The activated torsion oscillation magnetometer

The activated torsion oscillation magnetometer exploits the mechanical resonance of a cantilever beam, driven by the torque exerted on the sample by an ac field applied perpendicularly to the film plane. We describe a model for the cantilever dynamics which leads to the calculation of the cantilever dynamic profile and allows the mechanical sensitivity of the instrument to be expressed in terms of the minimum electronically detectable displacement. We have developed a capacitance detector of small oscillations which is able to detect displacements of the order of 0.1 nm. We show that sensitivities of the order of 0.5(10-11 Am2 can be in principle achieved. We will subsequently describe the main features of the ATOM prototype which we have built and tested, with particular attention to the design solutions which have been adopted in order to reduce the effects of parasitic vibrations due either to acoustic noise, originating from the ac field coil, or to eddy currents in the capacitor electrodes. The instrument is mounted in a continuous flow cryostat and can work in the 4.2-300 K temperature range. Finally, we will show that our experimental set-up has a second mode of operation, named Torsion Induction Magnetometer (TIM).Comment: Invited Talk at the Moscow International Symposium on Magnetism, 2002 to appear in the J. Mag. Mag. Mat Revised versio

Taxonomic-linguistic study of plantain in Africa

Plantain is a cooking banana (Musa spp. AAB group (Musaceae)) that is grown as a major food crop in many parts of Africa, especially in the Central-African and West-African rain forest areas. The crop originated in Asia, but its greatest diversity is to be found in Africa.We are dealing here with an interspecific, triploid hybrid of Musa balbisiana and one or more sub-species of M. acuminata, with the genome formula AAB. The plant is sterile and can only be multiplied clonally, which is why breeding is difficult. Knowledge about the genetic background of the crop, however, is very important because once the parental sub-species are identified, these can be used in breeding.There are still many gaps in our knowledge about the history of plantain, both in Asia and in Africa. It is only fragmentarily known how, where and when the plant came into existence, when, whence and by whom it was brought to Africa and how it spread and diversified in this continent.Musa plants do not leave archaeological traces behind and historical sources are scarce. We only have present-day material at our disposal, i.e. cultivars and vernacular names, the nature, distribution and spread of which may give us clues about the history of the crop in the African continent.In doing so, we have to take into account other plants that are closely related to musa, or that have similar morphological features and/or uses, and therefore possess similar names in African languages. We also have to take into account the ecological conditions in those parts of the continent where plantain is grown, as well as the economies and (cultural) histories of the people cultivating plantain.A more technical problem is formed by the classification and nomenclature of plantain cultivars. Until now this problem has not been satisfactorily solved, and suggestions to this end are therefore presented in this study.This study is also meant to be an exploration into the possibilities of a multi-disciplinary approach to crop history. Ultimately, a better understanding of the historical background of crops might serve other disciplines too; in the first place, but not uniquely, plant breeding, plant taxonomy, ((agri)cultural) history and ethnobotany.</p

Are you really my clone? Identity verification of the in-trust sweetpotato collection at the International Potato Center.

The global in-trust sweetpotato collection maintained by the International Potato Center (CIP) in Lima, Peru consists of over 5,000 cultivated sweetpotato accessions maintained as clones in vitro as well as over 1,000 accessions from 67 species of Ipomoea maintained as seed populations. The clonal sweetpotato collection at CIP was initiated in the 1980’s and for 60% of the collection, original material still exists as potted plants in the greenhouse. This provides a unique opportunity where genetic integrity of a clonal collection, maintained in vitro for the past thirty years, can be confirmed by a side-by-side comparison of the same accession from the greenhouse. Initial molecular comparison is done using a set of twenty SSR primers followed by side-by-side comparison in the field using 30 morphological descriptors. Confirmation of identity requires both genetic and morphological analysis as a low percentage of the accessions appear to be duplicates based on SSR yet are morphologically distinct. Historical morphological descriptor data is used as a check to confirm identity and is being used as the sole check for accessions where we do not have original material for comparison. SSR results from 70% of the collection has confirmed that 85% of the in vitro accessions are true-to-type. In vitro accessions which are not true-to-type are reisolated and cleaned of viruses from the confirmed true-to-type greenhouse accessions. Accessions which are true-to-type are fingerprinted using DArTseq to provide a sequence-based fingerprint

