Detection of geminiviruses from tropical countries by a double monoclonal antibody ELISA using antibodies to African cassava mosaic virus

Using double antibody sandwich enzyme-linked immunosorbent assay (DAS-ELISA) tests, monoclonal antibodies (mAbs), which were prepared against particles of a Nigerian isolate of African cassava mosaic virus (ACMV), differentiated African geminiviruses (tomato yellow leaf curl virus, TYLCV; ACMV from West and East Africa; and okra leaf curl virus) from those originating in other countries of the world (euphorbia mosaic virus; Indian cassava mosaic virus; and TYLCV (Indian isolate)). All these viruses belong to the whitefly-transmitted geminivirus subgroup III. One mAb reacted with all 7 tested viruses and isolates. For detecting TYLCV from Senegal, it proved necessary to use a reducing agent in extraction buffer. A diagnostic DAS-ELISA was developed. This relies only on the use of mAbs and is useful for large-scale field screening.Des anticorps monoclonaux (AcMc) dirigés contre le virus de la mosaïque africaine du manioc («ACMV») (isolat du Nigéria) et utilisés dans un test DAS-ELISA («double antibody sandwich-ELISA») permettent de distinguer (à l’intérieur du sous-groupe III des geminivirus), les geminivirus originaires dAfrique (ACMV souche Ouest et Est ; virus de l’enroulement jaunissant de la tomate : «TYLCV» ; virus de l’enroulement du gombo) de ceux provenant des autres continents du monde (virus de la mosaïque de l’euphorbe ; virus indien de la mosaïque du manioc ; TYLCV de l’Inde). L’un de ces AcMc réagit avec les 7 geminivirus testés. Néanmoins, la détection du TYLCV (isolat du Sénégal) nécessite un tampon d’extraction spécifique, contenant un agent réducteur. Un test de diagnostic ou de détection utilisant seulement des AcMc, et par conséquent applicable à grande échelle, a été mis au point

Correlation between soil erodibility and satellite data on areas of current desertification: a case study in Senegal.

The purpose of the study is to verify whether some correlation exists between soil erodibility (i.e. K factor mentioned in RUSLE model) and data obtained from satellite images. This piece of work represents a first attempt towards a model that would predict the risk for soil erosion, from information contained in satellite images. Ouarchoch is a rural community in Ferlo Region, Senegal. It lies in a Sahelian typical arid zone and is affected by desertification processes. Ouarchoch site was the pilot area on which the test was performed. K factor was calculated by using soil textural data (sand, silt and clay) in the top (0 ? 5 cm) soil layer (data obtained from the web). Landsat7 satellite images represented different seasonal snapshots (?cool? dry season, warm dry season, rainy season, end of rainy season or beginning of dry season) of the same year, 2014. Calculation used Bands 1 to 7 and Normalized Difference Vegetation Index (NDVI). The choice of data, calculation and analysis are detailed. Some positive moderate correlation exists between soil erodibility on the one hand, and NDVI index displayed during the dry season (images in January and May), as well as Band 5 radiations displayed at the beginning of the dry season (post-harvest, image in October) on the other hand

Clustering of magnetic reconnection exhausts in the solar wind: An automated detection study

Context. Magnetic reconnection is a fundamental process in astrophysical plasmas that enables the dissipation of magnetic energy at kinetic scales. Detecting this process in situ is therefore key to furthering our understanding of energy conversion in space plasmas. However, reconnection jets typically scale from seconds to minutes in situ, and as such, finding them in the decades of data provided by solar wind missions since the beginning of the space era is an onerous task. Aims. In this work, we present a new approach for automatically identifying reconnection exhausts in situ in the solar wind. We apply the algorithm to Solar Orbiter data obtained while the spacecraft was positioned at between 0.6 and 0.8 AU and perform a statistical study on the jets we detect. Methods. The method for automatic detection is inspired by the visual identification process and strongly relies on the Walén relation. It is enhanced through the use of Bayesian inference and physical considerations to detect reconnection jets with a consistent approach. Results. Applying the detection algorithm to one month of Solar Orbiter data near 0.7 AU, we find an occurrence rate of seven jets per day, which is significantly higher than in previous studies performed at 1 AU. We show that they tend to cluster in the solar wind and are less likely to occur in the tenuous solar wind (< 10 cm−3 near 0.7 AU). We discuss why the source and the degree of Alfvénicity of the solar wind might have an impact on magnetic reconnection occurrence. Conclusions. By providing a tool to quickly identify potential magnetic reconnection exhausts in situ, we pave the way for broader statistical studies on magnetic reconnection in diverse plasma environments

