptive capacity of agriculture. Loss of this diversity, termed crop genetic erosion, is therefore concerning. While alarms regarding evident declines in crop diversity have been raised for over a century, the magnitude, trajectory, drivers and significance of these losses remain insufficiently understood. We outline the various definitions, measurements, scales and sources of information on crop genetic erosion. We then provide a synthesis of evidence regarding changes in the diversity of traditional crop landraces on farms, modern crop cultivars in agriculture, crop wild relatives in their natural habitats and crop genetic resources held in conservation repositories. This evidence indicates that marked losses, but also maintenance and increases in diversity, have occurred in all these contexts, the extent depending on species, taxonomic and geographic scale, and region, as well as analytical approach. We discuss steps needed to further advance knowledge around the agricultural and societal significance, as well as conservation implications, of crop genetic erosion. Finally, we propose actions to mitigate, stem and reverse further losses of crop diversity.

Advances in biocultural geography of olive tree (Olea europaea L.) landscapes by merging biological and historical assays.

Olive tree is a vector of cultural heritage in Mediterranean. This study explored the biocultural geography of extra virgin olive oil (EVOO) from the cultivar Ogliarola campana in Campania region, Italy. Here, the rich cultural elements related to olive tree and oil represent a suitable case study for a biocultural analysis. We joined analytical techniques, based on stable isotopes and trace elements of EVOOs, with humanistic analyses, based on toponymy and historical data. In order to provide a science-based assessment of the terroir concept, we set up a new method of data analysis that inputs heterogeneous data from analytical and anthropic variables and outputs an original global evaluation score, named terroir score, as a measure of biocultural distinctiveness of the production areas. The analysis highlighted two distinct cultural sub-regions in the production area of Ogliarola campana: a continental cluster in the inner area of Irpinia and a coastal one around Salerno province. Finally, a biocultural map displays the diversity of heterogeneous variables and may support science-based decision making for territory valorisation. This novel biocultural analysis is a promising approach to substantiate the terroir concept with science-based elements and appears suitable to characterize local agri-food products with old tradition and historical data.

Potato Diversity in the Andean Center of Crop Domestication.

The diversity and population structure of potato landraces (Solanum spp.) within their center of domestication was studied using isozyme surveys of four polymorphic loci. The objective in assessing the distribution of genetic diversity was to assist in planning conservation strategies of crop genetic resources that are threatened by genetic erosion. In situ conservation methods depend on this type of analysis. Research was conducted in the region of Cusco, Peru. Eight fields spread among two microregions were randomly sampled, and 610 tubers were studied from this sample. In addition, 503 tubers were collected from markets in seven different meso-regions (provinces) surrounding the regional center of Cusco. Thirty genotypes were identified in the field sample and 82 in the regional sample. The frequency and distribution of genotypes and alleles are described. A high degree of genotype endemism was found at both the field and regional levels. Genotypes were unevenly distributed, and most of the genotypic diversity was between rather than within populations. At the allele level, however, we found that a very high percentage of the diversity was within rather than between populations. The genotype is the key unit for maintaining the population of potato landraces. Our findings suggest that collections need to be both geographically extensive and intensive. Because farmers are able to maintain most alleles on relatively small portions of their land, in situ conservation is a viable strategy.

Resumen: La diversidad y estructura poblacional de razas locales de papa (Solanum spp.) en su centro de domesticación andino fué estudiado por medio de isoenzimas en cuatro loci polimórficos. La determinación de la distribución de la diversidad genética se hizo con el fin de ayudar en la planificación de las estrategias para la conservación de germoplasma en cultivos amenazados por la erosión genética, teniendo en cuenta que los métodos de conservación in situ dependen de este tipo de análisis. La investigación fue realizada en la región del Cusco, en Perú. Se muestrearon tubérculos al azar en ocho campos distribuidos en dos microregiones, haciendo un total de 610 tubérculos. Por otro lado, 503 tubérculos fueron colectados en los mercados de siete provincias alrededor de la cuidad del Cusco, Perú. Treinta genotipos fueron identificados en las colectas hechas en los campos de los campesinos y 82 en la colección de los mercados, sirviendo para describir la frequencia y distribución de genotipos y alelos en las dos colecciones. La distribución no fué uniforme, encontrándose la mayor parte de la diversidad entre poblaciones, indicando que el genotipo es la unidad clave en el mantenimiento de las razes locales de papas. Nuestro estudio sugiere que las colecciones de germoplasma de papas deben ser geográficamente amplias e intensas. La habilidad de los campensinos en mantener la mayoria de los alelos en sus pequeños terrenos indica que la conservación in situ es un estrategia viable. La diversidad de la papa en el centro andino de domesticacion de cultivos.

Maize diversity and ethnolinguistic diversity in Chiapas, Mexico.

The objective of this study is to investigate whether ethnolinguistic diversity influences crop diversity. Factors suggest a correlation between biological diversity of crops and cultural diversity. Although this correlation has been noted, little systematic research has focused on the role of culture in shaping crop diversity. This paper reports on research in the Maya highlands (altitude >1,800 m) of central Chiapas in southern Mexico that examined the distribution of maize (Zea mays) types among communities of two groups, the Tzeltal and Tzotzil. The findings suggest that maize populations are distinct according to ethnolinguistic group. However, a study of isozymes indicates no clear separation of the region's maize into two distinct populations based on ethnolinguistic origin. A reciprocal garden experiment shows that there is adaptation of maize to its environment but that Tzeltal maize sometimes out-yields Tzotzil maize in Tzotzil environments. Because of the proximity of the two groups and selection for yield, we would expect that the superior maize would dominate both groups' maize populations, but we find that such domination is not the case. The role of ethnolinguistic identity in shaping social networks and information exchange is discussed in relation to landrace differentiation.

How theories became knowledge: Morgan's chromosome theory of heredity in America and Britain.

T. H. Morgan, A. H. Sturtevant, H. J. Muller and C. B. Bridges published their comprehensive treatise The Mechanism of Mendelian Heredity in 1915. By 1920 Morgan's "Chromosome Theory of Heredity" was generally accepted by geneticists in the United States, and by British geneticists by 1925. By 1930 it had been incorporated into most general biology, botany, and zoology textbooks as established knowledge. In this paper, I examine the reasons why it was accepted as part of a series of comparative studies of theory-acceptance in the sciences. In this context it is of interest to look at the persuasiveness of confirmed novel predictions, a factor often regarded by philosophers of science as the most important way to justify a theory. Here it turns out to play a role in the decision of some geneticists to accept the theory, but is generally less important than the CTH's ability to explain Mendelian inheritance, sex-linked inheritance, non-disjunction, and the connection between linkage groups and the number of chromosome pairs; in other words, to establish a firm connection between genetics and cytology. It is remarkable that geneticists were willing to accept the CTH as applicable to all organisms at a time when it had been confirmed only for Drosophila. The construction of maps showing the location on the chromosomes of genes for specific characters was especially convincing for non-geneticists.