Population genomics of the maize pathogen Ustilago maydis: demographic history and role of virulence clusters in adaptation

The tight interaction between pathogens and their hosts results in reciprocal selective forces that impact the genetic diversity of the interacting species. The footprints of this selection differ between pathosystems because of distinct life-history traits, demographic histories, or genome architectures. Here, we studied the genome-wide patterns of genetic diversity of 22 isolates of the causative agent of the corn smut disease, Ustilago maydis, originating from five locations in Mexico, the presumed center of origin of this species. In this species, many genes encoding secreted effector proteins reside in so-called virulence clusters in the genome, an arrangement that is so far not found in other filamentous plant pathogens. Using a combination of population genomic statistical analyses, we assessed the geographical, historical, and genome-wide variation of genetic diversity in this fungal pathogen. We report evidence of two partially admixed subpopulations that are only loosely associated with geographic origin. Using the multiple sequentially Markov coalescent model, we inferred the demographic history of the two pathogen subpopulations over the last 0.5 Myr. We show that both populations experienced a recent strong bottleneck starting around 10,000years ago, coinciding with the assumed time of maize domestication. Although the genome average genetic diversity is low compared with other fungal pathogens, we estimated that the rate of nonsynonymous adaptive substitutions is three times higher in genes located within virulence clusters compared with nonclustered genes, including nonclustered effector genes. These results highlight the role that these singular genomic regions play in the evolution of this pathogen

Desarrollo y aplicacion de PCR multiple para la deteccion simultanea de tres virus de ADN en camote (Ipomoea batatas L.)

El virus colusivo del camote (SPCV, genero Cavemovirus), el virus del aclaramiento de venas del camote (SPVC, genero Solendovirus) y el virus del enrollamiento de hojas del camote (SPLCV, genero Begomovirus) son virus con genoma de ADN, presentes en el camote en infecciones virales simples o multliples. La identificacion y deteccion de estos virus es complicada, ya que con frecuencia son asintomaticos y estan en concentraciones bajas en las plantas de camote. Se desarrollo una PCR multiple (mPCR) con el objetivo de lograr la deteccion simultanea de SPVC, SPVCV y SPLCV (y Begomovirus relacionados); para ellos se seleccionaron cebadores especificos para SPCV y SPVCV, y se utilizaron cebadores degenerados para Begomovirus (desarrollados por Li et al. 2004). Para la optimizacion de parametros se usaron plantas de camote con infecciones simples y mixtas. Se optimizo la concentracion de cebadores (0,1-0, 3uM), MgCl2 (2,5-8,0mM), dNTPs (0.2-0.8 mM), Taq-polimerasa (2-4U), parametros en el termociclador (temperatura de hibridacion de 48-62 oC y el numero de ciclos de 29-35), y la cantidad de acidos nucleidos (50-300 ng). Para validar le mPCR se uso plantas de camote de una coleccion de germplasma in vitro que estaban infectados con los virus en estudio y fueron confirmados por clonacion y secuenciamiento de las amplificaciones obtenidas. Los pares de cebadores especificos seleccionados para cada virus pudieron amplificar fragmentos de ADN en tamanos esperados, a una concentracion final de 0.16 uM para cebadores de SPCV y SPVCV, y 0.2uM para SPLCV. Ademas la concentracion de ADN adecuada esta entre 50-100 ng, con 30 ciclos termicos y 53 oC de temperatura de hibridacion. Este ensayo demostro ser simple, sensible y confiable para el diagnostico de rutina de SPCV, SPVCV y SPLCV (y Begomovirus relacionados). El ensayo de mPCR sera util para programas de cuarentena, como un metodos rapido y rentable para un gran numero de muestras