Magnetic increases with central current sheets: Observations with Parker Solar Probe

Aims. We report the observation by Parker Solar Probe (PSP) of magnetic structures in the solar wind that present a strong peak in their magnetic field magnitude with an embedded central current sheet. Similar structures have been observed, either at the Earth’s magnetopause and called interlinked flux tubes, or in the solar wind and called interplanetary field enhancements. Methods. In this work, we first investigate two striking events in detail; one occurred in the regular slow solar wind on November 2, 2018 and the other was observed during a heliospheric current sheet crossing on November 13, 2018. They both show the presence of a central current sheet with a visible ion jet and general characteristics consistent with the occurrence of magnetic reconnection. We then performed a survey of PSP data from encounters 1 to 4 and find 18 additional events presenting an increase in the magnetic field magnitude of over 30% and a central current sheet. We performed a statistical study on the 20 "magnetic increases with central current sheet" (MICCS), with 13 observed in the regular slow solar wind with a constant polarity (i.e., identical strahl direction), and 7 which were specifically observed near a heliospheric current sheet (HCS) crossing. Results. We analyze and discuss the general properties of the structures, including the duration, location, amplitude, and magnetic topology, as well as the characteristics of their central current sheet. We find that the latter has a preferential orientation in the TN plane of the RTN frame. We also find no significant change in the dust impact rate in the vicinity of the MICCS under study, leading us to conclude that dust probably plays no role in the MICCS formation and evolution. Our findings are overall consistent with a double flux tube-configuration that would result from initially distinct flux tubes which interact during solar wind propagation

Solar Orbiter observations of the Kelvin-Helmholtz waves in the solar wind

Context. The Kelvin-HeImholtz (KH) instability is a nonlinear shear-driven instability that develops at the interface between shear flows in plasmas. KH waves have been inferred in various astrophysical plasmas, and have been observed in situ at the magnetospheric boundaries of solar-system planets and through remote sensing at the boundaries of coronal mass ejections. // Aims. KH waves are also expected to develop at flow shear interfaces in the solar wind. While they were hypothesized to play an important role in the mixing of plasmas and in triggering solar wind fluctuations, their direct and unambiguous observation in the solar wind was still lacking. // Methods. We report in-situ observations of quasi-periodic magnetic and velocity field variations plausibly associated with KH waves using Solar Orbiter during its cruise phase. They are found in a shear layer in the slow solar wind in the close vicinity of the Heliospheric Current Sheet. Analysis is performed to derive the local configuration of the waves. A 2-D MHD simulation is also set up with approximate empirical values to test the stability of the shear layer. In addition, magnetic spectra of the event are analyzed. Results. We find that the observed conditions satisfy the KH instability onset criterion from the linear theory analysis, and its de- velopment is further confirmed by the simulation. The current sheet geometry analyses are found to be consistent with KH wave development, albeit with some limitations likely owing to the complex 3D nature of the event and solar wind propagation. Addition- ally, we report observations of an ion jet consistent with magnetic reconnection at a compressed current sheet within the KH wave interval. The KH activity is found to excite magnetic and velocity fluctuations with power law scalings that approximately follow k−5/3 and k−2.8 in the inertial and dissipation ranges, respectively. Finally, we discuss reasons for the lack of in-situ KH wave detection in past data. // Conclusions. These observations provide robust evidence of KH wave development in the solar wind. This sheds new light on the process of shear-driven turbulence as mediated by the KH waves with implications for the driving of solar wind fluctuations

Historical Contingencies Modulate the Adaptability of Rice Yellow Mottle Virus

The rymv1-2 and rymv1-3 alleles of the RYMV1 resistance to Rice yellow mottle virus (RYMV), coded by an eIF(iso)4G1 gene, occur in a few cultivars of the Asiatic (Oryza sativa) and African (O. glaberrima) rice species, respectively. The most salient feature of the resistance breaking (RB) process is the converse genetic barrier to rymv1-2 and rymv1-3 resistance breakdown. This specificity is modulated by the amino acid (glutamic acid vs. threonine) at codon 49 of the Viral Protein genome-linked (VPg), a position which is adjacent to the virulence codons 48 and 52. Isolates with a glutamic acid (E) do not overcome rymv1-3 whereas those with a threonine (T) rarely overcome rymv1-2. We found that isolates with T49 had a strong selective advantage over isolates with E49 in O. glaberrima susceptible cultivars. This explains the fixation of the mutation T49 during RYMV evolution and accounts for the diversifying selection estimated at codon 49. Better adapted to O. glaberrima, isolates with T49 are also more prone than isolates with E49 to fix rymv1-3 RB mutations at codon 52 in resistant O. glaberrima cultivars. However, subsequent genetic constraints impaired the ability of isolates with T49 to fix rymv1-2 RB mutations at codons 48 and 52 in resistant O. sativa cultivars. The origin and role of the amino acid at codon 49 of the VPg exemplifies the importance of historical contingencies in the ability of RYMV to overcome RYMV1 resistance

Flux rope and dynamics of the heliospheric current sheet Study of the Parker Solar Probe and Solar Orbiter conjunction of June 2020

Context: Solar Orbiter and Parker Solar Probe jointly observed the solar wind for the first time in June 2020, capturing data from very different solar wind streams: calm, Alfvénic wind and also highly dynamic large-scale structures. Context. Our aim is to understand the origin and characteristics of the highly dynamic solar wind observed by the two probes, particularly in the vicinity of the heliospheric current sheet (HCS). Methods: We analyzed the plasma data obtained by Parker Solar Probe and Solar Orbiter in situ during the month of June 2020. We used the Alfvén-wave turbulence magnetohydrodynamic solar wind model WindPredict-AW and we performed two 3D simulations based on ADAPT solar magnetograms for this period. Results: We show that the dynamic regions measured by both spacecraft are pervaded by flux ropes close to the HCS. These flux ropes are also present in the simulations, forming at the tip of helmet streamers, that is, at the base of the heliospheric current sheet. The formation mechanism involves a pressure-driven instability followed by a fast tearing reconnection process. We further characterize the 3D spatial structure of helmet streamer born flux ropes, which appears in the simulations to be related to the network of quasi-separatrices

Magnetic reconnection as a mechanism to produce multiple protonpopulations and beams locally in the solar wind

Context. Spacecraft observations early revealed frequent multiple proton populations in the solar wind. Decades of research on their origin have focused on processes such as magnetic reconnection in the low corona and wave-particle interactions in the corona and locally in the solar wind.Aims.This study aims to highlight that multiple proton populations and beams are also produced by magnetic reconnection occurring locally in the solar wind. Methods. We use high resolution Solar Orbiter proton velocity distribution function measurements, complemented by electron and magnetic field data, to analyze the association of multiple proton populations and beams with magnetic reconnection during a period of slow Alfv\'enic solar wind on 16 July 2020. Results. At least 6 reconnecting current sheets with associated multiple proton populations and beams, including a case of magnetic reconnection at a switchback boundary, are found during this day. This represents 2% of the measured distribution functions. We discuss how this proportion may be underestimated, and how it may depend on solar wind type and distance from the Sun. Conclusions. Although suggesting a likely small contribution, but which remains to be quantitatively assessed, Solar Orbiter observations show that magnetic reconnection must be considered as one of the mechanisms that produce multiple proton populations and beams locally in the solar wind

Atelier ORIXAS: Projeto Tripartite África/Brasil/França: luta contra a desertificação: promoção da segurança alimentar e redução da pobreza.

No âmbito do Programa de Cooperação Científica Tripartite entre a Agence Inter-établissements de Recherche pourle Développement (AIRD), Agence Panafricaine de la Grande Muraille Verte (APGMV) e o Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq), o projeto ORIXAS "Observatórios Regionais Integrados de Regiões Árida, Semiáridas e Sub-úmidas secas" concebido em uma visão transversal, foca principalmente em metodologias e ferramentas para apoiar dispositivos de monitoramento ambiental para ser aplicado nos países inseridos na iniciativa africana Grande Muralha Verde - GMV (Burkina-Faso, Djibouti, Érythrée, Éthiopie, Mali, Mauritanie, Niger, Nigeria, Sénégal, Soudan, Tchad) e tem como objetivo desenvolver abordagens metodológicas e produtos compartilhados para melhorar a avaliação e monitoramento da desertificação e os impactos diretos ou indiretos de iniciativas para lutar contra o desmatamento e desertificação no âmbito da GMV. Esta publicação contempla aspectos metodológicos utilizados pelo projeto "ORIXAS" durante a primeira oficina de trabalho coletivo África-Brasil-França - Atelier (MAISON DE LA TÉLÉDÉTECTION), realizada de 10 a 19 de junho de 2014, em Montpellier França, objetivando informar a forma de execução dos estudos que vêm sendo realizados no escopo do projeto, visando principalmente a luta contra a desertificação, promoção da segurança alimentar e redução da pobreza nos países inseridos na iniciativa africana Grande Muralha Verde - GMV.bitstream/item/123193/1/DOC-174-Atelier-Orixas.pd